[Qemu-devel] [PATCH for-2.8 0/2] pass partial discard requests all the way down

[Eric Blake]

Peter reported a mild regression in qemu 2.7 when targetting the
Dell Equallogic iSCSI, which advertizes a preferred and maximum
unmap alignment at 15M.  In qemu 2.6, trims not aligned to those
boundaries still made it to the device, but in 2.7, the block
layer is ignoring unaligned portions of guest requests, resulting
in fewer blocks being actually trimmed.

Since discard is advisary, it is borderline if this counts as a
bug fix worthy for inclusion in 2.8, or if it should be deferred
to 2.9.  At any rate, while I was able to test that the patch
didn't misbehave for me when I tweaked an NBD setup to force
15M alignment, I am unable to test that it makes an actual
difference for Peter's hardware, and that needs to happen before
anyone even thinks of applying this.

Eric Blake (2):
  block: Return -ENOTSUP rather than assert on unaligned discards
  block: Pass unaligned discard requests to drivers

 block/io.c       | 36 +++++++++++++++++++++++-------------
 block/iscsi.c    |  4 +++-
 block/qcow2.c    |  4 ++++
 block/sheepdog.c |  5 +++--
 4 files changed, 33 insertions(+), 16 deletions(-)

-- 
2.7.4