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.
Signed-off-by: Denis V. Lunev <address@hidden>
CC: Max Reitz <address@hidden>
CC: Kevin Wolf <address@hidden>
CC: Stefan Hajnoczi <address@hidden>
CC: Peter Lieven <address@hidden>
CC: Fam Zheng <address@hidden>
---
block/raw-posix.c | 19 +++++++++++++++++++
1 file changed, 19 insertions(+)