tree e7b6845a3d53c5b92350f1755b4e89418f0c351c
parent 87c961cb747fa55b664b76abfcb9d44c14ae851f
author Mikulas Patocka <mpatocka@redhat.com> 1281582840 +0100
committer Alasdair G Kergon <agk@redhat.com> 1281582840 +0100

dm: skip second flush on bio unsupported error

When processing barriers, skip the second flush if processing the bio
failed with -EOPNOTSUPP.  This can happen with discard+barrier requests.
If the device doesn't support discard, there would be two useless
SYNCHRONIZE CACHE commands.  The first dm_flush cannot be so easily
optimized out, so we leave it there.

Previously, -EOPNOTSUPP could be received in dec_pending only with empty
barriers and we ignored that error, assuming the device not supporting
cache flushes has cache always consistent.  With the addition of discard
barriers, this -EOPNOTSUPP can also be generated by discards and we
must record it in md->barrier_error for process_barrier.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>