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/* Copyright (C) 2010-2013 B.A.T.M.A.N. contributors:
 *
 * Marek Lindner
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of version 2 of the GNU General Public
 * License as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301, USA
 */

#include "main.h"
#include "sysfs.h"
#include "translation-table.h"
#include "distributed-arp-table.h"
#include "originator.h"
#include "hard-interface.h"
#include "gateway_common.h"
#include "gateway_client.h"
#include "vis.h"

static struct net_device *batadv_kobj_to_netdev(struct kobject *obj)
{
	struct device *dev = container_of(obj->parent, struct device, kobj);
	return to_net_dev(dev);
}

static struct batadv_priv *batadv_kobj_to_batpriv(struct kobject *obj)
{
	struct net_device *net_dev = batadv_kobj_to_netdev(obj);
	return netdev_priv(net_dev);
}

#define BATADV_UEV_TYPE_VAR	"BATTYPE="
#define BATADV_UEV_ACTION_VAR	"BATACTION="
#define BATADV_UEV_DATA_VAR	"BATDATA="

static char *batadv_uev_action_str[] = {
	"add",
	"del",
	"change"
};

static char *batadv_uev_type_str[] = {
	"gw"
};

/* Use this, if you have customized show and store functions */
#define BATADV_ATTR(_name, _mode, _show, _store)	\
struct batadv_attribute batadv_attr_##_name = {		\
	.attr = {.name = __stringify(_name),		\
		 .mode = _mode },			\
	.show   = _show,				\
	.store  = _store,				\
};

#define BATADV_ATTR_SIF_STORE_BOOL(_name, _post_func)			\
ssize_t batadv_store_##_name(struct kobject *kobj,			\
			     struct attribute *attr, char *buff,	\
			     size_t count)				\
{									\
	struct net_device *net_dev = batadv_kobj_to_netdev(kobj);	\
	struct batadv_priv *bat_priv = netdev_priv(net_dev);		\
	return __batadv_store_bool_attr(buff, count, _post_func, attr,	\
					&bat_priv->_name, net_dev);	\
}

#define BATADV_ATTR_SIF_SHOW_BOOL(_name)				\
ssize_t batadv_show_##_name(struct kobject *kobj,			\
			    struct attribute *attr, char *buff)		\
{									\
	struct batadv_priv *bat_priv = batadv_kobj_to_batpriv(kobj);	\
	return sprintf(buff, "%s\n",					\
		       atomic_read(&bat_priv->_name) == 0 ?		\
		       "disabled" : "enabled");				\
}									\

/* Use this, if you are going to turn a [name] in the soft-interface
 * (bat_priv) on or off
 */
#define BATADV_ATTR_SIF_BOOL(_name, _mode, _post_func)			\
	static BATADV_ATTR_SIF_STORE_BOOL(_name, _post_func)		\
	static BATADV_ATTR_SIF_SHOW_BOOL(_name)				\
	static BATADV_ATTR(_name, _mode, batadv_show_##_name,		\
			   batadv_store_##_name)


#define BATADV_ATTR_SIF_STORE_UINT(_name, _min, _max, _post_func)	\
ssize_t batadv_store_##_name(struct kobject *kobj,			\
			     struct attribute *attr, char *buff,	\
			     size_t count)				\
{									\
	struct net_device *net_dev = batadv_kobj_to_netdev(kobj);	\
	struct batadv_priv *bat_priv = netdev_priv(net_dev);		\
	return __batadv_store_uint_attr(buff, count, _min, _max,	\
					_post_func, attr,		\
					&bat_priv->_name, net_dev);	\
}

#define BATADV_ATTR_SIF_SHOW_UINT(_name)				\
ssize_t batadv_show_##_name(struct kobject *kobj,			\
			    struct attribute *attr, char *buff)		\
{									\
	struct batadv_priv *bat_priv = batadv_kobj_to_batpriv(kobj);	\
	return sprintf(buff, "%i\n", atomic_read(&bat_priv->_name));	\
}									\

/* Use this, if you are going to set [name] in the soft-interface
 * (bat_priv) to an unsigned integer value
 */
#define BATADV_ATTR_SIF_UINT(_name, _mode, _min, _max, _post_func)	\
	static BATADV_ATTR_SIF_STORE_UINT(_name, _min, _max, _post_func)\
	static BATADV_ATTR_SIF_SHOW_UINT(_name)				\
	static BATADV_ATTR(_name, _mode, batadv_show_##_name,		\
			   batadv_store_##_name)


static int batadv_store_bool_attr(char *buff, size_t count,
				  struct net_device *net_dev,
				  const char *attr_name, atomic_t *attr)
{
	int enabled = -1;

	if (buff[count - 1] == '\n')
		buff[count - 1] = '\0';

	if ((strncmp(buff, "1", 2) == 0) ||
	    (strncmp(buff, "enable", 7) == 0) ||
	    (strncmp(buff, "enabled", 8) == 0))
		enabled = 1;

	if ((strncmp(buff, "0", 2) == 0) ||
	    (strncmp(buff, "disable", 8) == 0) ||
	    (strncmp(buff, "disabled", 9) == 0))
		enabled = 0;

	if (enabled < 0) {
		batadv_info(net_dev, "%s: Invalid parameter received: %s\n",
			    attr_name, buff);
		return -EINVAL;
	}

	if (atomic_read(attr) == enabled)
		return count;

	batadv_info(net_dev, "%s: Changing from: %s to: %s\n", attr_name,
		    atomic_read(attr) == 1 ? "enabled" : "disabled",
		    enabled == 1 ? "enabled" : "disabled");

	atomic_set(attr, (unsigned int)enabled);
	return count;
}

static inline ssize_t
__batadv_store_bool_attr(char *buff, size_t count,
			 void (*post_func)(struct net_device *),
			 struct attribute *attr,
			 atomic_t *attr_store, struct net_device *net_dev)
{
	int ret;

	ret = batadv_store_bool_attr(buff, count, net_dev, attr->name,
				     attr_store);
	if (post_func && ret)
		post_func(net_dev);

	return ret;
}

static int batadv_store_uint_attr(const char *buff, size_t count,
				  struct net_device *net_dev,
				  const char *attr_name,
				  unsigned int min, unsigned int max,
				  atomic_t *attr)
{
	unsigned long uint_val;
	int ret;

	ret = kstrtoul(buff, 10, &uint_val);
	if (ret) {
		batadv_info(net_dev, "%s: Invalid parameter received: %s\n",
			    attr_name, buff);
		return -EINVAL;
	}

	if (uint_val < min) {
		batadv_info(net_dev, "%s: Value is too small: %lu min: %u\n",
			    attr_name, uint_val, min);
		return -EINVAL;
	}

	if (uint_val > max) {
		batadv_info(net_dev, "%s: Value is too big: %lu max: %u\n",
			    attr_name, uint_val, max);
		return -EINVAL;
	}

	if (atomic_read(attr) == uint_val)
		return count;

	batadv_info(net_dev, "%s: Changing from: %i to: %lu\n",
		    attr_name, atomic_read(attr), uint_val);

	atomic_set(attr, uint_val);
	return count;
}

static inline ssize_t
__batadv_store_uint_attr(const char *buff, size_t count,
			 int min, int max,
			 void (*post_func)(struct net_device *),
			 const struct attribute *attr,
			 atomic_t *attr_store, struct net_device *net_dev)
{
	int ret;

	ret = batadv_store_uint_attr(buff, count, net_dev, attr->name, min, max,
				     attr_store);
	if (post_func && ret)
		post_func(net_dev);

	return ret;
}

static ssize_t batadv_show_vis_mode(struct kobject *kobj,
				    struct attribute *attr, char *buff)
{
	struct batadv_priv *bat_priv = batadv_kobj_to_batpriv(kobj);
	int vis_mode = atomic_read(&bat_priv->vis_mode);
	const char *mode;

	if (vis_mode == BATADV_VIS_TYPE_CLIENT_UPDATE)
		mode = "client";
	else
		mode = "server";

	return sprintf(buff, "%s\n", mode);
}

static ssize_t batadv_store_vis_mode(struct kobject *kobj,
				     struct attribute *attr, char *buff,
				     size_t count)
{
	struct net_device *net_dev = batadv_kobj_to_netdev(kobj);
	struct batadv_priv *bat_priv = netdev_priv(net_dev);
	unsigned long val;
	int ret, vis_mode_tmp = -1;
	const char *old_mode, *new_mode;

	ret = kstrtoul(buff, 10, &val);

	if (((count == 2) && (!ret) &&
	     (val == BATADV_VIS_TYPE_CLIENT_UPDATE)) ||
	    (strncmp(buff, "client", 6) == 0) ||
	    (strncmp(buff, "off", 3) == 0))
		vis_mode_tmp = BATADV_VIS_TYPE_CLIENT_UPDATE;

	if (((count == 2) && (!ret) &&
	     (val == BATADV_VIS_TYPE_SERVER_SYNC)) ||
	    (strncmp(buff, "server", 6) == 0))
		vis_mode_tmp = BATADV_VIS_TYPE_SERVER_SYNC;

	if (vis_mode_tmp < 0) {
		if (buff[count - 1] == '\n')
			buff[count - 1] = '\0';

		batadv_info(net_dev,
			    "Invalid parameter for 'vis mode' setting received: %s\n",
			    buff);
		return -EINVAL;
	}

	if (atomic_read(&bat_priv->vis_mode) == vis_mode_tmp)
		return count;

	if (atomic_read(&bat_priv->vis_mode) == BATADV_VIS_TYPE_CLIENT_UPDATE)
		old_mode =  "client";
	else
		old_mode = "server";

	if (vis_mode_tmp == BATADV_VIS_TYPE_CLIENT_UPDATE)
		new_mode =  "client";
	else
		new_mode = "server";

	batadv_info(net_dev, "Changing vis mode from: %s to: %s\n", old_mode,
		    new_mode);

	atomic_set(&bat_priv->vis_mode, (unsigned int)vis_mode_tmp);
	return count;
}

static ssize_t batadv_show_bat_algo(struct kobject *kobj,
				    struct attribute *attr, char *buff)
{
	struct batadv_priv *bat_priv = batadv_kobj_to_batpriv(kobj);
	return sprintf(buff, "%s\n", bat_priv->bat_algo_ops->name);
}

static void batadv_post_gw_deselect(struct net_device *net_dev)
{
	struct batadv_priv *bat_priv = netdev_priv(net_dev);
	batadv_gw_deselect(bat_priv);
}

static ssize_t batadv_show_gw_mode(struct kobject *kobj, struct attribute *attr,
				   char *buff)
{
	struct batadv_priv *bat_priv = batadv_kobj_to_batpriv(kobj);
	int bytes_written;

	switch (atomic_read(&bat_priv->gw_mode)) {
	case BATADV_GW_MODE_CLIENT:
		bytes_written = sprintf(buff, "%s\n",
					BATADV_GW_MODE_CLIENT_NAME);
		break;
	case BATADV_GW_MODE_SERVER:
		bytes_written = sprintf(buff, "%s\n",
					BATADV_GW_MODE_SERVER_NAME);
		break;
	default:
		bytes_written = sprintf(buff, "%s\n",
					BATADV_GW_MODE_OFF_NAME);
		break;
	}

	return bytes_written;
}

static ssize_t batadv_store_gw_mode(struct kobject *kobj,
				    struct attribute *attr, char *buff,
				    size_t count)
{
	struct net_device *net_dev = batadv_kobj_to_netdev(kobj);
	struct batadv_priv *bat_priv = netdev_priv(net_dev);
	char *curr_gw_mode_str;
	int gw_mode_tmp = -1;

	if (buff[count - 1] == '\n')
		buff[count - 1] = '\0';

	if (strncmp(buff, BATADV_GW_MODE_OFF_NAME,
		    strlen(BATADV_GW_MODE_OFF_NAME)) == 0)
		gw_mode_tmp = BATADV_GW_MODE_OFF;

	if (strncmp(buff, BATADV_GW_MODE_CLIENT_NAME,
		    strlen(BATADV_GW_MODE_CLIENT_NAME)) == 0)
		gw_mode_tmp = BATADV_GW_MODE_CLIENT;

	if (strncmp(buff, BATADV_GW_MODE_SERVER_NAME,
		    strlen(BATADV_GW_MODE_SERVER_NAME)) == 0)
		gw_mode_tmp = BATADV_GW_MODE_SERVER;

	if (gw_mode_tmp < 0) {
		batadv_info(net_dev,
			    "Invalid parameter for 'gw mode' setting received: %s\n",
			    buff);
		return -EINVAL;
	}

	if (atomic_read(&bat_priv->gw_mode) == gw_mode_tmp)
		return count;

	switch (atomic_read(&bat_priv->gw_mode)) {
	case BATADV_GW_MODE_CLIENT:
		curr_gw_mode_str = BATADV_GW_MODE_CLIENT_NAME;
		break;
	case BATADV_GW_MODE_SERVER:
		curr_gw_mode_str = BATADV_GW_MODE_SERVER_NAME;
		break;
	default:
		curr_gw_mode_str = BATADV_GW_MODE_OFF_NAME;
		break;
	}

	batadv_info(net_dev, "Changing gw mode from: %s to: %s\n",
		    curr_gw_mode_str, buff);

	batadv_gw_deselect(bat_priv);
	atomic_set(&bat_priv->gw_mode, (unsigned int)gw_mode_tmp);
	return count;
}

static ssize_t batadv_show_gw_bwidth(struct kobject *kobj,
				     struct attribute *attr, char *buff)
{
	struct batadv_priv *bat_priv = batadv_kobj_to_batpriv(kobj);
	int down, up;
	int gw_bandwidth = atomic_read(&bat_priv->gw_bandwidth);

	batadv_gw_bandwidth_to_kbit(gw_bandwidth, &down, &up);
	return sprintf(buff, "%i%s/%i%s\n",
		       (down > 2048 ? down / 1024 : down),
		       (down > 2048 ? "MBit" : "KBit"),
		       (up > 2048 ? up / 1024 : up),
		       (up > 2048 ? "MBit" : "KBit"));
}

static ssize_t batadv_store_gw_bwidth(struct kobject *kobj,
				      struct attribute *attr, char *buff,
				      size_t count)
{
	struct net_device *net_dev = batadv_kobj_to_netdev(kobj);

	if (buff[count - 1] == '\n')
		buff[count - 1] = '\0';

	return batadv_gw_bandwidth_set(net_dev, buff, count);
}

BATADV_ATTR_SIF_BOOL(aggregated_ogms, S_IRUGO | S_IWUSR, NULL);
BATADV_ATTR_SIF_BOOL(bonding, S_IRUGO | S_IWUSR, NULL);
#ifdef CONFIG_BATMAN_ADV_BLA
BATADV_ATTR_SIF_BOOL(bridge_loop_avoidance, S_IRUGO | S_IWUSR, NULL);
#endif
#ifdef CONFIG_BATMAN_ADV_DAT
BATADV_ATTR_SIF_BOOL(distributed_arp_table, S_IRUGO | S_IWUSR, NULL);
#endif
BATADV_ATTR_SIF_BOOL(fragmentation, S_IRUGO | S_IWUSR, batadv_update_min_mtu);
BATADV_ATTR_SIF_BOOL(ap_isolation, S_IRUGO | S_IWUSR, NULL);
static BATADV_ATTR(vis_mode, S_IRUGO | S_IWUSR, batadv_show_vis_mode,
		   batadv_store_vis_mode);
static BATADV_ATTR(routing_algo, S_IRUGO, batadv_show_bat_algo, NULL);
static BATADV_ATTR(gw_mode, S_IRUGO | S_IWUSR, batadv_show_gw_mode,
		   batadv_store_gw_mode);
BATADV_ATTR_SIF_UINT(orig_interval, S_IRUGO | S_IWUSR, 2 * BATADV_JITTER,
		     INT_MAX, NULL);
BATADV_ATTR_SIF_UINT(hop_penalty, S_IRUGO | S_IWUSR, 0, BATADV_TQ_MAX_VALUE,
		     NULL);
BATADV_ATTR_SIF_UINT(gw_sel_class, S_IRUGO | S_IWUSR, 1, BATADV_TQ_MAX_VALUE,
		     batadv_post_gw_deselect);
static BATADV_ATTR(gw_bandwidth, S_IRUGO | S_IWUSR, batadv_show_gw_bwidth,
		   batadv_store_gw_bwidth);
#ifdef CONFIG_BATMAN_ADV_DEBUG
BATADV_ATTR_SIF_UINT(log_level, S_IRUGO | S_IWUSR, 0, BATADV_DBG_ALL, NULL);
#endif

static struct batadv_attribute *batadv_mesh_attrs[] = {
	&batadv_attr_aggregated_ogms,
	&batadv_attr_bonding,
#ifdef CONFIG_BATMAN_ADV_BLA
	&batadv_attr_bridge_loop_avoidance,
#endif
#ifdef CONFIG_BATMAN_ADV_DAT
	&batadv_attr_distributed_arp_table,
#endif
	&batadv_attr_fragmentation,
	&batadv_attr_ap_isolation,
	&batadv_attr_vis_mode,
	&batadv_attr_routing_algo,
	&batadv_attr_gw_mode,
	&batadv_attr_orig_interval,
	&batadv_attr_hop_penalty,
	&batadv_attr_gw_sel_class,
	&batadv_attr_gw_bandwidth,
#ifdef CONFIG_BATMAN_ADV_DEBUG
	&batadv_attr_log_level,
#endif
	NULL,
};

int batadv_sysfs_add_meshif(struct net_device *dev)
{
	struct kobject *batif_kobject = &dev->dev.kobj;
	struct batadv_priv *bat_priv = netdev_priv(dev);
	struct batadv_attribute **bat_attr;
	int err;

	bat_priv->mesh_obj = kobject_create_and_add(BATADV_SYSFS_IF_MESH_SUBDIR,
						    batif_kobject);
	if (!bat_priv->mesh_obj) {
		batadv_err(dev, "Can't add sysfs directory: %s/%s\n", dev->name,
			   BATADV_SYSFS_IF_MESH_SUBDIR);
		goto out;
	}

	for (bat_attr = batadv_mesh_attrs; *bat_attr; ++bat_attr) {
		err = sysfs_create_file(bat_priv->mesh_obj,
					&((*bat_attr)->attr));
		if (err) {
			batadv_err(dev, "Can't add sysfs file: %s/%s/%s\n",
				   dev->name, BATADV_SYSFS_IF_MESH_SUBDIR,
				   ((*bat_attr)->attr).name);
			goto rem_attr;
		}
	}

	return 0;

rem_attr:
	for (bat_attr = batadv_mesh_attrs; *bat_attr; ++bat_attr)
		sysfs_remove_file(bat_priv->mesh_obj, &((*bat_attr)->attr));

	kobject_put(bat_priv->mesh_obj);
	bat_priv->mesh_obj = NULL;
out:
	return -ENOMEM;
}

void batadv_sysfs_del_meshif(struct net_device *dev)
{
	struct batadv_priv *bat_priv = netdev_priv(dev);
	struct batadv_attribute **bat_attr;

	for (bat_attr = batadv_mesh_attrs; *bat_attr; ++bat_attr)
		sysfs_remove_file(bat_priv->mesh_obj, &((*bat_attr)->attr));

	kobject_put(bat_priv->mesh_obj);
	bat_priv->mesh_obj = NULL;
}

static ssize_t batadv_show_mesh_iface(struct kobject *kobj,
				      struct attribute *attr, char *buff)
{
	struct net_device *net_dev = batadv_kobj_to_netdev(kobj);
	struct batadv_hard_iface *hard_iface;
	ssize_t length;
	const char *ifname;

	hard_iface = batadv_hardif_get_by_netdev(net_dev);
	if (!hard_iface)
		return 0;

	if (hard_iface->if_status == BATADV_IF_NOT_IN_USE)
		ifname =  "none";
	else
		ifname = hard_iface->soft_iface->name;

	length = sprintf(buff, "%s\n", ifname);

	batadv_hardif_free_ref(hard_iface);

	return length;
}

static ssize_t batadv_store_mesh_iface(struct kobject *kobj,
				       struct attribute *attr, char *buff,
				       size_t count)
{
	struct net_device *net_dev = batadv_kobj_to_netdev(kobj);
	struct batadv_hard_iface *hard_iface;
	int status_tmp = -1;
	int ret = count;

	hard_iface = batadv_hardif_get_by_netdev(net_dev);
	if (!hard_iface)
		return count;

	if (buff[count - 1] == '\n')
		buff[count - 1] = '\0';

	if (strlen(buff) >= IFNAMSIZ) {
		pr_err("Invalid parameter for 'mesh_iface' setting received: interface name too long '%s'\n",
		       buff);
		batadv_hardif_free_ref(hard_iface);
		return -EINVAL;
	}

	if (strncmp(buff, "none", 4) == 0)
		status_tmp = BATADV_IF_NOT_IN_USE;
	else
		status_tmp = BATADV_IF_I_WANT_YOU;

	if (hard_iface->if_status == status_tmp)
		goto out;

	if ((hard_iface->soft_iface) &&
	    (strncmp(hard_iface->soft_iface->name, buff, IFNAMSIZ) == 0))
		goto out;

	if (!rtnl_trylock()) {
		ret = -ERESTARTSYS;
		goto out;
	}

	if (status_tmp == BATADV_IF_NOT_IN_USE) {
		batadv_hardif_disable_interface(hard_iface);
		goto unlock;
	}

	/* if the interface already is in use */
	if (hard_iface->if_status != BATADV_IF_NOT_IN_USE)
		batadv_hardif_disable_interface(hard_iface);

	ret = batadv_hardif_enable_interface(hard_iface, buff);

unlock:
	rtnl_unlock();
out:
	batadv_hardif_free_ref(hard_iface);
	return ret;
}

static ssize_t batadv_show_iface_status(struct kobject *kobj,
					struct attribute *attr, char *buff)
{
	struct net_device *net_dev = batadv_kobj_to_netdev(kobj);
	struct batadv_hard_iface *hard_iface;
	ssize_t length;

	hard_iface = batadv_hardif_get_by_netdev(net_dev);
	if (!hard_iface)
		return 0;

	switch (hard_iface->if_status) {
	case BATADV_IF_TO_BE_REMOVED:
		length = sprintf(buff, "disabling\n");
		break;
	case BATADV_IF_INACTIVE:
		length = sprintf(buff, "inactive\n");
		break;
	case BATADV_IF_ACTIVE:
		length = sprintf(buff, "active\n");
		break;
	case BATADV_IF_TO_BE_ACTIVATED:
		length = sprintf(buff, "enabling\n");
		break;
	case BATADV_IF_NOT_IN_USE:
	default:
		length = sprintf(buff, "not in use\n");
		break;
	}

	batadv_hardif_free_ref(hard_iface);

	return length;
}

static BATADV_ATTR(mesh_iface, S_IRUGO | S_IWUSR, batadv_show_mesh_iface,
		   batadv_store_mesh_iface);
static BATADV_ATTR(iface_status, S_IRUGO, batadv_show_iface_status, NULL);

static struct batadv_attribute *batadv_batman_attrs[] = {
	&batadv_attr_mesh_iface,
	&batadv_attr_iface_status,
	NULL,
};

int batadv_sysfs_add_hardif(struct kobject **hardif_obj, struct net_device *dev)
{
	struct kobject *hardif_kobject = &dev->dev.kobj;
	struct batadv_attribute **bat_attr;
	int err;

	*hardif_obj = kobject_create_and_add(BATADV_SYSFS_IF_BAT_SUBDIR,
					     hardif_kobject);

	if (!*hardif_obj) {
		batadv_err(dev, "Can't add sysfs directory: %s/%s\n", dev->name,
			   BATADV_SYSFS_IF_BAT_SUBDIR);
		goto out;
	}

	for (bat_attr = batadv_batman_attrs; *bat_attr; ++bat_attr) {
		err = sysfs_create_file(*hardif_obj, &((*bat_attr)->attr));
		if (err) {
			batadv_err(dev, "Can't add sysfs file: %s/%s/%s\n",
				   dev->name, BATADV_SYSFS_IF_BAT_SUBDIR,
				   ((*bat_attr)->attr).name);
			goto rem_attr;
		}
	}

	return 0;

rem_attr:
	for (bat_attr = batadv_batman_attrs; *bat_attr; ++bat_attr)
		sysfs_remove_file(*hardif_obj, &((*bat_attr)->attr));
out:
	return -ENOMEM;
}

void batadv_sysfs_del_hardif(struct kobject **hardif_obj)
{
	kobject_put(*hardif_obj);
	*hardif_obj = NULL;
}

int batadv_throw_uevent(struct batadv_priv *bat_priv, enum batadv_uev_type type,
			enum batadv_uev_action action, const char *data)
{
	int ret = -ENOMEM;
	struct batadv_hard_iface *primary_if;
	struct kobject *bat_kobj;
	char *uevent_env[4] = { NULL, NULL, NULL, NULL };

	primary_if = batadv_primary_if_get_selected(bat_priv);
	if (!primary_if)
		goto out;

	bat_kobj = &primary_if->soft_iface->dev.kobj;

	uevent_env[0] = kmalloc(strlen(BATADV_UEV_TYPE_VAR) +
				strlen(batadv_uev_type_str[type]) + 1,
				GFP_ATOMIC);
	if (!uevent_env[0])
		goto out;

	sprintf(uevent_env[0], "%s%s", BATADV_UEV_TYPE_VAR,
		batadv_uev_type_str[type]);

	uevent_env[1] = kmalloc(strlen(BATADV_UEV_ACTION_VAR) +
				strlen(batadv_uev_action_str[action]) + 1,
				GFP_ATOMIC);
	if (!uevent_env[1])
		goto out;

	sprintf(uevent_env[1], "%s%s", BATADV_UEV_ACTION_VAR,
		batadv_uev_action_str[action]);

	/* If the event is DEL, ignore the data field */
	if (action != BATADV_UEV_DEL) {
		uevent_env[2] = kmalloc(strlen(BATADV_UEV_DATA_VAR) +
					strlen(data) + 1, GFP_ATOMIC);
		if (!uevent_env[2])
			goto out;

		sprintf(uevent_env[2], "%s%s", BATADV_UEV_DATA_VAR, data);
	}

	ret = kobject_uevent_env(bat_kobj, KOBJ_CHANGE, uevent_env);
out:
	kfree(uevent_env[0]);
	kfree(uevent_env[1]);
	kfree(uevent_env[2]);

	if (primary_if)
		batadv_hardif_free_ref(primary_if);

	if (ret)
		batadv_dbg(BATADV_DBG_BATMAN, bat_priv,
			   "Impossible to send uevent for (%s,%s,%s) event (err: %d)\n",
			   batadv_uev_type_str[type],
			   batadv_uev_action_str[action],
			   (action == BATADV_UEV_DEL ? "NULL" : data), ret);
	return ret;
}
60' href='#n3060'>3060 3061 3062 3063 3064 3065 3066 3067 3068 3069 3070 3071 3072 3073 3074 3075 3076 3077 3078 3079 3080 3081 3082 3083 3084 3085 3086 3087 3088 3089 3090 3091 3092 3093 3094 3095 3096 3097 3098 3099 3100 3101 3102 3103 3104 3105 3106 3107 3108 3109 3110 3111 3112 3113 3114 3115 3116 3117 3118 3119 3120 3121 3122 3123 3124 3125 3126 3127 3128 3129 3130 3131 3132 3133 3134 3135 3136 3137 3138 3139 3140 3141 3142 3143 3144 3145 3146 3147 3148 3149 3150 3151 3152 3153 3154 3155 3156 3157 3158 3159 3160 3161 3162 3163 3164 3165 3166 3167 3168 3169 3170 3171 3172 3173 3174 3175 3176 3177 3178 3179 3180 3181 3182 3183 3184 3185 3186 3187 3188 3189 3190 3191 3192 3193 3194 3195 3196 3197 3198 3199 3200 3201 3202 3203 3204 3205 3206 3207 3208 3209 3210 3211 3212 3213 3214 3215 3216 3217 3218 3219 3220 3221 3222 3223 3224 3225 3226 3227 3228 3229 3230 3231 3232 3233 3234 3235 3236 3237 3238 3239 3240 3241 3242 3243 3244 3245 3246 3247 3248 3249 3250 3251 3252 3253 3254 3255 3256 3257 3258 3259 3260 3261 3262 3263 3264 3265 3266 3267 3268 3269 3270 3271 3272 3273 3274 3275 3276 3277 3278 3279 3280 3281 3282 3283 3284 3285 3286 3287 3288 3289 3290 3291 3292 3293 3294 3295 3296 3297 3298 3299 3300 3301 3302 3303 3304 3305 3306 3307 3308 3309 3310 3311 3312 3313 3314 3315 3316 3317 3318 3319 3320 3321 3322 3323 3324 3325 3326 3327 3328 3329 3330 3331 3332 3333 3334 3335 3336 3337 3338 3339 3340 3341 3342 3343 3344 3345 3346 3347 3348 3349 3350 3351 3352 3353
/*
 * INET		An implementation of the TCP/IP protocol suite for the LINUX
 *		operating system.  INET is implemented using the  BSD Socket
 *		interface as the means of communication with the user level.
 *
 *		Implementation of the Transmission Control Protocol(TCP).
 *
 * Authors:	Ross Biro
 *		Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
 *		Mark Evans, <evansmp@uhura.aston.ac.uk>
 *		Corey Minyard <wf-rch!minyard@relay.EU.net>
 *		Florian La Roche, <flla@stud.uni-sb.de>
 *		Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
 *		Linus Torvalds, <torvalds@cs.helsinki.fi>
 *		Alan Cox, <gw4pts@gw4pts.ampr.org>
 *		Matthew Dillon, <dillon@apollo.west.oic.com>
 *		Arnt Gulbrandsen, <agulbra@nvg.unit.no>
 *		Jorge Cwik, <jorge@laser.satlink.net>
 */

/*
 * Changes:	Pedro Roque	:	Retransmit queue handled by TCP.
 *				:	Fragmentation on mtu decrease
 *				:	Segment collapse on retransmit
 *				:	AF independence
 *
 *		Linus Torvalds	:	send_delayed_ack
 *		David S. Miller	:	Charge memory using the right skb
 *					during syn/ack processing.
 *		David S. Miller :	Output engine completely rewritten.
 *		Andrea Arcangeli:	SYNACK carry ts_recent in tsecr.
 *		Cacophonix Gaul :	draft-minshall-nagle-01
 *		J Hadi Salim	:	ECN support
 *
 */

#define pr_fmt(fmt) "TCP: " fmt

#include <net/tcp.h>

#include <linux/compiler.h>
#include <linux/gfp.h>
#include <linux/module.h>

/* People can turn this off for buggy TCP's found in printers etc. */
int sysctl_tcp_retrans_collapse __read_mostly = 1;

/* People can turn this on to work with those rare, broken TCPs that
 * interpret the window field as a signed quantity.
 */
int sysctl_tcp_workaround_signed_windows __read_mostly = 0;

/* Default TSQ limit of two TSO segments */
int sysctl_tcp_limit_output_bytes __read_mostly = 131072;

/* This limits the percentage of the congestion window which we
 * will allow a single TSO frame to consume.  Building TSO frames
 * which are too large can cause TCP streams to be bursty.
 */
int sysctl_tcp_tso_win_divisor __read_mostly = 3;

int sysctl_tcp_mtu_probing __read_mostly = 0;
int sysctl_tcp_base_mss __read_mostly = TCP_BASE_MSS;

/* By default, RFC2861 behavior.  */
int sysctl_tcp_slow_start_after_idle __read_mostly = 1;

unsigned int sysctl_tcp_notsent_lowat __read_mostly = UINT_MAX;
EXPORT_SYMBOL(sysctl_tcp_notsent_lowat);

static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
			   int push_one, gfp_t gfp);

/* Account for new data that has been sent to the network. */
static void tcp_event_new_data_sent(struct sock *sk, const struct sk_buff *skb)
{
	struct inet_connection_sock *icsk = inet_csk(sk);
	struct tcp_sock *tp = tcp_sk(sk);
	unsigned int prior_packets = tp->packets_out;

	tcp_advance_send_head(sk, skb);
	tp->snd_nxt = TCP_SKB_CB(skb)->end_seq;

	tp->packets_out += tcp_skb_pcount(skb);
	if (!prior_packets || icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS ||
	    icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) {
		tcp_rearm_rto(sk);
	}

	NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPORIGDATASENT,
		      tcp_skb_pcount(skb));
}

/* SND.NXT, if window was not shrunk.
 * If window has been shrunk, what should we make? It is not clear at all.
 * Using SND.UNA we will fail to open window, SND.NXT is out of window. :-(
 * Anything in between SND.UNA...SND.UNA+SND.WND also can be already
 * invalid. OK, let's make this for now:
 */
static inline __u32 tcp_acceptable_seq(const struct sock *sk)
{
	const struct tcp_sock *tp = tcp_sk(sk);

	if (!before(tcp_wnd_end(tp), tp->snd_nxt))
		return tp->snd_nxt;
	else
		return tcp_wnd_end(tp);
}

/* Calculate mss to advertise in SYN segment.
 * RFC1122, RFC1063, draft-ietf-tcpimpl-pmtud-01 state that:
 *
 * 1. It is independent of path mtu.
 * 2. Ideally, it is maximal possible segment size i.e. 65535-40.
 * 3. For IPv4 it is reasonable to calculate it from maximal MTU of
 *    attached devices, because some buggy hosts are confused by
 *    large MSS.
 * 4. We do not make 3, we advertise MSS, calculated from first
 *    hop device mtu, but allow to raise it to ip_rt_min_advmss.
 *    This may be overridden via information stored in routing table.
 * 5. Value 65535 for MSS is valid in IPv6 and means "as large as possible,
 *    probably even Jumbo".
 */
static __u16 tcp_advertise_mss(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);
	const struct dst_entry *dst = __sk_dst_get(sk);
	int mss = tp->advmss;

	if (dst) {
		unsigned int metric = dst_metric_advmss(dst);

		if (metric < mss) {
			mss = metric;
			tp->advmss = mss;
		}
	}

	return (__u16)mss;
}

/* RFC2861. Reset CWND after idle period longer RTO to "restart window".
 * This is the first part of cwnd validation mechanism. */
static void tcp_cwnd_restart(struct sock *sk, const struct dst_entry *dst)
{
	struct tcp_sock *tp = tcp_sk(sk);
	s32 delta = tcp_time_stamp - tp->lsndtime;
	u32 restart_cwnd = tcp_init_cwnd(tp, dst);
	u32 cwnd = tp->snd_cwnd;

	tcp_ca_event(sk, CA_EVENT_CWND_RESTART);

	tp->snd_ssthresh = tcp_current_ssthresh(sk);
	restart_cwnd = min(restart_cwnd, cwnd);

	while ((delta -= inet_csk(sk)->icsk_rto) > 0 && cwnd > restart_cwnd)
		cwnd >>= 1;
	tp->snd_cwnd = max(cwnd, restart_cwnd);
	tp->snd_cwnd_stamp = tcp_time_stamp;
	tp->snd_cwnd_used = 0;
}

/* Congestion state accounting after a packet has been sent. */
static void tcp_event_data_sent(struct tcp_sock *tp,
				struct sock *sk)
{
	struct inet_connection_sock *icsk = inet_csk(sk);
	const u32 now = tcp_time_stamp;
	const struct dst_entry *dst = __sk_dst_get(sk);

	if (sysctl_tcp_slow_start_after_idle &&
	    (!tp->packets_out && (s32)(now - tp->lsndtime) > icsk->icsk_rto))
		tcp_cwnd_restart(sk, __sk_dst_get(sk));

	tp->lsndtime = now;

	/* If it is a reply for ato after last received
	 * packet, enter pingpong mode.
	 */
	if ((u32)(now - icsk->icsk_ack.lrcvtime) < icsk->icsk_ack.ato &&
	    (!dst || !dst_metric(dst, RTAX_QUICKACK)))
			icsk->icsk_ack.pingpong = 1;
}

/* Account for an ACK we sent. */
static inline void tcp_event_ack_sent(struct sock *sk, unsigned int pkts)
{
	tcp_dec_quickack_mode(sk, pkts);
	inet_csk_clear_xmit_timer(sk, ICSK_TIME_DACK);
}


u32 tcp_default_init_rwnd(u32 mss)
{
	/* Initial receive window should be twice of TCP_INIT_CWND to
	 * enable proper sending of new unsent data during fast recovery
	 * (RFC 3517, Section 4, NextSeg() rule (2)). Further place a
	 * limit when mss is larger than 1460.
	 */
	u32 init_rwnd = TCP_INIT_CWND * 2;

	if (mss > 1460)
		init_rwnd = max((1460 * init_rwnd) / mss, 2U);
	return init_rwnd;
}

/* Determine a window scaling and initial window to offer.
 * Based on the assumption that the given amount of space
 * will be offered. Store the results in the tp structure.
 * NOTE: for smooth operation initial space offering should
 * be a multiple of mss if possible. We assume here that mss >= 1.
 * This MUST be enforced by all callers.
 */
void tcp_select_initial_window(int __space, __u32 mss,
			       __u32 *rcv_wnd, __u32 *window_clamp,
			       int wscale_ok, __u8 *rcv_wscale,
			       __u32 init_rcv_wnd)
{
	unsigned int space = (__space < 0 ? 0 : __space);

	/* If no clamp set the clamp to the max possible scaled window */
	if (*window_clamp == 0)
		(*window_clamp) = (65535 << 14);
	space = min(*window_clamp, space);

	/* Quantize space offering to a multiple of mss if possible. */
	if (space > mss)
		space = (space / mss) * mss;

	/* NOTE: offering an initial window larger than 32767
	 * will break some buggy TCP stacks. If the admin tells us
	 * it is likely we could be speaking with such a buggy stack
	 * we will truncate our initial window offering to 32K-1
	 * unless the remote has sent us a window scaling option,
	 * which we interpret as a sign the remote TCP is not
	 * misinterpreting the window field as a signed quantity.
	 */
	if (sysctl_tcp_workaround_signed_windows)
		(*rcv_wnd) = min(space, MAX_TCP_WINDOW);
	else
		(*rcv_wnd) = space;

	(*rcv_wscale) = 0;
	if (wscale_ok) {
		/* Set window scaling on max possible window
		 * See RFC1323 for an explanation of the limit to 14
		 */
		space = max_t(u32, sysctl_tcp_rmem[2], sysctl_rmem_max);
		space = min_t(u32, space, *window_clamp);
		while (space > 65535 && (*rcv_wscale) < 14) {
			space >>= 1;
			(*rcv_wscale)++;
		}
	}

	if (mss > (1 << *rcv_wscale)) {
		if (!init_rcv_wnd) /* Use default unless specified otherwise */
			init_rcv_wnd = tcp_default_init_rwnd(mss);
		*rcv_wnd = min(*rcv_wnd, init_rcv_wnd * mss);
	}

	/* Set the clamp no higher than max representable value */
	(*window_clamp) = min(65535U << (*rcv_wscale), *window_clamp);
}
EXPORT_SYMBOL(tcp_select_initial_window);

/* Chose a new window to advertise, update state in tcp_sock for the
 * socket, and return result with RFC1323 scaling applied.  The return
 * value can be stuffed directly into th->window for an outgoing
 * frame.
 */
static u16 tcp_select_window(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);
	u32 old_win = tp->rcv_wnd;
	u32 cur_win = tcp_receive_window(tp);
	u32 new_win = __tcp_select_window(sk);

	/* Never shrink the offered window */
	if (new_win < cur_win) {
		/* Danger Will Robinson!
		 * Don't update rcv_wup/rcv_wnd here or else
		 * we will not be able to advertise a zero
		 * window in time.  --DaveM
		 *
		 * Relax Will Robinson.
		 */
		if (new_win == 0)
			NET_INC_STATS(sock_net(sk),
				      LINUX_MIB_TCPWANTZEROWINDOWADV);
		new_win = ALIGN(cur_win, 1 << tp->rx_opt.rcv_wscale);
	}
	tp->rcv_wnd = new_win;
	tp->rcv_wup = tp->rcv_nxt;

	/* Make sure we do not exceed the maximum possible
	 * scaled window.
	 */
	if (!tp->rx_opt.rcv_wscale && sysctl_tcp_workaround_signed_windows)
		new_win = min(new_win, MAX_TCP_WINDOW);
	else
		new_win = min(new_win, (65535U << tp->rx_opt.rcv_wscale));

	/* RFC1323 scaling applied */
	new_win >>= tp->rx_opt.rcv_wscale;

	/* If we advertise zero window, disable fast path. */
	if (new_win == 0) {
		tp->pred_flags = 0;
		if (old_win)
			NET_INC_STATS(sock_net(sk),
				      LINUX_MIB_TCPTOZEROWINDOWADV);
	} else if (old_win == 0) {
		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFROMZEROWINDOWADV);
	}

	return new_win;
}

/* Packet ECN state for a SYN-ACK */
static void tcp_ecn_send_synack(struct sock *sk, struct sk_buff *skb)
{
	const struct tcp_sock *tp = tcp_sk(sk);

	TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_CWR;
	if (!(tp->ecn_flags & TCP_ECN_OK))
		TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_ECE;
	else if (tcp_ca_needs_ecn(sk))
		INET_ECN_xmit(sk);
}

/* Packet ECN state for a SYN.  */
static void tcp_ecn_send_syn(struct sock *sk, struct sk_buff *skb)
{
	struct tcp_sock *tp = tcp_sk(sk);

	tp->ecn_flags = 0;
	if (sock_net(sk)->ipv4.sysctl_tcp_ecn == 1 ||
	    tcp_ca_needs_ecn(sk)) {
		TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ECE | TCPHDR_CWR;
		tp->ecn_flags = TCP_ECN_OK;
		if (tcp_ca_needs_ecn(sk))
			INET_ECN_xmit(sk);
	}
}

static void
tcp_ecn_make_synack(const struct request_sock *req, struct tcphdr *th,
		    struct sock *sk)
{
	if (inet_rsk(req)->ecn_ok) {
		th->ece = 1;
		if (tcp_ca_needs_ecn(sk))
			INET_ECN_xmit(sk);
	}
}

/* Set up ECN state for a packet on a ESTABLISHED socket that is about to
 * be sent.
 */
static void tcp_ecn_send(struct sock *sk, struct sk_buff *skb,
				int tcp_header_len)
{
	struct tcp_sock *tp = tcp_sk(sk);

	if (tp->ecn_flags & TCP_ECN_OK) {
		/* Not-retransmitted data segment: set ECT and inject CWR. */
		if (skb->len != tcp_header_len &&
		    !before(TCP_SKB_CB(skb)->seq, tp->snd_nxt)) {
			INET_ECN_xmit(sk);
			if (tp->ecn_flags & TCP_ECN_QUEUE_CWR) {
				tp->ecn_flags &= ~TCP_ECN_QUEUE_CWR;
				tcp_hdr(skb)->cwr = 1;
				skb_shinfo(skb)->gso_type |= SKB_GSO_TCP_ECN;
			}
		} else if (!tcp_ca_needs_ecn(sk)) {
			/* ACK or retransmitted segment: clear ECT|CE */
			INET_ECN_dontxmit(sk);
		}
		if (tp->ecn_flags & TCP_ECN_DEMAND_CWR)
			tcp_hdr(skb)->ece = 1;
	}
}

/* Constructs common control bits of non-data skb. If SYN/FIN is present,
 * auto increment end seqno.
 */
static void tcp_init_nondata_skb(struct sk_buff *skb, u32 seq, u8 flags)
{
	struct skb_shared_info *shinfo = skb_shinfo(skb);

	skb->ip_summed = CHECKSUM_PARTIAL;
	skb->csum = 0;

	TCP_SKB_CB(skb)->tcp_flags = flags;
	TCP_SKB_CB(skb)->sacked = 0;

	tcp_skb_pcount_set(skb, 1);
	shinfo->gso_size = 0;
	shinfo->gso_type = 0;

	TCP_SKB_CB(skb)->seq = seq;
	if (flags & (TCPHDR_SYN | TCPHDR_FIN))
		seq++;
	TCP_SKB_CB(skb)->end_seq = seq;
}

static inline bool tcp_urg_mode(const struct tcp_sock *tp)
{
	return tp->snd_una != tp->snd_up;
}

#define OPTION_SACK_ADVERTISE	(1 << 0)
#define OPTION_TS		(1 << 1)
#define OPTION_MD5		(1 << 2)
#define OPTION_WSCALE		(1 << 3)
#define OPTION_FAST_OPEN_COOKIE	(1 << 8)

struct tcp_out_options {
	u16 options;		/* bit field of OPTION_* */
	u16 mss;		/* 0 to disable */
	u8 ws;			/* window scale, 0 to disable */
	u8 num_sack_blocks;	/* number of SACK blocks to include */
	u8 hash_size;		/* bytes in hash_location */
	__u8 *hash_location;	/* temporary pointer, overloaded */
	__u32 tsval, tsecr;	/* need to include OPTION_TS */
	struct tcp_fastopen_cookie *fastopen_cookie;	/* Fast open cookie */
};

/* Write previously computed TCP options to the packet.
 *
 * Beware: Something in the Internet is very sensitive to the ordering of
 * TCP options, we learned this through the hard way, so be careful here.
 * Luckily we can at least blame others for their non-compliance but from
 * inter-operability perspective it seems that we're somewhat stuck with
 * the ordering which we have been using if we want to keep working with
 * those broken things (not that it currently hurts anybody as there isn't
 * particular reason why the ordering would need to be changed).
 *
 * At least SACK_PERM as the first option is known to lead to a disaster
 * (but it may well be that other scenarios fail similarly).
 */
static void tcp_options_write(__be32 *ptr, struct tcp_sock *tp,
			      struct tcp_out_options *opts)
{
	u16 options = opts->options;	/* mungable copy */

	if (unlikely(OPTION_MD5 & options)) {
		*ptr++ = htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16) |
			       (TCPOPT_MD5SIG << 8) | TCPOLEN_MD5SIG);
		/* overload cookie hash location */
		opts->hash_location = (__u8 *)ptr;
		ptr += 4;
	}

	if (unlikely(opts->mss)) {
		*ptr++ = htonl((TCPOPT_MSS << 24) |
			       (TCPOLEN_MSS << 16) |
			       opts->mss);
	}

	if (likely(OPTION_TS & options)) {
		if (unlikely(OPTION_SACK_ADVERTISE & options)) {
			*ptr++ = htonl((TCPOPT_SACK_PERM << 24) |
				       (TCPOLEN_SACK_PERM << 16) |
				       (TCPOPT_TIMESTAMP << 8) |
				       TCPOLEN_TIMESTAMP);
			options &= ~OPTION_SACK_ADVERTISE;
		} else {
			*ptr++ = htonl((TCPOPT_NOP << 24) |
				       (TCPOPT_NOP << 16) |
				       (TCPOPT_TIMESTAMP << 8) |
				       TCPOLEN_TIMESTAMP);
		}
		*ptr++ = htonl(opts->tsval);
		*ptr++ = htonl(opts->tsecr);
	}

	if (unlikely(OPTION_SACK_ADVERTISE & options)) {
		*ptr++ = htonl((TCPOPT_NOP << 24) |
			       (TCPOPT_NOP << 16) |
			       (TCPOPT_SACK_PERM << 8) |
			       TCPOLEN_SACK_PERM);
	}

	if (unlikely(OPTION_WSCALE & options)) {
		*ptr++ = htonl((TCPOPT_NOP << 24) |
			       (TCPOPT_WINDOW << 16) |
			       (TCPOLEN_WINDOW << 8) |
			       opts->ws);
	}

	if (unlikely(opts->num_sack_blocks)) {
		struct tcp_sack_block *sp = tp->rx_opt.dsack ?
			tp->duplicate_sack : tp->selective_acks;
		int this_sack;

		*ptr++ = htonl((TCPOPT_NOP  << 24) |
			       (TCPOPT_NOP  << 16) |
			       (TCPOPT_SACK <<  8) |
			       (TCPOLEN_SACK_BASE + (opts->num_sack_blocks *
						     TCPOLEN_SACK_PERBLOCK)));

		for (this_sack = 0; this_sack < opts->num_sack_blocks;
		     ++this_sack) {
			*ptr++ = htonl(sp[this_sack].start_seq);
			*ptr++ = htonl(sp[this_sack].end_seq);
		}

		tp->rx_opt.dsack = 0;
	}

	if (unlikely(OPTION_FAST_OPEN_COOKIE & options)) {
		struct tcp_fastopen_cookie *foc = opts->fastopen_cookie;

		*ptr++ = htonl((TCPOPT_EXP << 24) |
			       ((TCPOLEN_EXP_FASTOPEN_BASE + foc->len) << 16) |
			       TCPOPT_FASTOPEN_MAGIC);

		memcpy(ptr, foc->val, foc->len);
		if ((foc->len & 3) == 2) {
			u8 *align = ((u8 *)ptr) + foc->len;
			align[0] = align[1] = TCPOPT_NOP;
		}
		ptr += (foc->len + 3) >> 2;
	}
}

/* Compute TCP options for SYN packets. This is not the final
 * network wire format yet.
 */
static unsigned int tcp_syn_options(struct sock *sk, struct sk_buff *skb,
				struct tcp_out_options *opts,
				struct tcp_md5sig_key **md5)
{
	struct tcp_sock *tp = tcp_sk(sk);
	unsigned int remaining = MAX_TCP_OPTION_SPACE;
	struct tcp_fastopen_request *fastopen = tp->fastopen_req;

#ifdef CONFIG_TCP_MD5SIG
	*md5 = tp->af_specific->md5_lookup(sk, sk);
	if (*md5) {
		opts->options |= OPTION_MD5;
		remaining -= TCPOLEN_MD5SIG_ALIGNED;
	}
#else
	*md5 = NULL;
#endif

	/* We always get an MSS option.  The option bytes which will be seen in
	 * normal data packets should timestamps be used, must be in the MSS
	 * advertised.  But we subtract them from tp->mss_cache so that
	 * calculations in tcp_sendmsg are simpler etc.  So account for this
	 * fact here if necessary.  If we don't do this correctly, as a
	 * receiver we won't recognize data packets as being full sized when we
	 * should, and thus we won't abide by the delayed ACK rules correctly.
	 * SACKs don't matter, we never delay an ACK when we have any of those
	 * going out.  */
	opts->mss = tcp_advertise_mss(sk);
	remaining -= TCPOLEN_MSS_ALIGNED;

	if (likely(sysctl_tcp_timestamps && *md5 == NULL)) {
		opts->options |= OPTION_TS;
		opts->tsval = tcp_skb_timestamp(skb) + tp->tsoffset;
		opts->tsecr = tp->rx_opt.ts_recent;
		remaining -= TCPOLEN_TSTAMP_ALIGNED;
	}
	if (likely(sysctl_tcp_window_scaling)) {
		opts->ws = tp->rx_opt.rcv_wscale;
		opts->options |= OPTION_WSCALE;
		remaining -= TCPOLEN_WSCALE_ALIGNED;
	}
	if (likely(sysctl_tcp_sack)) {
		opts->options |= OPTION_SACK_ADVERTISE;
		if (unlikely(!(OPTION_TS & opts->options)))
			remaining -= TCPOLEN_SACKPERM_ALIGNED;
	}

	if (fastopen && fastopen->cookie.len >= 0) {
		u32 need = TCPOLEN_EXP_FASTOPEN_BASE + fastopen->cookie.len;
		need = (need + 3) & ~3U;  /* Align to 32 bits */
		if (remaining >= need) {
			opts->options |= OPTION_FAST_OPEN_COOKIE;
			opts->fastopen_cookie = &fastopen->cookie;
			remaining -= need;
			tp->syn_fastopen = 1;
		}
	}

	return MAX_TCP_OPTION_SPACE - remaining;
}

/* Set up TCP options for SYN-ACKs. */
static unsigned int tcp_synack_options(struct sock *sk,
				   struct request_sock *req,
				   unsigned int mss, struct sk_buff *skb,
				   struct tcp_out_options *opts,
				   struct tcp_md5sig_key **md5,
				   struct tcp_fastopen_cookie *foc)
{
	struct inet_request_sock *ireq = inet_rsk(req);
	unsigned int remaining = MAX_TCP_OPTION_SPACE;

#ifdef CONFIG_TCP_MD5SIG
	*md5 = tcp_rsk(req)->af_specific->md5_lookup(sk, req);
	if (*md5) {
		opts->options |= OPTION_MD5;
		remaining -= TCPOLEN_MD5SIG_ALIGNED;

		/* We can't fit any SACK blocks in a packet with MD5 + TS
		 * options. There was discussion about disabling SACK
		 * rather than TS in order to fit in better with old,
		 * buggy kernels, but that was deemed to be unnecessary.
		 */
		ireq->tstamp_ok &= !ireq->sack_ok;
	}
#else
	*md5 = NULL;
#endif

	/* We always send an MSS option. */
	opts->mss = mss;
	remaining -= TCPOLEN_MSS_ALIGNED;

	if (likely(ireq->wscale_ok)) {
		opts->ws = ireq->rcv_wscale;
		opts->options |= OPTION_WSCALE;
		remaining -= TCPOLEN_WSCALE_ALIGNED;
	}
	if (likely(ireq->tstamp_ok)) {
		opts->options |= OPTION_TS;
		opts->tsval = tcp_skb_timestamp(skb);
		opts->tsecr = req->ts_recent;
		remaining -= TCPOLEN_TSTAMP_ALIGNED;
	}
	if (likely(ireq->sack_ok)) {
		opts->options |= OPTION_SACK_ADVERTISE;
		if (unlikely(!ireq->tstamp_ok))
			remaining -= TCPOLEN_SACKPERM_ALIGNED;
	}
	if (foc != NULL && foc->len >= 0) {
		u32 need = TCPOLEN_EXP_FASTOPEN_BASE + foc->len;
		need = (need + 3) & ~3U;  /* Align to 32 bits */
		if (remaining >= need) {
			opts->options |= OPTION_FAST_OPEN_COOKIE;
			opts->fastopen_cookie = foc;
			remaining -= need;
		}
	}

	return MAX_TCP_OPTION_SPACE - remaining;
}

/* Compute TCP options for ESTABLISHED sockets. This is not the
 * final wire format yet.
 */
static unsigned int tcp_established_options(struct sock *sk, struct sk_buff *skb,
					struct tcp_out_options *opts,
					struct tcp_md5sig_key **md5)
{
	struct tcp_sock *tp = tcp_sk(sk);
	unsigned int size = 0;
	unsigned int eff_sacks;

	opts->options = 0;

#ifdef CONFIG_TCP_MD5SIG
	*md5 = tp->af_specific->md5_lookup(sk, sk);
	if (unlikely(*md5)) {
		opts->options |= OPTION_MD5;
		size += TCPOLEN_MD5SIG_ALIGNED;
	}
#else
	*md5 = NULL;
#endif

	if (likely(tp->rx_opt.tstamp_ok)) {
		opts->options |= OPTION_TS;
		opts->tsval = skb ? tcp_skb_timestamp(skb) + tp->tsoffset : 0;
		opts->tsecr = tp->rx_opt.ts_recent;
		size += TCPOLEN_TSTAMP_ALIGNED;
	}

	eff_sacks = tp->rx_opt.num_sacks + tp->rx_opt.dsack;
	if (unlikely(eff_sacks)) {
		const unsigned int remaining = MAX_TCP_OPTION_SPACE - size;
		opts->num_sack_blocks =
			min_t(unsigned int, eff_sacks,
			      (remaining - TCPOLEN_SACK_BASE_ALIGNED) /
			      TCPOLEN_SACK_PERBLOCK);
		size += TCPOLEN_SACK_BASE_ALIGNED +
			opts->num_sack_blocks * TCPOLEN_SACK_PERBLOCK;
	}

	return size;
}


/* TCP SMALL QUEUES (TSQ)
 *
 * TSQ goal is to keep small amount of skbs per tcp flow in tx queues (qdisc+dev)
 * to reduce RTT and bufferbloat.
 * We do this using a special skb destructor (tcp_wfree).
 *
 * Its important tcp_wfree() can be replaced by sock_wfree() in the event skb
 * needs to be reallocated in a driver.
 * The invariant being skb->truesize subtracted from sk->sk_wmem_alloc
 *
 * Since transmit from skb destructor is forbidden, we use a tasklet
 * to process all sockets that eventually need to send more skbs.
 * We use one tasklet per cpu, with its own queue of sockets.
 */
struct tsq_tasklet {
	struct tasklet_struct	tasklet;
	struct list_head	head; /* queue of tcp sockets */
};
static DEFINE_PER_CPU(struct tsq_tasklet, tsq_tasklet);

static void tcp_tsq_handler(struct sock *sk)
{
	if ((1 << sk->sk_state) &
	    (TCPF_ESTABLISHED | TCPF_FIN_WAIT1 | TCPF_CLOSING |
	     TCPF_CLOSE_WAIT  | TCPF_LAST_ACK))
		tcp_write_xmit(sk, tcp_current_mss(sk), tcp_sk(sk)->nonagle,
			       0, GFP_ATOMIC);
}
/*
 * One tasklet per cpu tries to send more skbs.
 * We run in tasklet context but need to disable irqs when
 * transferring tsq->head because tcp_wfree() might
 * interrupt us (non NAPI drivers)
 */
static void tcp_tasklet_func(unsigned long data)
{
	struct tsq_tasklet *tsq = (struct tsq_tasklet *)data;
	LIST_HEAD(list);
	unsigned long flags;
	struct list_head *q, *n;
	struct tcp_sock *tp;
	struct sock *sk;

	local_irq_save(flags);
	list_splice_init(&tsq->head, &list);
	local_irq_restore(flags);

	list_for_each_safe(q, n, &list) {
		tp = list_entry(q, struct tcp_sock, tsq_node);
		list_del(&tp->tsq_node);

		sk = (struct sock *)tp;
		bh_lock_sock(sk);

		if (!sock_owned_by_user(sk)) {
			tcp_tsq_handler(sk);
		} else {
			/* defer the work to tcp_release_cb() */
			set_bit(TCP_TSQ_DEFERRED, &tp->tsq_flags);
		}
		bh_unlock_sock(sk);

		clear_bit(TSQ_QUEUED, &tp->tsq_flags);
		sk_free(sk);
	}
}

#define TCP_DEFERRED_ALL ((1UL << TCP_TSQ_DEFERRED) |		\
			  (1UL << TCP_WRITE_TIMER_DEFERRED) |	\
			  (1UL << TCP_DELACK_TIMER_DEFERRED) |	\
			  (1UL << TCP_MTU_REDUCED_DEFERRED))
/**
 * tcp_release_cb - tcp release_sock() callback
 * @sk: socket
 *
 * called from release_sock() to perform protocol dependent
 * actions before socket release.
 */
void tcp_release_cb(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);
	unsigned long flags, nflags;

	/* perform an atomic operation only if at least one flag is set */
	do {
		flags = tp->tsq_flags;
		if (!(flags & TCP_DEFERRED_ALL))
			return;
		nflags = flags & ~TCP_DEFERRED_ALL;
	} while (cmpxchg(&tp->tsq_flags, flags, nflags) != flags);

	if (flags & (1UL << TCP_TSQ_DEFERRED))
		tcp_tsq_handler(sk);

	/* Here begins the tricky part :
	 * We are called from release_sock() with :
	 * 1) BH disabled
	 * 2) sk_lock.slock spinlock held
	 * 3) socket owned by us (sk->sk_lock.owned == 1)
	 *
	 * But following code is meant to be called from BH handlers,
	 * so we should keep BH disabled, but early release socket ownership
	 */
	sock_release_ownership(sk);

	if (flags & (1UL << TCP_WRITE_TIMER_DEFERRED)) {
		tcp_write_timer_handler(sk);
		__sock_put(sk);
	}
	if (flags & (1UL << TCP_DELACK_TIMER_DEFERRED)) {
		tcp_delack_timer_handler(sk);
		__sock_put(sk);
	}
	if (flags & (1UL << TCP_MTU_REDUCED_DEFERRED)) {
		inet_csk(sk)->icsk_af_ops->mtu_reduced(sk);
		__sock_put(sk);
	}
}
EXPORT_SYMBOL(tcp_release_cb);

void __init tcp_tasklet_init(void)
{
	int i;

	for_each_possible_cpu(i) {
		struct tsq_tasklet *tsq = &per_cpu(tsq_tasklet, i);

		INIT_LIST_HEAD(&tsq->head);
		tasklet_init(&tsq->tasklet,
			     tcp_tasklet_func,
			     (unsigned long)tsq);
	}
}

/*
 * Write buffer destructor automatically called from kfree_skb.
 * We can't xmit new skbs from this context, as we might already
 * hold qdisc lock.
 */
void tcp_wfree(struct sk_buff *skb)
{
	struct sock *sk = skb->sk;
	struct tcp_sock *tp = tcp_sk(sk);

	if (test_and_clear_bit(TSQ_THROTTLED, &tp->tsq_flags) &&
	    !test_and_set_bit(TSQ_QUEUED, &tp->tsq_flags)) {
		unsigned long flags;
		struct tsq_tasklet *tsq;

		/* Keep a ref on socket.
		 * This last ref will be released in tcp_tasklet_func()
		 */
		atomic_sub(skb->truesize - 1, &sk->sk_wmem_alloc);

		/* queue this socket to tasklet queue */
		local_irq_save(flags);
		tsq = &__get_cpu_var(tsq_tasklet);
		list_add(&tp->tsq_node, &tsq->head);
		tasklet_schedule(&tsq->tasklet);
		local_irq_restore(flags);
	} else {
		sock_wfree(skb);
	}
}

/* This routine actually transmits TCP packets queued in by
 * tcp_do_sendmsg().  This is used by both the initial
 * transmission and possible later retransmissions.
 * All SKB's seen here are completely headerless.  It is our
 * job to build the TCP header, and pass the packet down to
 * IP so it can do the same plus pass the packet off to the
 * device.
 *
 * We are working here with either a clone of the original
 * SKB, or a fresh unique copy made by the retransmit engine.
 */
static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
			    gfp_t gfp_mask)
{
	const struct inet_connection_sock *icsk = inet_csk(sk);
	struct inet_sock *inet;
	struct tcp_sock *tp;
	struct tcp_skb_cb *tcb;
	struct tcp_out_options opts;
	unsigned int tcp_options_size, tcp_header_size;
	struct tcp_md5sig_key *md5;
	struct tcphdr *th;
	int err;

	BUG_ON(!skb || !tcp_skb_pcount(skb));

	if (clone_it) {
		skb_mstamp_get(&skb->skb_mstamp);

		if (unlikely(skb_cloned(skb)))
			skb = pskb_copy(skb, gfp_mask);
		else
			skb = skb_clone(skb, gfp_mask);
		if (unlikely(!skb))
			return -ENOBUFS;
	}

	inet = inet_sk(sk);
	tp = tcp_sk(sk);
	tcb = TCP_SKB_CB(skb);
	memset(&opts, 0, sizeof(opts));

	if (unlikely(tcb->tcp_flags & TCPHDR_SYN))
		tcp_options_size = tcp_syn_options(sk, skb, &opts, &md5);
	else
		tcp_options_size = tcp_established_options(sk, skb, &opts,
							   &md5);
	tcp_header_size = tcp_options_size + sizeof(struct tcphdr);

	if (tcp_packets_in_flight(tp) == 0)
		tcp_ca_event(sk, CA_EVENT_TX_START);

	/* if no packet is in qdisc/device queue, then allow XPS to select
	 * another queue. We can be called from tcp_tsq_handler()
	 * which holds one reference to sk_wmem_alloc.
	 *
	 * TODO: Ideally, in-flight pure ACK packets should not matter here.
	 * One way to get this would be to set skb->truesize = 2 on them.
	 */
	skb->ooo_okay = sk_wmem_alloc_get(sk) < SKB_TRUESIZE(1);

	skb_push(skb, tcp_header_size);
	skb_reset_transport_header(skb);

	skb_orphan(skb);
	skb->sk = sk;
	skb->destructor = tcp_wfree;
	skb_set_hash_from_sk(skb, sk);
	atomic_add(skb->truesize, &sk->sk_wmem_alloc);

	/* Build TCP header and checksum it. */
	th = tcp_hdr(skb);
	th->source		= inet->inet_sport;
	th->dest		= inet->inet_dport;
	th->seq			= htonl(tcb->seq);
	th->ack_seq		= htonl(tp->rcv_nxt);
	*(((__be16 *)th) + 6)	= htons(((tcp_header_size >> 2) << 12) |
					tcb->tcp_flags);

	if (unlikely(tcb->tcp_flags & TCPHDR_SYN)) {
		/* RFC1323: The window in SYN & SYN/ACK segments
		 * is never scaled.
		 */
		th->window	= htons(min(tp->rcv_wnd, 65535U));
	} else {
		th->window	= htons(tcp_select_window(sk));
	}
	th->check		= 0;
	th->urg_ptr		= 0;

	/* The urg_mode check is necessary during a below snd_una win probe */
	if (unlikely(tcp_urg_mode(tp) && before(tcb->seq, tp->snd_up))) {
		if (before(tp->snd_up, tcb->seq + 0x10000)) {
			th->urg_ptr = htons(tp->snd_up - tcb->seq);
			th->urg = 1;
		} else if (after(tcb->seq + 0xFFFF, tp->snd_nxt)) {
			th->urg_ptr = htons(0xFFFF);
			th->urg = 1;
		}
	}

	tcp_options_write((__be32 *)(th + 1), tp, &opts);
	if (likely((tcb->tcp_flags & TCPHDR_SYN) == 0))
		tcp_ecn_send(sk, skb, tcp_header_size);

#ifdef CONFIG_TCP_MD5SIG
	/* Calculate the MD5 hash, as we have all we need now */
	if (md5) {
		sk_nocaps_add(sk, NETIF_F_GSO_MASK);
		tp->af_specific->calc_md5_hash(opts.hash_location,
					       md5, sk, NULL, skb);
	}
#endif

	icsk->icsk_af_ops->send_check(sk, skb);

	if (likely(tcb->tcp_flags & TCPHDR_ACK))
		tcp_event_ack_sent(sk, tcp_skb_pcount(skb));

	if (skb->len != tcp_header_size)
		tcp_event_data_sent(tp, sk);

	if (after(tcb->end_seq, tp->snd_nxt) || tcb->seq == tcb->end_seq)
		TCP_ADD_STATS(sock_net(sk), TCP_MIB_OUTSEGS,
			      tcp_skb_pcount(skb));

	/* OK, its time to fill skb_shinfo(skb)->gso_segs */
	skb_shinfo(skb)->gso_segs = tcp_skb_pcount(skb);

	/* Our usage of tstamp should remain private */
	skb->tstamp.tv64 = 0;

	/* Cleanup our debris for IP stacks */
	memset(skb->cb, 0, max(sizeof(struct inet_skb_parm),
			       sizeof(struct inet6_skb_parm)));

	err = icsk->icsk_af_ops->queue_xmit(sk, skb, &inet->cork.fl);

	if (likely(err <= 0))
		return err;

	tcp_enter_cwr(sk);

	return net_xmit_eval(err);
}

/* This routine just queues the buffer for sending.
 *
 * NOTE: probe0 timer is not checked, do not forget tcp_push_pending_frames,
 * otherwise socket can stall.
 */
static void tcp_queue_skb(struct sock *sk, struct sk_buff *skb)
{
	struct tcp_sock *tp = tcp_sk(sk);

	/* Advance write_seq and place onto the write_queue. */
	tp->write_seq = TCP_SKB_CB(skb)->end_seq;
	__skb_header_release(skb);
	tcp_add_write_queue_tail(sk, skb);
	sk->sk_wmem_queued += skb->truesize;
	sk_mem_charge(sk, skb->truesize);
}

/* Initialize TSO segments for a packet. */
static void tcp_set_skb_tso_segs(const struct sock *sk, struct sk_buff *skb,
				 unsigned int mss_now)
{
	struct skb_shared_info *shinfo = skb_shinfo(skb);

	/* Make sure we own this skb before messing gso_size/gso_segs */
	WARN_ON_ONCE(skb_cloned(skb));

	if (skb->len <= mss_now || skb->ip_summed == CHECKSUM_NONE) {
		/* Avoid the costly divide in the normal
		 * non-TSO case.
		 */
		tcp_skb_pcount_set(skb, 1);
		shinfo->gso_size = 0;
		shinfo->gso_type = 0;
	} else {
		tcp_skb_pcount_set(skb, DIV_ROUND_UP(skb->len, mss_now));
		shinfo->gso_size = mss_now;
		shinfo->gso_type = sk->sk_gso_type;
	}
}

/* When a modification to fackets out becomes necessary, we need to check
 * skb is counted to fackets_out or not.
 */
static void tcp_adjust_fackets_out(struct sock *sk, const struct sk_buff *skb,
				   int decr)
{
	struct tcp_sock *tp = tcp_sk(sk);

	if (!tp->sacked_out || tcp_is_reno(tp))
		return;

	if (after(tcp_highest_sack_seq(tp), TCP_SKB_CB(skb)->seq))
		tp->fackets_out -= decr;
}

/* Pcount in the middle of the write queue got changed, we need to do various
 * tweaks to fix counters
 */
static void tcp_adjust_pcount(struct sock *sk, const struct sk_buff *skb, int decr)
{
	struct tcp_sock *tp = tcp_sk(sk);

	tp->packets_out -= decr;

	if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
		tp->sacked_out -= decr;
	if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS)
		tp->retrans_out -= decr;
	if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST)
		tp->lost_out -= decr;

	/* Reno case is special. Sigh... */
	if (tcp_is_reno(tp) && decr > 0)
		tp->sacked_out -= min_t(u32, tp->sacked_out, decr);

	tcp_adjust_fackets_out(sk, skb, decr);

	if (tp->lost_skb_hint &&
	    before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(tp->lost_skb_hint)->seq) &&
	    (tcp_is_fack(tp) || (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)))
		tp->lost_cnt_hint -= decr;

	tcp_verify_left_out(tp);
}

static void tcp_fragment_tstamp(struct sk_buff *skb, struct sk_buff *skb2)
{
	struct skb_shared_info *shinfo = skb_shinfo(skb);

	if (unlikely(shinfo->tx_flags & SKBTX_ANY_TSTAMP) &&
	    !before(shinfo->tskey, TCP_SKB_CB(skb2)->seq)) {
		struct skb_shared_info *shinfo2 = skb_shinfo(skb2);
		u8 tsflags = shinfo->tx_flags & SKBTX_ANY_TSTAMP;

		shinfo->tx_flags &= ~tsflags;
		shinfo2->tx_flags |= tsflags;
		swap(shinfo->tskey, shinfo2->tskey);
	}
}

/* Function to create two new TCP segments.  Shrinks the given segment
 * to the specified size and appends a new segment with the rest of the
 * packet to the list.  This won't be called frequently, I hope.
 * Remember, these are still headerless SKBs at this point.
 */
int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len,
		 unsigned int mss_now, gfp_t gfp)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *buff;
	int nsize, old_factor;
	int nlen;
	u8 flags;

	if (WARN_ON(len > skb->len))
		return -EINVAL;

	nsize = skb_headlen(skb) - len;
	if (nsize < 0)
		nsize = 0;

	if (skb_unclone(skb, gfp))
		return -ENOMEM;

	/* Get a new skb... force flag on. */
	buff = sk_stream_alloc_skb(sk, nsize, gfp);
	if (buff == NULL)
		return -ENOMEM; /* We'll just try again later. */

	sk->sk_wmem_queued += buff->truesize;
	sk_mem_charge(sk, buff->truesize);
	nlen = skb->len - len - nsize;
	buff->truesize += nlen;
	skb->truesize -= nlen;

	/* Correct the sequence numbers. */
	TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
	TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
	TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;

	/* PSH and FIN should only be set in the second packet. */
	flags = TCP_SKB_CB(skb)->tcp_flags;
	TCP_SKB_CB(skb)->tcp_flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH);
	TCP_SKB_CB(buff)->tcp_flags = flags;
	TCP_SKB_CB(buff)->sacked = TCP_SKB_CB(skb)->sacked;

	if (!skb_shinfo(skb)->nr_frags && skb->ip_summed != CHECKSUM_PARTIAL) {
		/* Copy and checksum data tail into the new buffer. */
		buff->csum = csum_partial_copy_nocheck(skb->data + len,
						       skb_put(buff, nsize),
						       nsize, 0);

		skb_trim(skb, len);

		skb->csum = csum_block_sub(skb->csum, buff->csum, len);
	} else {
		skb->ip_summed = CHECKSUM_PARTIAL;
		skb_split(skb, buff, len);
	}

	buff->ip_summed = skb->ip_summed;

	buff->tstamp = skb->tstamp;
	tcp_fragment_tstamp(skb, buff);

	old_factor = tcp_skb_pcount(skb);

	/* Fix up tso_factor for both original and new SKB.  */
	tcp_set_skb_tso_segs(sk, skb, mss_now);
	tcp_set_skb_tso_segs(sk, buff, mss_now);

	/* If this packet has been sent out already, we must
	 * adjust the various packet counters.
	 */
	if (!before(tp->snd_nxt, TCP_SKB_CB(buff)->end_seq)) {
		int diff = old_factor - tcp_skb_pcount(skb) -
			tcp_skb_pcount(buff);

		if (diff)
			tcp_adjust_pcount(sk, skb, diff);
	}

	/* Link BUFF into the send queue. */
	__skb_header_release(buff);
	tcp_insert_write_queue_after(skb, buff, sk);

	return 0;
}

/* This is similar to __pskb_pull_head() (it will go to core/skbuff.c
 * eventually). The difference is that pulled data not copied, but
 * immediately discarded.
 */
static void __pskb_trim_head(struct sk_buff *skb, int len)
{
	struct skb_shared_info *shinfo;
	int i, k, eat;

	eat = min_t(int, len, skb_headlen(skb));
	if (eat) {
		__skb_pull(skb, eat);
		len -= eat;
		if (!len)
			return;
	}
	eat = len;
	k = 0;
	shinfo = skb_shinfo(skb);
	for (i = 0; i < shinfo->nr_frags; i++) {
		int size = skb_frag_size(&shinfo->frags[i]);

		if (size <= eat) {
			skb_frag_unref(skb, i);
			eat -= size;
		} else {
			shinfo->frags[k] = shinfo->frags[i];
			if (eat) {
				shinfo->frags[k].page_offset += eat;
				skb_frag_size_sub(&shinfo->frags[k], eat);
				eat = 0;
			}
			k++;
		}
	}
	shinfo->nr_frags = k;

	skb_reset_tail_pointer(skb);
	skb->data_len -= len;
	skb->len = skb->data_len;
}

/* Remove acked data from a packet in the transmit queue. */
int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len)
{
	if (skb_unclone(skb, GFP_ATOMIC))
		return -ENOMEM;

	__pskb_trim_head(skb, len);

	TCP_SKB_CB(skb)->seq += len;
	skb->ip_summed = CHECKSUM_PARTIAL;

	skb->truesize	     -= len;
	sk->sk_wmem_queued   -= len;
	sk_mem_uncharge(sk, len);
	sock_set_flag(sk, SOCK_QUEUE_SHRUNK);

	/* Any change of skb->len requires recalculation of tso factor. */
	if (tcp_skb_pcount(skb) > 1)
		tcp_set_skb_tso_segs(sk, skb, tcp_skb_mss(skb));

	return 0;
}

/* Calculate MSS not accounting any TCP options.  */
static inline int __tcp_mtu_to_mss(struct sock *sk, int pmtu)
{
	const struct tcp_sock *tp = tcp_sk(sk);
	const struct inet_connection_sock *icsk = inet_csk(sk);
	int mss_now;

	/* Calculate base mss without TCP options:
	   It is MMS_S - sizeof(tcphdr) of rfc1122
	 */
	mss_now = pmtu - icsk->icsk_af_ops->net_header_len - sizeof(struct tcphdr);

	/* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
	if (icsk->icsk_af_ops->net_frag_header_len) {
		const struct dst_entry *dst = __sk_dst_get(sk);

		if (dst && dst_allfrag(dst))
			mss_now -= icsk->icsk_af_ops->net_frag_header_len;
	}

	/* Clamp it (mss_clamp does not include tcp options) */
	if (mss_now > tp->rx_opt.mss_clamp)
		mss_now = tp->rx_opt.mss_clamp;

	/* Now subtract optional transport overhead */
	mss_now -= icsk->icsk_ext_hdr_len;

	/* Then reserve room for full set of TCP options and 8 bytes of data */
	if (mss_now < 48)
		mss_now = 48;
	return mss_now;
}

/* Calculate MSS. Not accounting for SACKs here.  */
int tcp_mtu_to_mss(struct sock *sk, int pmtu)
{
	/* Subtract TCP options size, not including SACKs */
	return __tcp_mtu_to_mss(sk, pmtu) -
	       (tcp_sk(sk)->tcp_header_len - sizeof(struct tcphdr));
}

/* Inverse of above */
int tcp_mss_to_mtu(struct sock *sk, int mss)
{
	const struct tcp_sock *tp = tcp_sk(sk);
	const struct inet_connection_sock *icsk = inet_csk(sk);
	int mtu;

	mtu = mss +
	      tp->tcp_header_len +
	      icsk->icsk_ext_hdr_len +
	      icsk->icsk_af_ops->net_header_len;

	/* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
	if (icsk->icsk_af_ops->net_frag_header_len) {
		const struct dst_entry *dst = __sk_dst_get(sk);

		if (dst && dst_allfrag(dst))
			mtu += icsk->icsk_af_ops->net_frag_header_len;
	}
	return mtu;
}

/* MTU probing init per socket */
void tcp_mtup_init(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct inet_connection_sock *icsk = inet_csk(sk);

	icsk->icsk_mtup.enabled = sysctl_tcp_mtu_probing > 1;
	icsk->icsk_mtup.search_high = tp->rx_opt.mss_clamp + sizeof(struct tcphdr) +
			       icsk->icsk_af_ops->net_header_len;
	icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, sysctl_tcp_base_mss);
	icsk->icsk_mtup.probe_size = 0;
}
EXPORT_SYMBOL(tcp_mtup_init);

/* This function synchronize snd mss to current pmtu/exthdr set.

   tp->rx_opt.user_mss is mss set by user by TCP_MAXSEG. It does NOT counts
   for TCP options, but includes only bare TCP header.

   tp->rx_opt.mss_clamp is mss negotiated at connection setup.
   It is minimum of user_mss and mss received with SYN.
   It also does not include TCP options.

   inet_csk(sk)->icsk_pmtu_cookie is last pmtu, seen by this function.

   tp->mss_cache is current effective sending mss, including
   all tcp options except for SACKs. It is evaluated,
   taking into account current pmtu, but never exceeds
   tp->rx_opt.mss_clamp.

   NOTE1. rfc1122 clearly states that advertised MSS
   DOES NOT include either tcp or ip options.

   NOTE2. inet_csk(sk)->icsk_pmtu_cookie and tp->mss_cache
   are READ ONLY outside this function.		--ANK (980731)
 */
unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct inet_connection_sock *icsk = inet_csk(sk);
	int mss_now;

	if (icsk->icsk_mtup.search_high > pmtu)
		icsk->icsk_mtup.search_high = pmtu;

	mss_now = tcp_mtu_to_mss(sk, pmtu);
	mss_now = tcp_bound_to_half_wnd(tp, mss_now);

	/* And store cached results */
	icsk->icsk_pmtu_cookie = pmtu;
	if (icsk->icsk_mtup.enabled)
		mss_now = min(mss_now, tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low));
	tp->mss_cache = mss_now;

	return mss_now;
}
EXPORT_SYMBOL(tcp_sync_mss);

/* Compute the current effective MSS, taking SACKs and IP options,
 * and even PMTU discovery events into account.
 */
unsigned int tcp_current_mss(struct sock *sk)
{
	const struct tcp_sock *tp = tcp_sk(sk);
	const struct dst_entry *dst = __sk_dst_get(sk);
	u32 mss_now;
	unsigned int header_len;
	struct tcp_out_options opts;
	struct tcp_md5sig_key *md5;

	mss_now = tp->mss_cache;

	if (dst) {
		u32 mtu = dst_mtu(dst);
		if (mtu != inet_csk(sk)->icsk_pmtu_cookie)
			mss_now = tcp_sync_mss(sk, mtu);
	}

	header_len = tcp_established_options(sk, NULL, &opts, &md5) +
		     sizeof(struct tcphdr);
	/* The mss_cache is sized based on tp->tcp_header_len, which assumes
	 * some common options. If this is an odd packet (because we have SACK
	 * blocks etc) then our calculated header_len will be different, and
	 * we have to adjust mss_now correspondingly */
	if (header_len != tp->tcp_header_len) {
		int delta = (int) header_len - tp->tcp_header_len;
		mss_now -= delta;
	}

	return mss_now;
}

/* RFC2861, slow part. Adjust cwnd, after it was not full during one rto.
 * As additional protections, we do not touch cwnd in retransmission phases,
 * and if application hit its sndbuf limit recently.
 */
static void tcp_cwnd_application_limited(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);

	if (inet_csk(sk)->icsk_ca_state == TCP_CA_Open &&
	    sk->sk_socket && !test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
		/* Limited by application or receiver window. */
		u32 init_win = tcp_init_cwnd(tp, __sk_dst_get(sk));
		u32 win_used = max(tp->snd_cwnd_used, init_win);
		if (win_used < tp->snd_cwnd) {
			tp->snd_ssthresh = tcp_current_ssthresh(sk);
			tp->snd_cwnd = (tp->snd_cwnd + win_used) >> 1;
		}
		tp->snd_cwnd_used = 0;
	}
	tp->snd_cwnd_stamp = tcp_time_stamp;
}

static void tcp_cwnd_validate(struct sock *sk, bool is_cwnd_limited)
{
	struct tcp_sock *tp = tcp_sk(sk);

	/* Track the maximum number of outstanding packets in each
	 * window, and remember whether we were cwnd-limited then.
	 */
	if (!before(tp->snd_una, tp->max_packets_seq) ||
	    tp->packets_out > tp->max_packets_out) {
		tp->max_packets_out = tp->packets_out;
		tp->max_packets_seq = tp->snd_nxt;
		tp->is_cwnd_limited = is_cwnd_limited;
	}

	if (tcp_is_cwnd_limited(sk)) {
		/* Network is feed fully. */
		tp->snd_cwnd_used = 0;
		tp->snd_cwnd_stamp = tcp_time_stamp;
	} else {
		/* Network starves. */
		if (tp->packets_out > tp->snd_cwnd_used)
			tp->snd_cwnd_used = tp->packets_out;

		if (sysctl_tcp_slow_start_after_idle &&
		    (s32)(tcp_time_stamp - tp->snd_cwnd_stamp) >= inet_csk(sk)->icsk_rto)
			tcp_cwnd_application_limited(sk);
	}
}

/* Minshall's variant of the Nagle send check. */
static bool tcp_minshall_check(const struct tcp_sock *tp)
{
	return after(tp->snd_sml, tp->snd_una) &&
		!after(tp->snd_sml, tp->snd_nxt);
}

/* Update snd_sml if this skb is under mss
 * Note that a TSO packet might end with a sub-mss segment
 * The test is really :
 * if ((skb->len % mss) != 0)
 *        tp->snd_sml = TCP_SKB_CB(skb)->end_seq;
 * But we can avoid doing the divide again given we already have
 *  skb_pcount = skb->len / mss_now
 */
static void tcp_minshall_update(struct tcp_sock *tp, unsigned int mss_now,
				const struct sk_buff *skb)
{
	if (skb->len < tcp_skb_pcount(skb) * mss_now)
		tp->snd_sml = TCP_SKB_CB(skb)->end_seq;
}

/* Return false, if packet can be sent now without violation Nagle's rules:
 * 1. It is full sized. (provided by caller in %partial bool)
 * 2. Or it contains FIN. (already checked by caller)
 * 3. Or TCP_CORK is not set, and TCP_NODELAY is set.
 * 4. Or TCP_CORK is not set, and all sent packets are ACKed.
 *    With Minshall's modification: all sent small packets are ACKed.
 */
static bool tcp_nagle_check(bool partial, const struct tcp_sock *tp,
			    int nonagle)
{
	return partial &&
		((nonagle & TCP_NAGLE_CORK) ||
		 (!nonagle && tp->packets_out && tcp_minshall_check(tp)));
}
/* Returns the portion of skb which can be sent right away */
static unsigned int tcp_mss_split_point(const struct sock *sk,
					const struct sk_buff *skb,
					unsigned int mss_now,
					unsigned int max_segs,
					int nonagle)
{
	const struct tcp_sock *tp = tcp_sk(sk);
	u32 partial, needed, window, max_len;

	window = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
	max_len = mss_now * max_segs;

	if (likely(max_len <= window && skb != tcp_write_queue_tail(sk)))
		return max_len;

	needed = min(skb->len, window);

	if (max_len <= needed)
		return max_len;

	partial = needed % mss_now;
	/* If last segment is not a full MSS, check if Nagle rules allow us
	 * to include this last segment in this skb.
	 * Otherwise, we'll split the skb at last MSS boundary
	 */
	if (tcp_nagle_check(partial != 0, tp, nonagle))
		return needed - partial;

	return needed;
}

/* Can at least one segment of SKB be sent right now, according to the
 * congestion window rules?  If so, return how many segments are allowed.
 */
static inline unsigned int tcp_cwnd_test(const struct tcp_sock *tp,
					 const struct sk_buff *skb)
{
	u32 in_flight, cwnd;

	/* Don't be strict about the congestion window for the final FIN.  */
	if ((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) &&
	    tcp_skb_pcount(skb) == 1)
		return 1;

	in_flight = tcp_packets_in_flight(tp);
	cwnd = tp->snd_cwnd;
	if (in_flight < cwnd)
		return (cwnd - in_flight);

	return 0;
}

/* Initialize TSO state of a skb.
 * This must be invoked the first time we consider transmitting
 * SKB onto the wire.
 */
static int tcp_init_tso_segs(const struct sock *sk, struct sk_buff *skb,
			     unsigned int mss_now)
{
	int tso_segs = tcp_skb_pcount(skb);

	if (!tso_segs || (tso_segs > 1 && tcp_skb_mss(skb) != mss_now)) {
		tcp_set_skb_tso_segs(sk, skb, mss_now);
		tso_segs = tcp_skb_pcount(skb);
	}
	return tso_segs;
}


/* Return true if the Nagle test allows this packet to be
 * sent now.
 */
static inline bool tcp_nagle_test(const struct tcp_sock *tp, const struct sk_buff *skb,
				  unsigned int cur_mss, int nonagle)
{
	/* Nagle rule does not apply to frames, which sit in the middle of the
	 * write_queue (they have no chances to get new data).
	 *
	 * This is implemented in the callers, where they modify the 'nonagle'
	 * argument based upon the location of SKB in the send queue.
	 */
	if (nonagle & TCP_NAGLE_PUSH)
		return true;

	/* Don't use the nagle rule for urgent data (or for the final FIN). */
	if (tcp_urg_mode(tp) || (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN))
		return true;

	if (!tcp_nagle_check(skb->len < cur_mss, tp, nonagle))
		return true;

	return false;
}

/* Does at least the first segment of SKB fit into the send window? */
static bool tcp_snd_wnd_test(const struct tcp_sock *tp,
			     const struct sk_buff *skb,
			     unsigned int cur_mss)
{
	u32 end_seq = TCP_SKB_CB(skb)->end_seq;

	if (skb->len > cur_mss)
		end_seq = TCP_SKB_CB(skb)->seq + cur_mss;

	return !after(end_seq, tcp_wnd_end(tp));
}

/* This checks if the data bearing packet SKB (usually tcp_send_head(sk))
 * should be put on the wire right now.  If so, it returns the number of
 * packets allowed by the congestion window.
 */
static unsigned int tcp_snd_test(const struct sock *sk, struct sk_buff *skb,
				 unsigned int cur_mss, int nonagle)
{
	const struct tcp_sock *tp = tcp_sk(sk);
	unsigned int cwnd_quota;

	tcp_init_tso_segs(sk, skb, cur_mss);

	if (!tcp_nagle_test(tp, skb, cur_mss, nonagle))
		return 0;

	cwnd_quota = tcp_cwnd_test(tp, skb);
	if (cwnd_quota && !tcp_snd_wnd_test(tp, skb, cur_mss))
		cwnd_quota = 0;

	return cwnd_quota;
}

/* Test if sending is allowed right now. */
bool tcp_may_send_now(struct sock *sk)
{
	const struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *skb = tcp_send_head(sk);

	return skb &&
		tcp_snd_test(sk, skb, tcp_current_mss(sk),
			     (tcp_skb_is_last(sk, skb) ?
			      tp->nonagle : TCP_NAGLE_PUSH));
}

/* Trim TSO SKB to LEN bytes, put the remaining data into a new packet
 * which is put after SKB on the list.  It is very much like
 * tcp_fragment() except that it may make several kinds of assumptions
 * in order to speed up the splitting operation.  In particular, we
 * know that all the data is in scatter-gather pages, and that the
 * packet has never been sent out before (and thus is not cloned).
 */
static int tso_fragment(struct sock *sk, struct sk_buff *skb, unsigned int len,
			unsigned int mss_now, gfp_t gfp)
{
	struct sk_buff *buff;
	int nlen = skb->len - len;
	u8 flags;

	/* All of a TSO frame must be composed of paged data.  */
	if (skb->len != skb->data_len)
		return tcp_fragment(sk, skb, len, mss_now, gfp);

	buff = sk_stream_alloc_skb(sk, 0, gfp);
	if (unlikely(buff == NULL))
		return -ENOMEM;

	sk->sk_wmem_queued += buff->truesize;
	sk_mem_charge(sk, buff->truesize);
	buff->truesize += nlen;
	skb->truesize -= nlen;

	/* Correct the sequence numbers. */
	TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
	TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
	TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;

	/* PSH and FIN should only be set in the second packet. */
	flags = TCP_SKB_CB(skb)->tcp_flags;
	TCP_SKB_CB(skb)->tcp_flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH);
	TCP_SKB_CB(buff)->tcp_flags = flags;

	/* This packet was never sent out yet, so no SACK bits. */
	TCP_SKB_CB(buff)->sacked = 0;

	buff->ip_summed = skb->ip_summed = CHECKSUM_PARTIAL;
	skb_split(skb, buff, len);
	tcp_fragment_tstamp(skb, buff);

	/* Fix up tso_factor for both original and new SKB.  */
	tcp_set_skb_tso_segs(sk, skb, mss_now);
	tcp_set_skb_tso_segs(sk, buff, mss_now);

	/* Link BUFF into the send queue. */
	__skb_header_release(buff);
	tcp_insert_write_queue_after(skb, buff, sk);

	return 0;
}

/* Try to defer sending, if possible, in order to minimize the amount
 * of TSO splitting we do.  View it as a kind of TSO Nagle test.
 *
 * This algorithm is from John Heffner.
 */
static bool tcp_tso_should_defer(struct sock *sk, struct sk_buff *skb,
				 bool *is_cwnd_limited)
{
	struct tcp_sock *tp = tcp_sk(sk);
	const struct inet_connection_sock *icsk = inet_csk(sk);
	u32 send_win, cong_win, limit, in_flight;
	int win_divisor;

	if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
		goto send_now;

	if (icsk->icsk_ca_state != TCP_CA_Open)
		goto send_now;

	/* Defer for less than two clock ticks. */
	if (tp->tso_deferred &&
	    (((u32)jiffies << 1) >> 1) - (tp->tso_deferred >> 1) > 1)
		goto send_now;

	in_flight = tcp_packets_in_flight(tp);

	BUG_ON(tcp_skb_pcount(skb) <= 1 || (tp->snd_cwnd <= in_flight));

	send_win = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;

	/* From in_flight test above, we know that cwnd > in_flight.  */
	cong_win = (tp->snd_cwnd - in_flight) * tp->mss_cache;

	limit = min(send_win, cong_win);

	/* If a full-sized TSO skb can be sent, do it. */
	if (limit >= min_t(unsigned int, sk->sk_gso_max_size,
			   tp->xmit_size_goal_segs * tp->mss_cache))
		goto send_now;

	/* Middle in queue won't get any more data, full sendable already? */
	if ((skb != tcp_write_queue_tail(sk)) && (limit >= skb->len))
		goto send_now;

	win_divisor = ACCESS_ONCE(sysctl_tcp_tso_win_divisor);
	if (win_divisor) {
		u32 chunk = min(tp->snd_wnd, tp->snd_cwnd * tp->mss_cache);

		/* If at least some fraction of a window is available,
		 * just use it.
		 */
		chunk /= win_divisor;
		if (limit >= chunk)
			goto send_now;
	} else {
		/* Different approach, try not to defer past a single
		 * ACK.  Receiver should ACK every other full sized
		 * frame, so if we have space for more than 3 frames
		 * then send now.
		 */
		if (limit > tcp_max_tso_deferred_mss(tp) * tp->mss_cache)
			goto send_now;
	}

	/* Ok, it looks like it is advisable to defer.
	 * Do not rearm the timer if already set to not break TCP ACK clocking.
	 */
	if (!tp->tso_deferred)
		tp->tso_deferred = 1 | (jiffies << 1);

	if (cong_win < send_win && cong_win < skb->len)
		*is_cwnd_limited = true;

	return true;

send_now:
	tp->tso_deferred = 0;
	return false;
}

/* Create a new MTU probe if we are ready.
 * MTU probe is regularly attempting to increase the path MTU by
 * deliberately sending larger packets.  This discovers routing
 * changes resulting in larger path MTUs.
 *
 * Returns 0 if we should wait to probe (no cwnd available),
 *         1 if a probe was sent,
 *         -1 otherwise
 */
static int tcp_mtu_probe(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct inet_connection_sock *icsk = inet_csk(sk);
	struct sk_buff *skb, *nskb, *next;
	int len;
	int probe_size;
	int size_needed;
	int copy;
	int mss_now;

	/* Not currently probing/verifying,
	 * not in recovery,
	 * have enough cwnd, and
	 * not SACKing (the variable headers throw things off) */
	if (!icsk->icsk_mtup.enabled ||
	    icsk->icsk_mtup.probe_size ||
	    inet_csk(sk)->icsk_ca_state != TCP_CA_Open ||
	    tp->snd_cwnd < 11 ||
	    tp->rx_opt.num_sacks || tp->rx_opt.dsack)
		return -1;

	/* Very simple search strategy: just double the MSS. */
	mss_now = tcp_current_mss(sk);
	probe_size = 2 * tp->mss_cache;
	size_needed = probe_size + (tp->reordering + 1) * tp->mss_cache;
	if (probe_size > tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_high)) {
		/* TODO: set timer for probe_converge_event */
		return -1;
	}

	/* Have enough data in the send queue to probe? */
	if (tp->write_seq - tp->snd_nxt < size_needed)
		return -1;

	if (tp->snd_wnd < size_needed)
		return -1;
	if (after(tp->snd_nxt + size_needed, tcp_wnd_end(tp)))
		return 0;

	/* Do we need to wait to drain cwnd? With none in flight, don't stall */
	if (tcp_packets_in_flight(tp) + 2 > tp->snd_cwnd) {
		if (!tcp_packets_in_flight(tp))
			return -1;
		else
			return 0;
	}

	/* We're allowed to probe.  Build it now. */
	if ((nskb = sk_stream_alloc_skb(sk, probe_size, GFP_ATOMIC)) == NULL)
		return -1;
	sk->sk_wmem_queued += nskb->truesize;
	sk_mem_charge(sk, nskb->truesize);

	skb = tcp_send_head(sk);

	TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(skb)->seq;
	TCP_SKB_CB(nskb)->end_seq = TCP_SKB_CB(skb)->seq + probe_size;
	TCP_SKB_CB(nskb)->tcp_flags = TCPHDR_ACK;
	TCP_SKB_CB(nskb)->sacked = 0;
	nskb->csum = 0;
	nskb->ip_summed = skb->ip_summed;

	tcp_insert_write_queue_before(nskb, skb, sk);

	len = 0;
	tcp_for_write_queue_from_safe(skb, next, sk) {
		copy = min_t(int, skb->len, probe_size - len);
		if (nskb->ip_summed)
			skb_copy_bits(skb, 0, skb_put(nskb, copy), copy);
		else
			nskb->csum = skb_copy_and_csum_bits(skb, 0,
							    skb_put(nskb, copy),
							    copy, nskb->csum);

		if (skb->len <= copy) {
			/* We've eaten all the data from this skb.
			 * Throw it away. */
			TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags;
			tcp_unlink_write_queue(skb, sk);
			sk_wmem_free_skb(sk, skb);
		} else {
			TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags &
						   ~(TCPHDR_FIN|TCPHDR_PSH);
			if (!skb_shinfo(skb)->nr_frags) {
				skb_pull(skb, copy);
				if (skb->ip_summed != CHECKSUM_PARTIAL)
					skb->csum = csum_partial(skb->data,
								 skb->len, 0);
			} else {
				__pskb_trim_head(skb, copy);
				tcp_set_skb_tso_segs(sk, skb, mss_now);
			}
			TCP_SKB_CB(skb)->seq += copy;
		}

		len += copy;

		if (len >= probe_size)
			break;
	}
	tcp_init_tso_segs(sk, nskb, nskb->len);

	/* We're ready to send.  If this fails, the probe will
	 * be resegmented into mss-sized pieces by tcp_write_xmit().
	 */
	if (!tcp_transmit_skb(sk, nskb, 1, GFP_ATOMIC)) {
		/* Decrement cwnd here because we are sending
		 * effectively two packets. */
		tp->snd_cwnd--;
		tcp_event_new_data_sent(sk, nskb);

		icsk->icsk_mtup.probe_size = tcp_mss_to_mtu(sk, nskb->len);
		tp->mtu_probe.probe_seq_start = TCP_SKB_CB(nskb)->seq;
		tp->mtu_probe.probe_seq_end = TCP_SKB_CB(nskb)->end_seq;

		return 1;
	}

	return -1;
}

/* This routine writes packets to the network.  It advances the
 * send_head.  This happens as incoming acks open up the remote
 * window for us.
 *
 * LARGESEND note: !tcp_urg_mode is overkill, only frames between
 * snd_up-64k-mss .. snd_up cannot be large. However, taking into
 * account rare use of URG, this is not a big flaw.
 *
 * Send at most one packet when push_one > 0. Temporarily ignore
 * cwnd limit to force at most one packet out when push_one == 2.

 * Returns true, if no segments are in flight and we have queued segments,
 * but cannot send anything now because of SWS or another problem.
 */
static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
			   int push_one, gfp_t gfp)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *skb;
	unsigned int tso_segs, sent_pkts;
	int cwnd_quota;
	int result;
	bool is_cwnd_limited = false;

	sent_pkts = 0;

	if (!push_one) {
		/* Do MTU probing. */
		result = tcp_mtu_probe(sk);
		if (!result) {
			return false;
		} else if (result > 0) {
			sent_pkts = 1;
		}
	}

	while ((skb = tcp_send_head(sk))) {
		unsigned int limit;

		tso_segs = tcp_init_tso_segs(sk, skb, mss_now);
		BUG_ON(!tso_segs);

		if (unlikely(tp->repair) && tp->repair_queue == TCP_SEND_QUEUE) {
			/* "skb_mstamp" is used as a start point for the retransmit timer */
			skb_mstamp_get(&skb->skb_mstamp);
			goto repair; /* Skip network transmission */
		}

		cwnd_quota = tcp_cwnd_test(tp, skb);
		if (!cwnd_quota) {
			is_cwnd_limited = true;
			if (push_one == 2)
				/* Force out a loss probe pkt. */
				cwnd_quota = 1;
			else
				break;
		}

		if (unlikely(!tcp_snd_wnd_test(tp, skb, mss_now)))
			break;

		if (tso_segs == 1) {
			if (unlikely(!tcp_nagle_test(tp, skb, mss_now,
						     (tcp_skb_is_last(sk, skb) ?
						      nonagle : TCP_NAGLE_PUSH))))
				break;
		} else {
			if (!push_one &&
			    tcp_tso_should_defer(sk, skb, &is_cwnd_limited))
				break;
		}

		/* TCP Small Queues :
		 * Control number of packets in qdisc/devices to two packets / or ~1 ms.
		 * This allows for :
		 *  - better RTT estimation and ACK scheduling
		 *  - faster recovery
		 *  - high rates
		 * Alas, some drivers / subsystems require a fair amount
		 * of queued bytes to ensure line rate.
		 * One example is wifi aggregation (802.11 AMPDU)
		 */
		limit = max_t(unsigned int, sysctl_tcp_limit_output_bytes,
			      sk->sk_pacing_rate >> 10);

		if (atomic_read(&sk->sk_wmem_alloc) > limit) {
			set_bit(TSQ_THROTTLED, &tp->tsq_flags);
			/* It is possible TX completion already happened
			 * before we set TSQ_THROTTLED, so we must
			 * test again the condition.
			 */
			smp_mb__after_atomic();
			if (atomic_read(&sk->sk_wmem_alloc) > limit)
				break;
		}

		limit = mss_now;
		if (tso_segs > 1 && !tcp_urg_mode(tp))
			limit = tcp_mss_split_point(sk, skb, mss_now,
						    min_t(unsigned int,
							  cwnd_quota,
							  sk->sk_gso_max_segs),
						    nonagle);

		if (skb->len > limit &&
		    unlikely(tso_fragment(sk, skb, limit, mss_now, gfp)))
			break;

		if (unlikely(tcp_transmit_skb(sk, skb, 1, gfp)))
			break;

repair:
		/* Advance the send_head.  This one is sent out.
		 * This call will increment packets_out.
		 */
		tcp_event_new_data_sent(sk, skb);

		tcp_minshall_update(tp, mss_now, skb);
		sent_pkts += tcp_skb_pcount(skb);

		if (push_one)
			break;
	}

	if (likely(sent_pkts)) {
		if (tcp_in_cwnd_reduction(sk))
			tp->prr_out += sent_pkts;

		/* Send one loss probe per tail loss episode. */
		if (push_one != 2)
			tcp_schedule_loss_probe(sk);
		tcp_cwnd_validate(sk, is_cwnd_limited);
		return false;
	}
	return (push_one == 2) || (!tp->packets_out && tcp_send_head(sk));
}

bool tcp_schedule_loss_probe(struct sock *sk)
{
	struct inet_connection_sock *icsk = inet_csk(sk);
	struct tcp_sock *tp = tcp_sk(sk);
	u32 timeout, tlp_time_stamp, rto_time_stamp;
	u32 rtt = usecs_to_jiffies(tp->srtt_us >> 3);

	if (WARN_ON(icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS))
		return false;
	/* No consecutive loss probes. */
	if (WARN_ON(icsk->icsk_pending == ICSK_TIME_LOSS_PROBE)) {
		tcp_rearm_rto(sk);
		return false;
	}
	/* Don't do any loss probe on a Fast Open connection before 3WHS
	 * finishes.
	 */
	if (sk->sk_state == TCP_SYN_RECV)
		return false;

	/* TLP is only scheduled when next timer event is RTO. */
	if (icsk->icsk_pending != ICSK_TIME_RETRANS)
		return false;

	/* Schedule a loss probe in 2*RTT for SACK capable connections
	 * in Open state, that are either limited by cwnd or application.
	 */
	if (sysctl_tcp_early_retrans < 3 || !tp->srtt_us || !tp->packets_out ||
	    !tcp_is_sack(tp) || inet_csk(sk)->icsk_ca_state != TCP_CA_Open)
		return false;

	if ((tp->snd_cwnd > tcp_packets_in_flight(tp)) &&
	     tcp_send_head(sk))
		return false;

	/* Probe timeout is at least 1.5*rtt + TCP_DELACK_MAX to account
	 * for delayed ack when there's one outstanding packet.
	 */
	timeout = rtt << 1;
	if (tp->packets_out == 1)
		timeout = max_t(u32, timeout,
				(rtt + (rtt >> 1) + TCP_DELACK_MAX));
	timeout = max_t(u32, timeout, msecs_to_jiffies(10));

	/* If RTO is shorter, just schedule TLP in its place. */
	tlp_time_stamp = tcp_time_stamp + timeout;
	rto_time_stamp = (u32)inet_csk(sk)->icsk_timeout;
	if ((s32)(tlp_time_stamp - rto_time_stamp) > 0) {
		s32 delta = rto_time_stamp - tcp_time_stamp;
		if (delta > 0)
			timeout = delta;
	}

	inet_csk_reset_xmit_timer(sk, ICSK_TIME_LOSS_PROBE, timeout,
				  TCP_RTO_MAX);
	return true;
}

/* Thanks to skb fast clones, we can detect if a prior transmit of
 * a packet is still in a qdisc or driver queue.
 * In this case, there is very little point doing a retransmit !
 * Note: This is called from BH context only.
 */
static bool skb_still_in_host_queue(const struct sock *sk,
				    const struct sk_buff *skb)
{
	if (unlikely(skb_fclone_busy(skb))) {
		NET_INC_STATS_BH(sock_net(sk),
				 LINUX_MIB_TCPSPURIOUS_RTX_HOSTQUEUES);
		return true;
	}
	return false;
}

/* When probe timeout (PTO) fires, send a new segment if one exists, else
 * retransmit the last segment.
 */
void tcp_send_loss_probe(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *skb;
	int pcount;
	int mss = tcp_current_mss(sk);
	int err = -1;

	if (tcp_send_head(sk) != NULL) {
		err = tcp_write_xmit(sk, mss, TCP_NAGLE_OFF, 2, GFP_ATOMIC);
		goto rearm_timer;
	}

	/* At most one outstanding TLP retransmission. */
	if (tp->tlp_high_seq)
		goto rearm_timer;

	/* Retransmit last segment. */
	skb = tcp_write_queue_tail(sk);
	if (WARN_ON(!skb))
		goto rearm_timer;

	if (skb_still_in_host_queue(sk, skb))
		goto rearm_timer;

	pcount = tcp_skb_pcount(skb);
	if (WARN_ON(!pcount))
		goto rearm_timer;

	if ((pcount > 1) && (skb->len > (pcount - 1) * mss)) {
		if (unlikely(tcp_fragment(sk, skb, (pcount - 1) * mss, mss,
					  GFP_ATOMIC)))
			goto rearm_timer;
		skb = tcp_write_queue_tail(sk);
	}

	if (WARN_ON(!skb || !tcp_skb_pcount(skb)))
		goto rearm_timer;

	err = __tcp_retransmit_skb(sk, skb);

	/* Record snd_nxt for loss detection. */
	if (likely(!err))
		tp->tlp_high_seq = tp->snd_nxt;

rearm_timer:
	inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
				  inet_csk(sk)->icsk_rto,
				  TCP_RTO_MAX);

	if (likely(!err))
		NET_INC_STATS_BH(sock_net(sk),
				 LINUX_MIB_TCPLOSSPROBES);
}

/* Push out any pending frames which were held back due to
 * TCP_CORK or attempt at coalescing tiny packets.
 * The socket must be locked by the caller.
 */
void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss,
			       int nonagle)
{
	/* If we are closed, the bytes will have to remain here.
	 * In time closedown will finish, we empty the write queue and
	 * all will be happy.
	 */
	if (unlikely(sk->sk_state == TCP_CLOSE))
		return;

	if (tcp_write_xmit(sk, cur_mss, nonagle, 0,
			   sk_gfp_atomic(sk, GFP_ATOMIC)))
		tcp_check_probe_timer(sk);
}

/* Send _single_ skb sitting at the send head. This function requires
 * true push pending frames to setup probe timer etc.
 */
void tcp_push_one(struct sock *sk, unsigned int mss_now)
{
	struct sk_buff *skb = tcp_send_head(sk);

	BUG_ON(!skb || skb->len < mss_now);

	tcp_write_xmit(sk, mss_now, TCP_NAGLE_PUSH, 1, sk->sk_allocation);
}

/* This function returns the amount that we can raise the
 * usable window based on the following constraints
 *
 * 1. The window can never be shrunk once it is offered (RFC 793)
 * 2. We limit memory per socket
 *
 * RFC 1122:
 * "the suggested [SWS] avoidance algorithm for the receiver is to keep
 *  RECV.NEXT + RCV.WIN fixed until:
 *  RCV.BUFF - RCV.USER - RCV.WINDOW >= min(1/2 RCV.BUFF, MSS)"
 *
 * i.e. don't raise the right edge of the window until you can raise
 * it at least MSS bytes.
 *
 * Unfortunately, the recommended algorithm breaks header prediction,
 * since header prediction assumes th->window stays fixed.
 *
 * Strictly speaking, keeping th->window fixed violates the receiver
 * side SWS prevention criteria. The problem is that under this rule
 * a stream of single byte packets will cause the right side of the
 * window to always advance by a single byte.
 *
 * Of course, if the sender implements sender side SWS prevention
 * then this will not be a problem.
 *
 * BSD seems to make the following compromise:
 *
 *	If the free space is less than the 1/4 of the maximum
 *	space available and the free space is less than 1/2 mss,
 *	then set the window to 0.
 *	[ Actually, bsd uses MSS and 1/4 of maximal _window_ ]
 *	Otherwise, just prevent the window from shrinking
 *	and from being larger than the largest representable value.
 *
 * This prevents incremental opening of the window in the regime
 * where TCP is limited by the speed of the reader side taking
 * data out of the TCP receive queue. It does nothing about
 * those cases where the window is constrained on the sender side
 * because the pipeline is full.
 *
 * BSD also seems to "accidentally" limit itself to windows that are a
 * multiple of MSS, at least until the free space gets quite small.
 * This would appear to be a side effect of the mbuf implementation.
 * Combining these two algorithms results in the observed behavior
 * of having a fixed window size at almost all times.
 *
 * Below we obtain similar behavior by forcing the offered window to
 * a multiple of the mss when it is feasible to do so.
 *
 * Note, we don't "adjust" for TIMESTAMP or SACK option bytes.
 * Regular options like TIMESTAMP are taken into account.
 */
u32 __tcp_select_window(struct sock *sk)
{
	struct inet_connection_sock *icsk = inet_csk(sk);
	struct tcp_sock *tp = tcp_sk(sk);
	/* MSS for the peer's data.  Previous versions used mss_clamp
	 * here.  I don't know if the value based on our guesses
	 * of peer's MSS is better for the performance.  It's more correct
	 * but may be worse for the performance because of rcv_mss
	 * fluctuations.  --SAW  1998/11/1
	 */
	int mss = icsk->icsk_ack.rcv_mss;
	int free_space = tcp_space(sk);
	int allowed_space = tcp_full_space(sk);
	int full_space = min_t(int, tp->window_clamp, allowed_space);
	int window;

	if (mss > full_space)
		mss = full_space;

	if (free_space < (full_space >> 1)) {
		icsk->icsk_ack.quick = 0;

		if (sk_under_memory_pressure(sk))
			tp->rcv_ssthresh = min(tp->rcv_ssthresh,
					       4U * tp->advmss);

		/* free_space might become our new window, make sure we don't
		 * increase it due to wscale.
		 */
		free_space = round_down(free_space, 1 << tp->rx_opt.rcv_wscale);

		/* if free space is less than mss estimate, or is below 1/16th
		 * of the maximum allowed, try to move to zero-window, else
		 * tcp_clamp_window() will grow rcv buf up to tcp_rmem[2], and
		 * new incoming data is dropped due to memory limits.
		 * With large window, mss test triggers way too late in order
		 * to announce zero window in time before rmem limit kicks in.
		 */
		if (free_space < (allowed_space >> 4) || free_space < mss)
			return 0;
	}

	if (free_space > tp->rcv_ssthresh)
		free_space = tp->rcv_ssthresh;

	/* Don't do rounding if we are using window scaling, since the
	 * scaled window will not line up with the MSS boundary anyway.
	 */
	window = tp->rcv_wnd;
	if (tp->rx_opt.rcv_wscale) {
		window = free_space;

		/* Advertise enough space so that it won't get scaled away.
		 * Import case: prevent zero window announcement if
		 * 1<<rcv_wscale > mss.
		 */
		if (((window >> tp->rx_opt.rcv_wscale) << tp->rx_opt.rcv_wscale) != window)
			window = (((window >> tp->rx_opt.rcv_wscale) + 1)
				  << tp->rx_opt.rcv_wscale);
	} else {
		/* Get the largest window that is a nice multiple of mss.
		 * Window clamp already applied above.
		 * If our current window offering is within 1 mss of the
		 * free space we just keep it. This prevents the divide
		 * and multiply from happening most of the time.
		 * We also don't do any window rounding when the free space
		 * is too small.
		 */
		if (window <= free_space - mss || window > free_space)
			window = (free_space / mss) * mss;
		else if (mss == full_space &&
			 free_space > window + (full_space >> 1))
			window = free_space;
	}

	return window;
}

/* Collapses two adjacent SKB's during retransmission. */
static void tcp_collapse_retrans(struct sock *sk, struct sk_buff *skb)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *next_skb = tcp_write_queue_next(sk, skb);
	int skb_size, next_skb_size;

	skb_size = skb->len;
	next_skb_size = next_skb->len;

	BUG_ON(tcp_skb_pcount(skb) != 1 || tcp_skb_pcount(next_skb) != 1);

	tcp_highest_sack_combine(sk, next_skb, skb);

	tcp_unlink_write_queue(next_skb, sk);

	skb_copy_from_linear_data(next_skb, skb_put(skb, next_skb_size),
				  next_skb_size);

	if (next_skb->ip_summed == CHECKSUM_PARTIAL)
		skb->ip_summed = CHECKSUM_PARTIAL;

	if (skb->ip_summed != CHECKSUM_PARTIAL)
		skb->csum = csum_block_add(skb->csum, next_skb->csum, skb_size);

	/* Update sequence range on original skb. */
	TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(next_skb)->end_seq;

	/* Merge over control information. This moves PSH/FIN etc. over */
	TCP_SKB_CB(skb)->tcp_flags |= TCP_SKB_CB(next_skb)->tcp_flags;

	/* All done, get rid of second SKB and account for it so
	 * packet counting does not break.
	 */
	TCP_SKB_CB(skb)->sacked |= TCP_SKB_CB(next_skb)->sacked & TCPCB_EVER_RETRANS;

	/* changed transmit queue under us so clear hints */
	tcp_clear_retrans_hints_partial(tp);
	if (next_skb == tp->retransmit_skb_hint)
		tp->retransmit_skb_hint = skb;

	tcp_adjust_pcount(sk, next_skb, tcp_skb_pcount(next_skb));

	sk_wmem_free_skb(sk, next_skb);
}

/* Check if coalescing SKBs is legal. */
static bool tcp_can_collapse(const struct sock *sk, const struct sk_buff *skb)
{
	if (tcp_skb_pcount(skb) > 1)
		return false;
	/* TODO: SACK collapsing could be used to remove this condition */
	if (skb_shinfo(skb)->nr_frags != 0)
		return false;
	if (skb_cloned(skb))
		return false;
	if (skb == tcp_send_head(sk))
		return false;
	/* Some heurestics for collapsing over SACK'd could be invented */
	if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
		return false;

	return true;
}

/* Collapse packets in the retransmit queue to make to create
 * less packets on the wire. This is only done on retransmission.
 */
static void tcp_retrans_try_collapse(struct sock *sk, struct sk_buff *to,
				     int space)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *skb = to, *tmp;
	bool first = true;

	if (!sysctl_tcp_retrans_collapse)
		return;
	if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)
		return;

	tcp_for_write_queue_from_safe(skb, tmp, sk) {
		if (!tcp_can_collapse(sk, skb))
			break;

		space -= skb->len;

		if (first) {
			first = false;
			continue;
		}

		if (space < 0)
			break;
		/* Punt if not enough space exists in the first SKB for
		 * the data in the second
		 */
		if (skb->len > skb_availroom(to))
			break;

		if (after(TCP_SKB_CB(skb)->end_seq, tcp_wnd_end(tp)))
			break;

		tcp_collapse_retrans(sk, to);
	}
}

/* This retransmits one SKB.  Policy decisions and retransmit queue
 * state updates are done by the caller.  Returns non-zero if an
 * error occurred which prevented the send.
 */
int __tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct inet_connection_sock *icsk = inet_csk(sk);
	unsigned int cur_mss;
	int err;

	/* Inconslusive MTU probe */
	if (icsk->icsk_mtup.probe_size) {
		icsk->icsk_mtup.probe_size = 0;
	}

	/* Do not sent more than we queued. 1/4 is reserved for possible
	 * copying overhead: fragmentation, tunneling, mangling etc.
	 */
	if (atomic_read(&sk->sk_wmem_alloc) >
	    min(sk->sk_wmem_queued + (sk->sk_wmem_queued >> 2), sk->sk_sndbuf))
		return -EAGAIN;

	if (skb_still_in_host_queue(sk, skb))
		return -EBUSY;

	if (before(TCP_SKB_CB(skb)->seq, tp->snd_una)) {
		if (before(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
			BUG();
		if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
			return -ENOMEM;
	}

	if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk))
		return -EHOSTUNREACH; /* Routing failure or similar. */

	cur_mss = tcp_current_mss(sk);

	/* If receiver has shrunk his window, and skb is out of
	 * new window, do not retransmit it. The exception is the
	 * case, when window is shrunk to zero. In this case
	 * our retransmit serves as a zero window probe.
	 */
	if (!before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp)) &&
	    TCP_SKB_CB(skb)->seq != tp->snd_una)
		return -EAGAIN;

	if (skb->len > cur_mss) {
		if (tcp_fragment(sk, skb, cur_mss, cur_mss, GFP_ATOMIC))
			return -ENOMEM; /* We'll try again later. */
	} else {
		int oldpcount = tcp_skb_pcount(skb);

		if (unlikely(oldpcount > 1)) {
			if (skb_unclone(skb, GFP_ATOMIC))
				return -ENOMEM;
			tcp_init_tso_segs(sk, skb, cur_mss);
			tcp_adjust_pcount(sk, skb, oldpcount - tcp_skb_pcount(skb));
		}
	}

	tcp_retrans_try_collapse(sk, skb, cur_mss);

	/* Make a copy, if the first transmission SKB clone we made
	 * is still in somebody's hands, else make a clone.
	 */

	/* make sure skb->data is aligned on arches that require it
	 * and check if ack-trimming & collapsing extended the headroom
	 * beyond what csum_start can cover.
	 */
	if (unlikely((NET_IP_ALIGN && ((unsigned long)skb->data & 3)) ||
		     skb_headroom(skb) >= 0xFFFF)) {
		struct sk_buff *nskb = __pskb_copy(skb, MAX_TCP_HEADER,
						   GFP_ATOMIC);
		err = nskb ? tcp_transmit_skb(sk, nskb, 0, GFP_ATOMIC) :
			     -ENOBUFS;
	} else {
		err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
	}

	if (likely(!err)) {
		TCP_SKB_CB(skb)->sacked |= TCPCB_EVER_RETRANS;
		/* Update global TCP statistics. */
		TCP_INC_STATS(sock_net(sk), TCP_MIB_RETRANSSEGS);
		if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)
			NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSYNRETRANS);
		tp->total_retrans++;
	}
	return err;
}

int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb)
{
	struct tcp_sock *tp = tcp_sk(sk);
	int err = __tcp_retransmit_skb(sk, skb);

	if (err == 0) {
#if FASTRETRANS_DEBUG > 0
		if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
			net_dbg_ratelimited("retrans_out leaked\n");
		}
#endif
		if (!tp->retrans_out)
			tp->lost_retrans_low = tp->snd_nxt;
		TCP_SKB_CB(skb)->sacked |= TCPCB_RETRANS;
		tp->retrans_out += tcp_skb_pcount(skb);

		/* Save stamp of the first retransmit. */
		if (!tp->retrans_stamp)
			tp->retrans_stamp = tcp_skb_timestamp(skb);

		/* snd_nxt is stored to detect loss of retransmitted segment,
		 * see tcp_input.c tcp_sacktag_write_queue().
		 */
		TCP_SKB_CB(skb)->ack_seq = tp->snd_nxt;
	} else if (err != -EBUSY) {
		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPRETRANSFAIL);
	}

	if (tp->undo_retrans < 0)
		tp->undo_retrans = 0;
	tp->undo_retrans += tcp_skb_pcount(skb);
	return err;
}

/* Check if we forward retransmits are possible in the current
 * window/congestion state.
 */
static bool tcp_can_forward_retransmit(struct sock *sk)
{
	const struct inet_connection_sock *icsk = inet_csk(sk);
	const struct tcp_sock *tp = tcp_sk(sk);

	/* Forward retransmissions are possible only during Recovery. */
	if (icsk->icsk_ca_state != TCP_CA_Recovery)
		return false;

	/* No forward retransmissions in Reno are possible. */
	if (tcp_is_reno(tp))
		return false;

	/* Yeah, we have to make difficult choice between forward transmission
	 * and retransmission... Both ways have their merits...
	 *
	 * For now we do not retransmit anything, while we have some new
	 * segments to send. In the other cases, follow rule 3 for
	 * NextSeg() specified in RFC3517.
	 */

	if (tcp_may_send_now(sk))
		return false;

	return true;
}

/* This gets called after a retransmit timeout, and the initially
 * retransmitted data is acknowledged.  It tries to continue
 * resending the rest of the retransmit queue, until either
 * we've sent it all or the congestion window limit is reached.
 * If doing SACK, the first ACK which comes back for a timeout
 * based retransmit packet might feed us FACK information again.
 * If so, we use it to avoid unnecessarily retransmissions.
 */
void tcp_xmit_retransmit_queue(struct sock *sk)
{
	const struct inet_connection_sock *icsk = inet_csk(sk);
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *skb;
	struct sk_buff *hole = NULL;
	u32 last_lost;
	int mib_idx;
	int fwd_rexmitting = 0;

	if (!tp->packets_out)
		return;

	if (!tp->lost_out)
		tp->retransmit_high = tp->snd_una;

	if (tp->retransmit_skb_hint) {
		skb = tp->retransmit_skb_hint;
		last_lost = TCP_SKB_CB(skb)->end_seq;
		if (after(last_lost, tp->retransmit_high))
			last_lost = tp->retransmit_high;
	} else {
		skb = tcp_write_queue_head(sk);
		last_lost = tp->snd_una;
	}

	tcp_for_write_queue_from(skb, sk) {
		__u8 sacked = TCP_SKB_CB(skb)->sacked;

		if (skb == tcp_send_head(sk))
			break;
		/* we could do better than to assign each time */
		if (hole == NULL)
			tp->retransmit_skb_hint = skb;

		/* Assume this retransmit will generate
		 * only one packet for congestion window
		 * calculation purposes.  This works because
		 * tcp_retransmit_skb() will chop up the
		 * packet to be MSS sized and all the
		 * packet counting works out.
		 */
		if (tcp_packets_in_flight(tp) >= tp->snd_cwnd)
			return;

		if (fwd_rexmitting) {
begin_fwd:
			if (!before(TCP_SKB_CB(skb)->seq, tcp_highest_sack_seq(tp)))
				break;
			mib_idx = LINUX_MIB_TCPFORWARDRETRANS;

		} else if (!before(TCP_SKB_CB(skb)->seq, tp->retransmit_high)) {
			tp->retransmit_high = last_lost;
			if (!tcp_can_forward_retransmit(sk))
				break;
			/* Backtrack if necessary to non-L'ed skb */
			if (hole != NULL) {
				skb = hole;
				hole = NULL;
			}
			fwd_rexmitting = 1;
			goto begin_fwd;

		} else if (!(sacked & TCPCB_LOST)) {
			if (hole == NULL && !(sacked & (TCPCB_SACKED_RETRANS|TCPCB_SACKED_ACKED)))
				hole = skb;
			continue;

		} else {
			last_lost = TCP_SKB_CB(skb)->end_seq;
			if (icsk->icsk_ca_state != TCP_CA_Loss)
				mib_idx = LINUX_MIB_TCPFASTRETRANS;
			else
				mib_idx = LINUX_MIB_TCPSLOWSTARTRETRANS;
		}

		if (sacked & (TCPCB_SACKED_ACKED|TCPCB_SACKED_RETRANS))
			continue;

		if (tcp_retransmit_skb(sk, skb))
			return;

		NET_INC_STATS_BH(sock_net(sk), mib_idx);

		if (tcp_in_cwnd_reduction(sk))
			tp->prr_out += tcp_skb_pcount(skb);

		if (skb == tcp_write_queue_head(sk))
			inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
						  inet_csk(sk)->icsk_rto,
						  TCP_RTO_MAX);
	}
}

/* Send a fin.  The caller locks the socket for us.  This cannot be
 * allowed to fail queueing a FIN frame under any circumstances.
 */
void tcp_send_fin(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *skb = tcp_write_queue_tail(sk);
	int mss_now;

	/* Optimization, tack on the FIN if we have a queue of
	 * unsent frames.  But be careful about outgoing SACKS
	 * and IP options.
	 */
	mss_now = tcp_current_mss(sk);

	if (tcp_send_head(sk) != NULL) {
		TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_FIN;
		TCP_SKB_CB(skb)->end_seq++;
		tp->write_seq++;
	} else {
		/* Socket is locked, keep trying until memory is available. */
		for (;;) {
			skb = alloc_skb_fclone(MAX_TCP_HEADER,
					       sk->sk_allocation);
			if (skb)
				break;
			yield();
		}

		/* Reserve space for headers and prepare control bits. */
		skb_reserve(skb, MAX_TCP_HEADER);
		/* FIN eats a sequence byte, write_seq advanced by tcp_queue_skb(). */
		tcp_init_nondata_skb(skb, tp->write_seq,
				     TCPHDR_ACK | TCPHDR_FIN);
		tcp_queue_skb(sk, skb);
	}
	__tcp_push_pending_frames(sk, mss_now, TCP_NAGLE_OFF);
}

/* We get here when a process closes a file descriptor (either due to
 * an explicit close() or as a byproduct of exit()'ing) and there
 * was unread data in the receive queue.  This behavior is recommended
 * by RFC 2525, section 2.17.  -DaveM
 */
void tcp_send_active_reset(struct sock *sk, gfp_t priority)
{
	struct sk_buff *skb;

	/* NOTE: No TCP options attached and we never retransmit this. */
	skb = alloc_skb(MAX_TCP_HEADER, priority);
	if (!skb) {
		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
		return;
	}

	/* Reserve space for headers and prepare control bits. */
	skb_reserve(skb, MAX_TCP_HEADER);
	tcp_init_nondata_skb(skb, tcp_acceptable_seq(sk),
			     TCPHDR_ACK | TCPHDR_RST);
	/* Send it off. */
	if (tcp_transmit_skb(sk, skb, 0, priority))
		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);

	TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTRSTS);
}

/* Send a crossed SYN-ACK during socket establishment.
 * WARNING: This routine must only be called when we have already sent
 * a SYN packet that crossed the incoming SYN that caused this routine
 * to get called. If this assumption fails then the initial rcv_wnd
 * and rcv_wscale values will not be correct.
 */
int tcp_send_synack(struct sock *sk)
{
	struct sk_buff *skb;

	skb = tcp_write_queue_head(sk);
	if (skb == NULL || !(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)) {
		pr_debug("%s: wrong queue state\n", __func__);
		return -EFAULT;
	}
	if (!(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_ACK)) {
		if (skb_cloned(skb)) {
			struct sk_buff *nskb = skb_copy(skb, GFP_ATOMIC);
			if (nskb == NULL)
				return -ENOMEM;
			tcp_unlink_write_queue(skb, sk);
			__skb_header_release(nskb);
			__tcp_add_write_queue_head(sk, nskb);
			sk_wmem_free_skb(sk, skb);
			sk->sk_wmem_queued += nskb->truesize;
			sk_mem_charge(sk, nskb->truesize);
			skb = nskb;
		}

		TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ACK;
		tcp_ecn_send_synack(sk, skb);
	}
	return tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
}

/**
 * tcp_make_synack - Prepare a SYN-ACK.
 * sk: listener socket
 * dst: dst entry attached to the SYNACK
 * req: request_sock pointer
 *
 * Allocate one skb and build a SYNACK packet.
 * @dst is consumed : Caller should not use it again.
 */
struct sk_buff *tcp_make_synack(struct sock *sk, struct dst_entry *dst,
				struct request_sock *req,
				struct tcp_fastopen_cookie *foc)
{
	struct tcp_out_options opts;
	struct inet_request_sock *ireq = inet_rsk(req);
	struct tcp_sock *tp = tcp_sk(sk);
	struct tcphdr *th;
	struct sk_buff *skb;
	struct tcp_md5sig_key *md5;
	int tcp_header_size;
	int mss;

	skb = sock_wmalloc(sk, MAX_TCP_HEADER, 1, GFP_ATOMIC);
	if (unlikely(!skb)) {
		dst_release(dst);
		return NULL;
	}
	/* Reserve space for headers. */
	skb_reserve(skb, MAX_TCP_HEADER);

	skb_dst_set(skb, dst);
	security_skb_owned_by(skb, sk);

	mss = dst_metric_advmss(dst);
	if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < mss)
		mss = tp->rx_opt.user_mss;

	memset(&opts, 0, sizeof(opts));
#ifdef CONFIG_SYN_COOKIES
	if (unlikely(req->cookie_ts))
		skb->skb_mstamp.stamp_jiffies = cookie_init_timestamp(req);
	else
#endif
	skb_mstamp_get(&skb->skb_mstamp);
	tcp_header_size = tcp_synack_options(sk, req, mss, skb, &opts, &md5,
					     foc) + sizeof(*th);

	skb_push(skb, tcp_header_size);
	skb_reset_transport_header(skb);

	th = tcp_hdr(skb);
	memset(th, 0, sizeof(struct tcphdr));
	th->syn = 1;
	th->ack = 1;
	tcp_ecn_make_synack(req, th, sk);
	th->source = htons(ireq->ir_num);
	th->dest = ireq->ir_rmt_port;
	/* Setting of flags are superfluous here for callers (and ECE is
	 * not even correctly set)
	 */
	tcp_init_nondata_skb(skb, tcp_rsk(req)->snt_isn,
			     TCPHDR_SYN | TCPHDR_ACK);

	th->seq = htonl(TCP_SKB_CB(skb)->seq);
	/* XXX data is queued and acked as is. No buffer/window check */
	th->ack_seq = htonl(tcp_rsk(req)->rcv_nxt);

	/* RFC1323: The window in SYN & SYN/ACK segments is never scaled. */
	th->window = htons(min(req->rcv_wnd, 65535U));
	tcp_options_write((__be32 *)(th + 1), tp, &opts);
	th->doff = (tcp_header_size >> 2);
	TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_OUTSEGS);

#ifdef CONFIG_TCP_MD5SIG
	/* Okay, we have all we need - do the md5 hash if needed */
	if (md5) {
		tcp_rsk(req)->af_specific->calc_md5_hash(opts.hash_location,
					       md5, NULL, req, skb);
	}
#endif

	return skb;
}
EXPORT_SYMBOL(tcp_make_synack);

/* Do all connect socket setups that can be done AF independent. */
static void tcp_connect_init(struct sock *sk)
{
	const struct dst_entry *dst = __sk_dst_get(sk);
	struct tcp_sock *tp = tcp_sk(sk);
	__u8 rcv_wscale;

	/* We'll fix this up when we get a response from the other end.
	 * See tcp_input.c:tcp_rcv_state_process case TCP_SYN_SENT.
	 */
	tp->tcp_header_len = sizeof(struct tcphdr) +
		(sysctl_tcp_timestamps ? TCPOLEN_TSTAMP_ALIGNED : 0);

#ifdef CONFIG_TCP_MD5SIG
	if (tp->af_specific->md5_lookup(sk, sk) != NULL)
		tp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED;
#endif

	/* If user gave his TCP_MAXSEG, record it to clamp */
	if (tp->rx_opt.user_mss)
		tp->rx_opt.mss_clamp = tp->rx_opt.user_mss;
	tp->max_window = 0;
	tcp_mtup_init(sk);
	tcp_sync_mss(sk, dst_mtu(dst));

	if (!tp->window_clamp)
		tp->window_clamp = dst_metric(dst, RTAX_WINDOW);
	tp->advmss = dst_metric_advmss(dst);
	if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < tp->advmss)
		tp->advmss = tp->rx_opt.user_mss;

	tcp_initialize_rcv_mss(sk);

	/* limit the window selection if the user enforce a smaller rx buffer */
	if (sk->sk_userlocks & SOCK_RCVBUF_LOCK &&
	    (tp->window_clamp > tcp_full_space(sk) || tp->window_clamp == 0))
		tp->window_clamp = tcp_full_space(sk);

	tcp_select_initial_window(tcp_full_space(sk),
				  tp->advmss - (tp->rx_opt.ts_recent_stamp ? tp->tcp_header_len - sizeof(struct tcphdr) : 0),
				  &tp->rcv_wnd,
				  &tp->window_clamp,
				  sysctl_tcp_window_scaling,
				  &rcv_wscale,
				  dst_metric(dst, RTAX_INITRWND));

	tp->rx_opt.rcv_wscale = rcv_wscale;
	tp->rcv_ssthresh = tp->rcv_wnd;

	sk->sk_err = 0;
	sock_reset_flag(sk, SOCK_DONE);
	tp->snd_wnd = 0;
	tcp_init_wl(tp, 0);
	tp->snd_una = tp->write_seq;
	tp->snd_sml = tp->write_seq;
	tp->snd_up = tp->write_seq;
	tp->snd_nxt = tp->write_seq;

	if (likely(!tp->repair))
		tp->rcv_nxt = 0;
	else
		tp->rcv_tstamp = tcp_time_stamp;
	tp->rcv_wup = tp->rcv_nxt;
	tp->copied_seq = tp->rcv_nxt;

	inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT;
	inet_csk(sk)->icsk_retransmits = 0;
	tcp_clear_retrans(tp);
}

static void tcp_connect_queue_skb(struct sock *sk, struct sk_buff *skb)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct tcp_skb_cb *tcb = TCP_SKB_CB(skb);

	tcb->end_seq += skb->len;
	__skb_header_release(skb);
	__tcp_add_write_queue_tail(sk, skb);
	sk->sk_wmem_queued += skb->truesize;
	sk_mem_charge(sk, skb->truesize);
	tp->write_seq = tcb->end_seq;
	tp->packets_out += tcp_skb_pcount(skb);
}

/* Build and send a SYN with data and (cached) Fast Open cookie. However,
 * queue a data-only packet after the regular SYN, such that regular SYNs
 * are retransmitted on timeouts. Also if the remote SYN-ACK acknowledges
 * only the SYN sequence, the data are retransmitted in the first ACK.
 * If cookie is not cached or other error occurs, falls back to send a
 * regular SYN with Fast Open cookie request option.
 */
static int tcp_send_syn_data(struct sock *sk, struct sk_buff *syn)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct tcp_fastopen_request *fo = tp->fastopen_req;
	int syn_loss = 0, space, i, err = 0, iovlen = fo->data->msg_iovlen;
	struct sk_buff *syn_data = NULL, *data;
	unsigned long last_syn_loss = 0;

	tp->rx_opt.mss_clamp = tp->advmss;  /* If MSS is not cached */
	tcp_fastopen_cache_get(sk, &tp->rx_opt.mss_clamp, &fo->cookie,
			       &syn_loss, &last_syn_loss);
	/* Recurring FO SYN losses: revert to regular handshake temporarily */
	if (syn_loss > 1 &&
	    time_before(jiffies, last_syn_loss + (60*HZ << syn_loss))) {
		fo->cookie.len = -1;
		goto fallback;
	}

	if (sysctl_tcp_fastopen & TFO_CLIENT_NO_COOKIE)
		fo->cookie.len = -1;
	else if (fo->cookie.len <= 0)
		goto fallback;

	/* MSS for SYN-data is based on cached MSS and bounded by PMTU and
	 * user-MSS. Reserve maximum option space for middleboxes that add
	 * private TCP options. The cost is reduced data space in SYN :(
	 */
	if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < tp->rx_opt.mss_clamp)
		tp->rx_opt.mss_clamp = tp->rx_opt.user_mss;
	space = __tcp_mtu_to_mss(sk, inet_csk(sk)->icsk_pmtu_cookie) -
		MAX_TCP_OPTION_SPACE;

	space = min_t(size_t, space, fo->size);

	/* limit to order-0 allocations */
	space = min_t(size_t, space, SKB_MAX_HEAD(MAX_TCP_HEADER));

	syn_data = skb_copy_expand(syn, MAX_TCP_HEADER, space,
				   sk->sk_allocation);
	if (syn_data == NULL)
		goto fallback;

	for (i = 0; i < iovlen && syn_data->len < space; ++i) {
		struct iovec *iov = &fo->data->msg_iov[i];
		unsigned char __user *from = iov->iov_base;
		int len = iov->iov_len;

		if (syn_data->len + len > space)
			len = space - syn_data->len;
		else if (i + 1 == iovlen)
			/* No more data pending in inet_wait_for_connect() */
			fo->data = NULL;

		if (skb_add_data(syn_data, from, len))
			goto fallback;
	}

	/* Queue a data-only packet after the regular SYN for retransmission */
	data = pskb_copy(syn_data, sk->sk_allocation);
	if (data == NULL)
		goto fallback;
	TCP_SKB_CB(data)->seq++;
	TCP_SKB_CB(data)->tcp_flags &= ~TCPHDR_SYN;
	TCP_SKB_CB(data)->tcp_flags = (TCPHDR_ACK|TCPHDR_PSH);
	tcp_connect_queue_skb(sk, data);
	fo->copied = data->len;

	/* syn_data is about to be sent, we need to take current time stamps
	 * for the packets that are in write queue : SYN packet and DATA
	 */
	skb_mstamp_get(&syn->skb_mstamp);
	data->skb_mstamp = syn->skb_mstamp;

	if (tcp_transmit_skb(sk, syn_data, 0, sk->sk_allocation) == 0) {
		tp->syn_data = (fo->copied > 0);
		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPORIGDATASENT);
		goto done;
	}
	syn_data = NULL;

fallback:
	/* Send a regular SYN with Fast Open cookie request option */
	if (fo->cookie.len > 0)
		fo->cookie.len = 0;
	err = tcp_transmit_skb(sk, syn, 1, sk->sk_allocation);
	if (err)
		tp->syn_fastopen = 0;
	kfree_skb(syn_data);
done:
	fo->cookie.len = -1;  /* Exclude Fast Open option for SYN retries */
	return err;
}

/* Build a SYN and send it off. */
int tcp_connect(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *buff;
	int err;

	tcp_connect_init(sk);

	if (unlikely(tp->repair)) {
		tcp_finish_connect(sk, NULL);
		return 0;
	}

	buff = alloc_skb_fclone(MAX_TCP_HEADER + 15, sk->sk_allocation);
	if (unlikely(buff == NULL))
		return -ENOBUFS;

	/* Reserve space for headers. */
	skb_reserve(buff, MAX_TCP_HEADER);

	tcp_init_nondata_skb(buff, tp->write_seq++, TCPHDR_SYN);
	tp->retrans_stamp = tcp_time_stamp;
	tcp_connect_queue_skb(sk, buff);
	tcp_ecn_send_syn(sk, buff);

	/* Send off SYN; include data in Fast Open. */
	err = tp->fastopen_req ? tcp_send_syn_data(sk, buff) :
	      tcp_transmit_skb(sk, buff, 1, sk->sk_allocation);
	if (err == -ECONNREFUSED)
		return err;

	/* We change tp->snd_nxt after the tcp_transmit_skb() call
	 * in order to make this packet get counted in tcpOutSegs.
	 */
	tp->snd_nxt = tp->write_seq;
	tp->pushed_seq = tp->write_seq;
	TCP_INC_STATS(sock_net(sk), TCP_MIB_ACTIVEOPENS);

	/* Timer for repeating the SYN until an answer. */
	inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
				  inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
	return 0;
}
EXPORT_SYMBOL(tcp_connect);

/* Send out a delayed ack, the caller does the policy checking
 * to see if we should even be here.  See tcp_input.c:tcp_ack_snd_check()
 * for details.
 */
void tcp_send_delayed_ack(struct sock *sk)
{
	struct inet_connection_sock *icsk = inet_csk(sk);
	int ato = icsk->icsk_ack.ato;
	unsigned long timeout;

	tcp_ca_event(sk, CA_EVENT_DELAYED_ACK);

	if (ato > TCP_DELACK_MIN) {
		const struct tcp_sock *tp = tcp_sk(sk);
		int max_ato = HZ / 2;

		if (icsk->icsk_ack.pingpong ||
		    (icsk->icsk_ack.pending & ICSK_ACK_PUSHED))
			max_ato = TCP_DELACK_MAX;

		/* Slow path, intersegment interval is "high". */

		/* If some rtt estimate is known, use it to bound delayed ack.
		 * Do not use inet_csk(sk)->icsk_rto here, use results of rtt measurements
		 * directly.
		 */
		if (tp->srtt_us) {
			int rtt = max_t(int, usecs_to_jiffies(tp->srtt_us >> 3),
					TCP_DELACK_MIN);

			if (rtt < max_ato)
				max_ato = rtt;
		}

		ato = min(ato, max_ato);
	}

	/* Stay within the limit we were given */
	timeout = jiffies + ato;

	/* Use new timeout only if there wasn't a older one earlier. */
	if (icsk->icsk_ack.pending & ICSK_ACK_TIMER) {
		/* If delack timer was blocked or is about to expire,
		 * send ACK now.
		 */
		if (icsk->icsk_ack.blocked ||
		    time_before_eq(icsk->icsk_ack.timeout, jiffies + (ato >> 2))) {
			tcp_send_ack(sk);
			return;
		}

		if (!time_before(timeout, icsk->icsk_ack.timeout))
			timeout = icsk->icsk_ack.timeout;
	}
	icsk->icsk_ack.pending |= ICSK_ACK_SCHED | ICSK_ACK_TIMER;
	icsk->icsk_ack.timeout = timeout;
	sk_reset_timer(sk, &icsk->icsk_delack_timer, timeout);
}

/* This routine sends an ack and also updates the window. */
void tcp_send_ack(struct sock *sk)
{
	struct sk_buff *buff;

	/* If we have been reset, we may not send again. */
	if (sk->sk_state == TCP_CLOSE)
		return;

	tcp_ca_event(sk, CA_EVENT_NON_DELAYED_ACK);

	/* We are not putting this on the write queue, so
	 * tcp_transmit_skb() will set the ownership to this
	 * sock.
	 */
	buff = alloc_skb(MAX_TCP_HEADER, sk_gfp_atomic(sk, GFP_ATOMIC));
	if (buff == NULL) {
		inet_csk_schedule_ack(sk);
		inet_csk(sk)->icsk_ack.ato = TCP_ATO_MIN;
		inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
					  TCP_DELACK_MAX, TCP_RTO_MAX);
		return;
	}

	/* Reserve space for headers and prepare control bits. */
	skb_reserve(buff, MAX_TCP_HEADER);
	tcp_init_nondata_skb(buff, tcp_acceptable_seq(sk), TCPHDR_ACK);

	/* Send it off, this clears delayed acks for us. */
	skb_mstamp_get(&buff->skb_mstamp);
	tcp_transmit_skb(sk, buff, 0, sk_gfp_atomic(sk, GFP_ATOMIC));
}
EXPORT_SYMBOL_GPL(tcp_send_ack);

/* This routine sends a packet with an out of date sequence
 * number. It assumes the other end will try to ack it.
 *
 * Question: what should we make while urgent mode?
 * 4.4BSD forces sending single byte of data. We cannot send
 * out of window data, because we have SND.NXT==SND.MAX...
 *
 * Current solution: to send TWO zero-length segments in urgent mode:
 * one is with SEG.SEQ=SND.UNA to deliver urgent pointer, another is
 * out-of-date with SND.UNA-1 to probe window.
 */
static int tcp_xmit_probe_skb(struct sock *sk, int urgent)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *skb;

	/* We don't queue it, tcp_transmit_skb() sets ownership. */
	skb = alloc_skb(MAX_TCP_HEADER, sk_gfp_atomic(sk, GFP_ATOMIC));
	if (skb == NULL)
		return -1;

	/* Reserve space for headers and set control bits. */
	skb_reserve(skb, MAX_TCP_HEADER);
	/* Use a previous sequence.  This should cause the other
	 * end to send an ack.  Don't queue or clone SKB, just
	 * send it.
	 */
	tcp_init_nondata_skb(skb, tp->snd_una - !urgent, TCPHDR_ACK);
	skb_mstamp_get(&skb->skb_mstamp);
	return tcp_transmit_skb(sk, skb, 0, GFP_ATOMIC);
}

void tcp_send_window_probe(struct sock *sk)
{
	if (sk->sk_state == TCP_ESTABLISHED) {
		tcp_sk(sk)->snd_wl1 = tcp_sk(sk)->rcv_nxt - 1;
		tcp_xmit_probe_skb(sk, 0);
	}
}

/* Initiate keepalive or window probe from timer. */
int tcp_write_wakeup(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *skb;

	if (sk->sk_state == TCP_CLOSE)
		return -1;

	if ((skb = tcp_send_head(sk)) != NULL &&
	    before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp))) {
		int err;
		unsigned int mss = tcp_current_mss(sk);
		unsigned int seg_size = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;

		if (before(tp->pushed_seq, TCP_SKB_CB(skb)->end_seq))
			tp->pushed_seq = TCP_SKB_CB(skb)->end_seq;

		/* We are probing the opening of a window
		 * but the window size is != 0
		 * must have been a result SWS avoidance ( sender )
		 */
		if (seg_size < TCP_SKB_CB(skb)->end_seq - TCP_SKB_CB(skb)->seq ||
		    skb->len > mss) {
			seg_size = min(seg_size, mss);
			TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH;
			if (tcp_fragment(sk, skb, seg_size, mss, GFP_ATOMIC))
				return -1;
		} else if (!tcp_skb_pcount(skb))
			tcp_set_skb_tso_segs(sk, skb, mss);

		TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH;
		err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
		if (!err)
			tcp_event_new_data_sent(sk, skb);
		return err;
	} else {
		if (between(tp->snd_up, tp->snd_una + 1, tp->snd_una + 0xFFFF))
			tcp_xmit_probe_skb(sk, 1);
		return tcp_xmit_probe_skb(sk, 0);
	}
}

/* A window probe timeout has occurred.  If window is not closed send
 * a partial packet else a zero probe.
 */
void tcp_send_probe0(struct sock *sk)
{
	struct inet_connection_sock *icsk = inet_csk(sk);
	struct tcp_sock *tp = tcp_sk(sk);
	unsigned long probe_max;
	int err;

	err = tcp_write_wakeup(sk);

	if (tp->packets_out || !tcp_send_head(sk)) {
		/* Cancel probe timer, if it is not required. */
		icsk->icsk_probes_out = 0;
		icsk->icsk_backoff = 0;
		return;
	}

	if (err <= 0) {
		if (icsk->icsk_backoff < sysctl_tcp_retries2)
			icsk->icsk_backoff++;
		icsk->icsk_probes_out++;
		probe_max = TCP_RTO_MAX;
	} else {
		/* If packet was not sent due to local congestion,
		 * do not backoff and do not remember icsk_probes_out.
		 * Let local senders to fight for local resources.
		 *
		 * Use accumulated backoff yet.
		 */
		if (!icsk->icsk_probes_out)
			icsk->icsk_probes_out = 1;
		probe_max = TCP_RESOURCE_PROBE_INTERVAL;
	}
	inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
				  inet_csk_rto_backoff(icsk, probe_max),
				  TCP_RTO_MAX);
}

int tcp_rtx_synack(struct sock *sk, struct request_sock *req)
{
	const struct tcp_request_sock_ops *af_ops = tcp_rsk(req)->af_specific;
	struct flowi fl;
	int res;

	res = af_ops->send_synack(sk, NULL, &fl, req, 0, NULL);
	if (!res) {
		TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_RETRANSSEGS);
		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSYNRETRANS);
	}
	return res;
}
EXPORT_SYMBOL(tcp_rtx_synack);