[Qemu-devel] [PATCH v3 0/8] eliminate data write in bdrv_write_zeroes on Linux in raw-posix.c

[Denis V. Lunev]

These patches eliminate data writes completely on Linux if fallocate
FALLOC_FL_ZERO_RANGE or FALLOC_FL_PUNCH_HOLE are  supported on
underlying filesystem.

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 in some special cases.

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 <address@hidden>
CC: Kevin Wolf <address@hidden>
CC: Stefan Hajnoczi <address@hidden>
CC: Peter Lieven <address@hidden>