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[0/1] Use real FS block size in fallocate05

Message ID 20191128093610.6903-1-mdoucha@suse.cz
Headers show
Series Use real FS block size in fallocate05 | expand

Message

Martin Doucha Nov. 28, 2019, 9:36 a.m. UTC 
Using fixed-size buffer in fallocate05 caused some failures in the past
due to allocation requests being misaligned with actual file system blocks.
Btrfs in particular will treat misaligned allocation as regular write()
and apply copy-on-write to partially allocated blocks even on the first real
write().

While that behavior is somewhat surprising, it does make sense. Fix the error
by using multiples of real block size in fallocate() and write().

I've also found some XFS and Btrfs quirks which are documented in the patch.
The XFS behavior appears to be intentional. I'm still waiting for reply
whether the Btrfs quirk with deallocating blocks is a bug or not.

I'll also write another fallocate() test later for checking FS behavior
on intentionally misaligned allocation. But this fix can be committed before
that.

Martin Doucha (1):
  Use real FS block size in fallocate05

 .../kernel/syscalls/fallocate/fallocate05.c   | 75 ++++++++++++-------
 1 file changed, 50 insertions(+), 25 deletions(-)