[SCSI] fcoe: Use NETIF_F_FCOE_MTU flag to set up max frame size (lport->mfs)

Add a define of FCOE_MTU as 2158 bytes and use FCOE_MTU when the LLD is found
to support NETIF_F_FCOE_MTU. The lport->mfs is then calculated out of the
2158 FCOE_MTU. Otherwise, we stick with the netdev->mtu, i.e., LAN MTU. Also,
change the notification on NETDEV_CHANGEMTU event to bypass changing mfs when
LAN MTU is changed if NETIF_F_FCOE_MTU is supported.

Signed-off-by: Yi Zou <yi.zou@intel.com>
Signed-off-by: Robert Love <robert.w.love@intel.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>

drivers/scsi/fcoe/fcoe.c

@@ -439,8 +439,12 @@ static int fcoe_netdev_config(struct fc_lport *lp, struct net_device *netdev)
 	 * user-configured limit.  If the MFS is too low, fcoe_link_ok()
 	 * will return 0, so do this first.
 	 */
-	mfs = netdev->mtu - (sizeof(struct fcoe_hdr) +
-			     sizeof(struct fcoe_crc_eof));
+	mfs = netdev->mtu;
+	if (netdev->features & NETIF_F_FCOE_MTU) {
+		mfs = FCOE_MTU;
+		FCOE_NETDEV_DBG(netdev, "Supports FCOE_MTU of %d bytes\n", mfs);
+	}
+	mfs -= (sizeof(struct fcoe_hdr) + sizeof(struct fcoe_crc_eof));
 	if (fc_set_mfs(lp, mfs))
 		return -EINVAL;
 
@@ -1570,6 +1574,8 @@ static int fcoe_device_notification(struct notifier_block *notifier,
 	case NETDEV_CHANGE:
 		break;
 	case NETDEV_CHANGEMTU:
+		if (netdev->features & NETIF_F_FCOE_MTU)
+			break;
 		mfs = netdev->mtu - (sizeof(struct fcoe_hdr) +
 				     sizeof(struct fcoe_crc_eof));
 		if (mfs >= FC_MIN_MAX_FRAME)

drivers/scsi/fcoe/fcoe.h

@@ -40,6 +40,12 @@
 #define FCOE_MIN_XID		0x0000	/* the min xid supported by fcoe_sw */
 #define FCOE_MAX_XID		0x0FFF	/* the max xid supported by fcoe_sw */
 
+/*
+ * Max MTU for FCoE: 14 (FCoE header) + 24 (FC header) + 2112 (max FC payload)
+ * + 4 (FC CRC) + 4 (FCoE trailer) =  2158 bytes
+ */
+#define FCOE_MTU	2158
+
 unsigned int fcoe_debug_logging;
 module_param_named(debug_logging, fcoe_debug_logging, int, S_IRUGO|S_IWUSR);
 MODULE_PARM_DESC(debug_logging, "a bit mask of logging levels");