generic/563: tolerate small reads in "write -> read/write" sub-test
On ext2/ext3, it's expected that several single block metadata reads
can occur when writing to file in the same cgroup (the stack is like
below[1]). The purpose of the "write -> read/write" subtest is to
make sure the larger pwrite is accounted to the correct cgroup, not
necessarily enforce that zero bytes are read in service of the
write. This patch fixes the sub-test in order to tolerate small
reads in 1st cgroup.
[1] Callchain of the read:
@ext3_read_bio[
submit_bio+1
submit_bh_wbc+365
ext4_read_bh+72
ext4_get_branch+201
ext4_ind_map_blocks+382
ext4_map_blocks+295
_ext4_get_block+170
__block_write_begin_int+328
ext4_write_begin+541
generic_perform_write+213
ext4_buffered_write_iter+167
new_sync_write+345
vfs_write+438
__x64_sys_pwrite64+140
do_syscall_64+51
entry_SYSCALL_64_after_hwframe+68
, 5793, 12]: 3
Signed-off-by: Boyang Xue <bxue@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>