[Qemu-devel] [PATCH v6 0/7] eliminate data write in bdrv_write_zeroes on Linux in raw-posix.c

["Denis V. Lunev" <den@openvz.org>]

I have performed several tests with non-aligned fallocate calls and
in all cases (with non-aligned fallocates) Linux performs fine, i.e.
areas are zeroed correctly. Checks were made on
Linux 3.16.0-28-generic #38-Ubuntu SMP

This should seriously increase performance of bdrv_write_zeroes

Changes from v5:
- changed order between patches 5/6
- check has_fallocate in FALLOC_FL_PUNCH_HOLE branch of the code
- minor comment tweaks as pointed out by Max Reitz

Changes from v4:
- comments to patches are improved by Max Reitz suggestions
- replaced 'return ret' with 'return -ENOTSUP' handle_aiocb_write_zeroes
  The idea is that we can reach that point only if original ret was
  equal to -ENOTSUP
- added has_fallocate flag to indicate that fallocate is working for
  given BDS
- checked file length with bdrv_getlength

Changes from v3:
- dropped original patch 1, equivalent stuff was merged already
- reordered patches as suggested by Fam
- fixes spelling errors as suggested by Fam
- fixed not initialized value in handle_aiocb_write_zeroes
- fixed wrong error processing from do_fallocate(FALLOC_FL_ZERO_RANGE)

Changes from v2:
- added Peter Lieven to CC
- added CONFIG_FALLOCATE check to call do_fallocate in patch 7
- dropped patch 1 as NACK-ed
- added processing of very large data areas in bdrv_co_write_zeroes (new
  patch 1)
- set bl.max_write_zeroes to INT_MAX in raw-posix.c for regular files
  (new patch 8)

Signed-off-by: Denis V. Lunev <den@openvz.org>
CC: Max Reitz <mreitz@redhat.com>
CC: Kevin Wolf <kwolf@redhat.com>
CC: Stefan Hajnoczi <stefanha@redhat.com>
CC: Peter Lieven <pl@kamp.de>
CC: Fam Zheng <famz@redhat.com>