[pxe] Allow cached DHCP settings to be fetched before registration

Register cached DHCP settings in a placeholder standalone settings
block, to allow settings to be fetched during early initialisation
code (before the startup code that registers them into the root
settings hierarchy).

Signed-off-by: Michael Brown <mcb30@ipxe.org>

3 files changed, 34 insertions, 1 deletions

diff --git a/src/core/cachedhcp.c b/src/core/cachedhcp.c
index 2fa9b0c73..105201a57 100644
--- a/src/core/cachedhcp.c
+++ b/src/core/cachedhcp.c
@@ -67,8 +67,22 @@ static struct cached_dhcp_packet *cached_packets[] = {
 	&cached_pxebs,
 };
 
+/** Cached DHCP settings placeholder block */
+struct generic_settings cachedhcp_generic = {
+	.settings = {
+		.refcnt = NULL,
+		.name = "cachedhcp",
+		.siblings =
+		    LIST_HEAD_INIT ( cachedhcp_generic.settings.siblings ),
+		.children =
+		    LIST_HEAD_INIT ( cachedhcp_generic.settings.children ),
+		.op = &generic_settings_operations,
+	},
+	.list = LIST_HEAD_INIT ( cachedhcp_generic.list ),
+};
+
 /** Colour for debug messages */
-#define colour &cached_dhcpack
+#define colour &cachedhcp_settings
 
 /**
  * Free cached DHCP packet
@@ -114,6 +128,9 @@ static int cachedhcp_apply ( struct cached_dhcp_packet *cache,
 	/* Select appropriate parent settings block */
 	settings = ( netdev ? netdev_settings ( netdev ) : NULL );
 
+	/* Unregister from placeholder settings block */
+	unregister_settings ( &cache->dhcppkt->settings );
+
 	/* Register settings */
 	if ( ( rc = register_settings ( &cache->dhcppkt->settings, settings,
 					cache->name ) ) != 0 ) {
@@ -143,6 +160,7 @@ int cachedhcp_record ( struct cached_dhcp_packet *cache, userptr_t data,
 	struct dhcphdr *dhcphdr;
 	unsigned int i;
 	size_t len;
+	int rc;
 
 	/* Free any existing cached packet */
 	cachedhcp_free ( cache );
@@ -188,6 +206,14 @@ int cachedhcp_record ( struct cached_dhcp_packet *cache, userptr_t data,
 		}
 	}
 
+	/* Register in placeholder settings block */
+	if ( ( rc = register_settings ( &dhcppkt->settings, &cachedhcp_settings,
+					cache->name ) ) != 0 ) {
+		DBGC ( colour, "CACHEDHCP %s could not register placeholder "
+		       "settings: %s\n", cache->name, strerror ( rc ) );
+		return rc;
+	}
+
 	/* Store as cached packet */
 	DBGC ( colour, "CACHEDHCP %s at %#08lx+%#zx/%#zx\n", cache->name,
 	       user_to_phys ( data, 0 ), len, max_len );
diff --git a/src/core/settings.c b/src/core/settings.c
index fcdf98d2b..d81b2ffbf 100644
--- a/src/core/settings.c
+++ b/src/core/settings.c
@@ -526,6 +526,10 @@ void unregister_settings ( struct settings *settings ) {
 	DBGC ( settings, "Settings %p (\"%s\") unregistered\n",
 	       settings, settings_name ( settings ) );
 
+	/* Do nothing more if settings are already unregistered */
+	if ( ! settings->parent )
+		return;
+
 	/* Remove from list of settings */
 	ref_put ( settings->parent->refcnt );
 	settings->parent = NULL;
diff --git a/src/include/ipxe/cachedhcp.h b/src/include/ipxe/cachedhcp.h
index 39ce74543..7a48cfb62 100644
--- a/src/include/ipxe/cachedhcp.h
+++ b/src/include/ipxe/cachedhcp.h
@@ -17,6 +17,9 @@ struct cached_dhcp_packet;
 extern struct cached_dhcp_packet cached_dhcpack;
 extern struct cached_dhcp_packet cached_proxydhcp;
 extern struct cached_dhcp_packet cached_pxebs;
+extern struct generic_settings cachedhcp_generic;
+
+#define cachedhcp_settings cachedhcp_generic.settings
 
 extern int cachedhcp_record ( struct cached_dhcp_packet *cache, userptr_t data,
 			      size_t max_len );