ceph: Implement writev/pwritev for sync operation.
ceph: Implement writev/pwritev for sync operation.

For writev/pwritev sync-operatoin, ceph only do the first iov.

I divided the write-sync-operation into two functions. One for
direct-write, other for none-direct-sync-write. This is because for
none-direct-sync-write we can merge iovs to one. But for direct-write,
we can't merge iovs.

Signed-off-by: Jianpeng Ma <c2efc80ba27cf31d4676f82b7232757b76911f7a@gmail.com>
Reviewed-by: Yan, Zheng <45e2ee8c8b09e76a9d512320d4eb53c0cd9925c0@intel.com>
Signed-off-by: Sage Weil <6dd34506bbd5e58221bbb3e4732d97c91f02277b@inktank.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs