[efi] Add efi_path_vlan() utility function

EFI provides no API for determining the VLAN tag (if any) for a
specified device handle.  There is the EFI_VLAN_CONFIG_PROTOCOL, but
that exists only on the trunk device handle (not on the VLAN device
handle), and provides no way to match VLAN tags against the trunk
device's child device handles.

The EDK2 codebase seems to rely solely on the device path to determine
the VLAN tag for a specified device handle: both NetLibGetVlanId() and
BmGetNetworkDescription() will parse the device path to search for a
VLAN_DEVICE_PATH component.

Add efi_path_vlan() which uses the same device path parsing logic to
determine the VLAN tag.

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

1 files changed, 23 insertions, 0 deletions

diff --git a/src/interface/efi/efi_path.c b/src/interface/efi/efi_path.c
index 937d3c70..fb0f3059 100644
--- a/src/interface/efi/efi_path.c
+++ b/src/interface/efi/efi_path.c
@@ -95,6 +95,29 @@ size_t efi_path_len ( EFI_DEVICE_PATH_PROTOCOL *path ) {
 }
 
 /**
+ * Get VLAN tag from device path
+ *
+ * @v path		Device path
+ * @ret tag		VLAN tag, or 0 if not a VLAN
+ */
+unsigned int efi_path_vlan ( EFI_DEVICE_PATH_PROTOCOL *path ) {
+	EFI_DEVICE_PATH_PROTOCOL *next;
+	VLAN_DEVICE_PATH *vlan;
+
+	/* Search for VLAN device path */
+	for ( ; ( next = efi_path_next ( path ) ) ; path = next ) {
+		if ( ( path->Type == MESSAGING_DEVICE_PATH ) &&
+		     ( path->SubType == MSG_VLAN_DP ) ) {
+			vlan = container_of ( path, VLAN_DEVICE_PATH, Header );
+			return vlan->VlanId;
+		}
+	}
+
+	/* No VLAN device path found */
+	return 0;
+}
+
+/**
  * Concatenate EFI device paths
  *
  * @v ...		List of device paths (NULL terminated)