generic: test for fsync after fallocate

Test that fsync operations preserve extents allocated with
fallocate(2) that are placed beyond a file's size.

This test is motivated by a bug found in btrfs where unwritten
extents beyond the inode's i_size were not preserved after a fsync
and power failure. The btrfs bug is fixed by the following patch for
the linux kernel:

 "Btrfs: fix loss of prealloc extents past i_size after fsync log replay"

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>
3 files changed