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dm mpath: switch paths in dm_blk_ioctl() code path

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SCSI LUN passthrough code such as qemu's "scsi-block" device model
pass every IO to the host via SG_IO ioctls. Currently, dm-multipath
calls choose_pgpath() only in the block IO code path, not in the ioctl
code path (unless current_pgpath is NULL). This has the effect that no
path switching and thus no load balancing is done for SCSI-passthrough
IO, unless the active path fails.

Fix this by using the same logic in multipath_prepare_ioctl() as in
multipath_clone_and_map().

Note: The allegedly best path selection algorithm, service-time,
still wouldn't work perfectly, because the io size of the current
request is always set to 0. Changing that for the IO passthrough
case would require the ioctl cmd and arg to be passed to dm's
prepare_ioctl() method.

Signed-off-by: Martin Wilck <mwilck@suse.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
This commit is contained in:
Martin Wilck 2020-04-20 22:29:09 +02:00 committed by Mike Snitzer
parent 27f5411a71
commit 2361ae5953
1 changed files with 1 additions and 1 deletions
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2
drivers/md/dm-mpath.c
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@ -1918,7 +1918,7 @@ static int multipath_prepare_ioctl(struct dm_target *ti,
int r;
current_pgpath = READ_ONCE(m->current_pgpath);
if (!current_pgpath)
if (!current_pgpath || !test_bit(MPATHF_QUEUE_IO, &m->flags))
current_pgpath = choose_pgpath(m, 0);
if (current_pgpath) {