aoe: failover remote interface based on aoe_deadsecs parameter

The aoe_deadsecs module parameter allows the user to specify a hard limit
on the number of seconds an AoE command can be retransmitted before the
AoE block device is considered to have failed.

Using aoe_deadsecs to determine the time we try using a different remote
interface helps to ensure that the hard limit is not reached before we've
tried to recover by sending to a different remote port.

As a data storage target, the AoE target is unambiguously identified by
its {major, minor} AoE address tuple, and an AoE target can have multiple
MAC addresses.  However, note that "target" in the driver code and
comments means a {major, minor, MAC address} tuple, as in "somewhere to
send packets".

Signed-off-by: Ed Cashin <ecashin@coraid.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/block/aoe/aoe.h

@@ -96,7 +96,6 @@ enum {
 	TIMERTICK = HZ / 10,
 	MINTIMER = HZ >> 2,
 	MAXTIMER = HZ << 1,
-	HELPWAIT = 20,
 };
 
 struct buf {

drivers/block/aoe/aoecmd.c

@@ -633,11 +633,9 @@ rexmit_timer(ulong vp)
 		list_del(pos);
 
 		t = f->t;
-		if (n > HELPWAIT) {
-			/* see if another target can help */
-			if (d->ntargets > 1)
-				d->htgt = t;
-		}
+		if (n > aoe_deadsecs/2)
+			d->htgt = t; /* see if another target can help */
+
 		if (t->nout == t->maxout) {
 			if (t->maxout > 1)
 				t->maxout--;