syscalls/fallocate04: Fix on Btrfs
The size of a file can increase on Btrfs temporarily even when we write
into a preallocated space because of internal Btrfs caches, at least
that is what I've been told by Btrfs devs. The internal caches are then
freed after some time, or can be force freed by syncing the file, which
is what this patch does.
Technically we are not guaranteed that the file size will not change
after writing to preallocated space. We are only guaranteed that
subsequent writes to the region will not fail with ENOSPC. So this
behavior, while uncommon, is not really a bug.
Before the patch the test fails with:
fallocate04 0 TINFO : allocate '12288' bytes
fallocate04 1 TPASS : test-case succeeded
fallocate04 0 TINFO : read allocated file size '24576'
fallocate04 0 TINFO : make a hole with FALLOC_FL_PUNCH_HOLE
fallocate04 0 TINFO : check that file has a hole with lseek(,,SEEK_HOLE)
fallocate04 0 TINFO : found a hole at '4096' offset
fallocate04 0 TINFO : allocated file size before '24576' and after '12288'
fallocate04 2 TFAIL : fallocate04.c:184: not expected allocated size
Signed-off-by: Cyril Hrubis <chrubis@suse.cz>
Tested-by: Stanislav Kholmanskikh <stanislav.kholmanskikh@oracle.com>
1 file changed