cifs: have find_readable/writable_file filter by fsuid

When we implement multiuser mounts, we'll need to filter filehandles
by fsuid. Add a flag for multiuser mounts and code to filter by
fsuid when it's set.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>
diff --git a/fs/cifs/inode.c b/fs/cifs/inode.c
index a39a1c4..df29a3a 100644
--- a/fs/cifs/inode.c
+++ b/fs/cifs/inode.c
@@ -963,7 +963,7 @@
 	/*
 	 * If the file is already open for write, just use that fileid
 	 */
-	open_file = find_writable_file(cifsInode);
+	open_file = find_writable_file(cifsInode, true);
 	if (open_file) {
 		netfid = open_file->netfid;
 		netpid = open_file->pid;
@@ -1813,7 +1813,7 @@
 	 * writebehind data than the SMB timeout for the SetPathInfo
 	 * request would allow
 	 */
-	open_file = find_writable_file(cifsInode);
+	open_file = find_writable_file(cifsInode, true);
 	if (open_file) {
 		__u16 nfid = open_file->netfid;
 		__u32 npid = open_file->pid;
@@ -1978,7 +1978,7 @@
 		args->ctime = NO_CHANGE_64;
 
 	args->device = 0;
-	open_file = find_writable_file(cifsInode);
+	open_file = find_writable_file(cifsInode, true);
 	if (open_file) {
 		u16 nfid = open_file->netfid;
 		u32 npid = open_file->pid;