[stp] Add support for detecting Spanning Tree Protocol non-forwarding ports

A fairly common end-user problem is that the default configuration of
a switch may leave the port in a non-forwarding state for a
substantial length of time (tens of seconds) after link up.  This can
cause iPXE to time out and give up attempting to boot.

We cannot force the switch to start forwarding packets sooner, since
any attempt to send a Spanning Tree Protocol bridge PDU may cause the
switch to disable our port (if the switch happens to have the Bridge
PDU Guard feature enabled for the port).

For non-ancient versions of the Spanning Tree Protocol, we can detect
whether or not the port is currently forwarding and use this to inform
the network device core that the link is currently blocked.

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

2 files changed, 77 insertions, 0 deletions

diff --git a/src/include/ipxe/errfile.h b/src/include/ipxe/errfile.h
index d217eea0..97d55573 100644
--- a/src/include/ipxe/errfile.h
+++ b/src/include/ipxe/errfile.h
@@ -243,6 +243,7 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 #define ERRFILE_nfs_uri			( ERRFILE_NET | 0x003c0000 )
 #define ERRFILE_rndis			( ERRFILE_NET | 0x003d0000 )
 #define ERRFILE_pccrc			( ERRFILE_NET | 0x003e0000 )
+#define ERRFILE_stp			( ERRFILE_NET | 0x003f0000 )
 
 #define ERRFILE_image		      ( ERRFILE_IMAGE | 0x00000000 )
 #define ERRFILE_elf		      ( ERRFILE_IMAGE | 0x00010000 )
diff --git a/src/include/ipxe/stp.h b/src/include/ipxe/stp.h
new file mode 100644
index 00000000..3d85e5ba
--- /dev/null
+++ b/src/include/ipxe/stp.h
@@ -0,0 +1,76 @@
+#ifndef _IPXE_STP_H
+#define _IPXE_STP_H
+
+/** @file
+ *
+ * Spanning Tree Protocol (STP)
+ *
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
+
+#include <stdint.h>
+#include <ipxe/if_ether.h>
+
+/** "Protocol" value for STP
+ *
+ * This is the concatenated {DSAP,SSAP} value used internally by iPXE
+ * as the network-layer protocol for LLC frames.
+ */
+#define ETH_P_STP 0x4242
+
+/** A switch identifier */
+struct stp_switch {
+	/** Priotity */
+	uint16_t priority;
+	/** MAC address */
+	uint8_t mac[ETH_ALEN];
+} __attribute__ (( packed ));
+
+/** A Spanning Tree bridge protocol data unit */
+struct stp_bpdu {
+	/** LLC DSAP */
+	uint8_t dsap;
+	/** LLC SSAP */
+	uint8_t ssap;
+	/** LLC control field */
+	uint8_t control;
+	/** Protocol ID */
+	uint16_t protocol;
+	/** Protocol version */
+	uint8_t version;
+	/** Message type */
+	uint8_t type;
+	/** Flags */
+	uint8_t flags;
+	/** Root switch */
+	struct stp_switch root;
+	/** Root path cost */
+	uint32_t cost;
+	/** Sender switch */
+	struct stp_switch sender;
+	/** Port */
+	uint16_t port;
+	/** Message age */
+	uint16_t age;
+	/** Maximum age */
+	uint16_t max;
+	/** Hello time */
+	uint16_t hello;
+	/** Forward delay */
+	uint16_t delay;
+} __attribute__ (( packed ));
+
+/** Spanning Tree protocol ID */
+#define STP_PROTOCOL 0x0000
+
+/** Rapid Spanning Tree protocol version */
+#define STP_VERSION_RSTP 0x02
+
+/** Rapid Spanning Tree bridge PDU type */
+#define STP_TYPE_RSTP 0x02
+
+/** Port is forwarding */
+#define STP_FL_FORWARDING 0x20
+
+#endif /* _IPXE_STP_H */