NFSv4.2: Fixup CLONE dest file size for zero-length count

[ Upstream commit 038efb6 ]

When holding a delegation, the NFS client optimizes away setting the
attributes of a file from the GETATTR in the compound after CLONE, and for
a zero-length CLONE we will end up setting the inode's size to zero in
nfs42_copy_dest_done().  Handle this case by computing the resulting count
from the server's reported size after CLONE's GETATTR.

Suggested-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Benjamin Coddington <bcodding@redhat.com>
Fixes: 94d202d ("NFSv42: Copy offload should update the file size when appropriate")
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

fs/nfs/nfs42proc.c

@@ -1077,6 +1077,9 @@ static int _nfs42_proc_clone(struct rpc_message *msg, struct file *src_f,
 	status = nfs4_call_sync(server->client, server, msg,
 				&args.seq_args, &res.seq_res, 0);
 	if (status == 0) {
+		/* a zero-length count means clone to EOF in src */
+		if (count == 0 && res.dst_fattr->valid & NFS_ATTR_FATTR_SIZE)
+			count = nfs_size_to_loff_t(res.dst_fattr->size) - dst_offset;
 		nfs42_copy_dest_done(dst_inode, dst_offset, count);
 		status = nfs_post_op_update_inode(dst_inode, res.dst_fattr);
 	}