[patch amendment] ieee1394: survive a few seconds connection loss

[Stefan Richter]

On 19 Aug, Stefan Richter wrote:
> There are situations when nodes vanish from the bus and come back in
> quickly thereafter:
>   - When certain bus-powered hubs are plugged in,
>   - when certain disk enclosures are switched from self-power to bus
>     power or vice versa and break the daisy chain during the transition,
>   - when the user plugs a cable out and quickly plugs it back in, e.g.
>     to reorder a daisy chain (works on Mac OS X if done quickly enough),
>   - when certain hubs temporarily malfunction during high bus traffic.
> 
> The ieee1394 driver's nodemgr already contained a function to set
> vanished nodes aside into "limbo"; i.e. they wouldn't actually be
> deleted right away.  (In fact, only unloading the driver or writing into
> an obscure sysfs attribute would delete them eventually.)  If nodes
> reappeared later, they would be resurrected out of limbo.
> 
> Moving nodes into and out of limbo was accompanied with calling the
> .suspend() and .resume() driver methods of the drivers which were bound
> to a respective node's unit directories.  Not only is this somewhat
> strange due to the primary use of these drivers for power management,
> also the sbp2 driver in particular does not implement .suspend() and
> .resume().
> 
> Hence sbp2 would be disconnected from devices in situations as listed
> above.
> 
> We now:
>   - leave drivers bound when nodes go into limbo,
>   - call the drivers' .update() when nodes come out of limbo,
>   - automatically delete in-limbo nodes 5 seconds after the last
>     bus reset and bus rescan.
>   - Because of the automatic removal, the now obsolete bus attribute
>     /sys/bus/ieee1394/destroy_node is removed.
> 
> This especially lets sbp2 survive brief disconnections.  You can for
> example yank a disk's cable and plug it back in while reading the
> respective disk with dd, but dd will happily continue as if nothing
> happened.

Amendment:  Reduce timeout from 5 to 3 seconds.  This is enough because
the timeout is restarted if another bus reset happened during the
timeout.

Signed-off-by: Stefan Richter <stefanr@xxxxxxxxxxxxxxxxx>
---
 drivers/ieee1394/nodemgr.c |    9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

Index: linux/drivers/ieee1394/nodemgr.c
===================================================================
--- linux.orig/drivers/ieee1394/nodemgr.c
+++ linux/drivers/ieee1394/nodemgr.c
@@ -1726,18 +1726,17 @@ static int nodemgr_host_thread(void *dat
 		/* Update some of our sysfs symlinks */
 		nodemgr_update_host_dev_links(host);
 
-		/* Sleep 5 seconds */
-		for (i = 0; i < 5000/100 ; i++) {
-			msleep_interruptible(100);
+		/* Sleep 3 seconds */
+		for (i = 3000/200; i; i--) {
+			msleep_interruptible(200);
 			if (kthread_should_stop())
 				goto exit;
 
 			if (generation != get_hpsb_generation(host))
 				break;
 		}
-
 		/* Remove nodes which are gone, unless a bus reset happened */
-		if (i == 5000/100)
+		if (!i)
 			nodemgr_remove_nodes_in_limbo(host);
 	}
 exit:


-- 
Stefan Richter
-=====-==--- =-=- -=-=-
http://arcgraph.de/sr/

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