aoe: allow user to disable target failure timeout

With this change, the aoe driver treats the value zero as special for
the aoe_deadsecs module parameter. Normally, this value specifies the
number of seconds during which the driver will continue to attempt
retransmits to an unresponsive AoE target. After aoe_deadsecs has
elapsed, the aoe driver marks the aoe device as "down" and fails all
I/O.

The new meaning of an aoe_deadsecs of zero is for the driver to
retransmit commands indefinitely.

Signed-off-by: Ed Cashin <[e-mail]>
Cc: Jens Axboe <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

Documentation/aoe/aoe.txt

···
   The aoe_deadsecs module parameter determines the maximum number of
   seconds that the driver will wait for an AoE device to provide a
   response to an AoE command.  After aoe_deadsecs seconds have
-  elapsed, the AoE device will be marked as "down".
+  elapsed, the AoE device will be marked as "down".  A value of zero
+  is supported for testing purposes and makes the aoe driver keep
+  trying AoE commands forever.
 
   The aoe_maxout module parameter has a default of 128.  This is the
   maximum number of unresponded packets that will be sent to an AoE

drivers/block/aoe/aoecmd.c

···
 		since = tsince_hr(f);
 		n = f->waited_total + since;
 		n /= USEC_PER_SEC;
-		if (n > aoe_deadsecs && !(f->flags & FFL_PROBE)) {
+		if (aoe_deadsecs
+		&& n > aoe_deadsecs
+		&& !(f->flags & FFL_PROBE)) {
 			/* Waited too long.  Device failure.
 			 * Hang all frames on first hash bucket for downdev
 			 * to clean up.