fs: indicate request originates from old mount API

[ Upstream commit f67d922edb4e95a4a56d07d5d40a76dd4f23a85b ]

We already communicate to filesystems when a remount request comes from
the old mount API as some filesystems choose to implement different
behavior in the new mount API than the old mount API to e.g., take the
chance to fix significant API bugs. Allow the same for regular mount
requests.

Fixes: b330966f79 ("fuse: reject options on reconfigure via fsconfig(2)")
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

fs/namespace.c

@@ -2647,7 +2647,12 @@ static int do_remount(struct path *path, int ms_flags, int sb_flags,
 	if (IS_ERR(fc))
 		return PTR_ERR(fc);
 
+	/*
+	 * Indicate to the filesystem that the remount request is coming
+	 * from the legacy mount system call.
+	 */
 	fc->oldapi = true;
+
 	err = parse_monolithic_mount_data(fc, data);
 	if (!err) {
 		down_write(&sb->s_umount);
@@ -2981,6 +2986,12 @@ static int do_new_mount(struct path *path, const char *fstype, int sb_flags,
 	if (IS_ERR(fc))
 		return PTR_ERR(fc);
 
+	/*
+	 * Indicate to the filesystem that the mount request is coming
+	 * from the legacy mount system call.
+	 */
+	fc->oldapi = true;
+
 	if (subtype)
 		err = vfs_parse_fs_string(fc, "subtype",
 					  subtype, strlen(subtype));