do_fallocate with (FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE) is not necessary when allocate a new qcow2 cluster

[ChangLimin]

From commit https://git.qemu.org/?p=qemu.git;a=commit;h=c8bb23cbdbe32f5c326365e0a82e1b0e68cdcd8a 

for qcow2 file in ocfs2 filesystem, do_fallocate with (FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE) 

will be called when allocate a new cluster.  It's not necessary and also cause data error.

1. create a ocfs2 cluster and   `mkfs.ocfs2 -b 4k -C 1M -N 2 /dev/sdb1`  then `mount /dev/sdb1 /mnt`

2. qemu-img create -f qcow2 -o cluster_size=256k /mnt/test.img 1G

3. attach /mnt/test.img to a linux vm as vdb

4. in vm, `dd if=/root/foo of=/dev/vdb bs=4k count=1` 

5. `hexdump -C /dev/vdb -n 4096`   the output is not identical to the file /root/foo

After remove do_fallocate with (FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE) in handle_aiocb_write_zeroes , 

it's good.

Chang Limin