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author | Denis V. Lunev <den@openvz.org> | 2015-01-30 11:42:16 +0300 |
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committer | Kevin Wolf <kwolf@redhat.com> | 2015-02-06 17:24:20 +0100 |
commit | 1cdc3239f1bb8c8f18954defe3cb813edc9df4a0 (patch) | |
tree | 75184541dad76f196775dc024e7ab89aca9cc554 /qemu-img.c | |
parent | d50d82221934696633296975aa433fe8aeeac714 (diff) | |
download | hqemu-1cdc3239f1bb8c8f18954defe3cb813edc9df4a0.zip hqemu-1cdc3239f1bb8c8f18954defe3cb813edc9df4a0.tar.gz |
block: use fallocate(FALLOC_FL_PUNCH_HOLE) & fallocate(0) to write zeroes
This sequence works efficiently if FALLOC_FL_ZERO_RANGE is not supported.
Unfortunately, FALLOC_FL_ZERO_RANGE is supported on really modern systems
and only for a couple of filesystems. FALLOC_FL_PUNCH_HOLE is much more
mature.
The sequence of 2 operations FALLOC_FL_PUNCH_HOLE and 0 is necessary due
to the following reasons:
- FALLOC_FL_PUNCH_HOLE creates a hole in the file, the file becomes
sparse. In order to retain original functionality we must allocate
disk space afterwards. This is done using fallocate(0) call
- fallocate(0) without preceeding FALLOC_FL_PUNCH_HOLE will do nothing
if called above already allocated areas of the file, i.e. the content
will not be zeroed
This should increase the performance a bit for not-so-modern kernels.
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>
Signed-off-by: Denis V. Lunev <den@openvz.org>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Diffstat (limited to 'qemu-img.c')
0 files changed, 0 insertions, 0 deletions