virtio-fs: don't show mount options

Virtio-fs does not accept any mount options, so it's confusing and wrong to
show any in /proc/mounts.

Reported-by: Stefan Hajnoczi <stefanha@redhat.com> 
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/fuse/fuse_i.h

@@ -479,6 +479,7 @@ struct fuse_fs_context {
 	bool destroy:1;
 	bool no_control:1;
 	bool no_force_umount:1;
+	bool no_mount_options:1;
 	unsigned int max_read;
 	unsigned int blksize;
 	const char *subtype;
@@ -713,6 +714,9 @@ struct fuse_conn {
 	/** Do not allow MNT_FORCE umount */
 	unsigned int no_force_umount:1;
 
+	/* Do not show mount options */
+	unsigned int no_mount_options:1;
+
 	/** The number of requests waiting for completion */
 	atomic_t num_waiting;
 

fs/fuse/inode.c

@@ -558,6 +558,9 @@ static int fuse_show_options(struct seq_file *m, struct dentry *root)
 	struct super_block *sb = root->d_sb;
 	struct fuse_conn *fc = get_fuse_conn_super(sb);
 
+	if (fc->no_mount_options)
+		return 0;
+
 	seq_printf(m, ",user_id=%u", from_kuid_munged(fc->user_ns, fc->user_id));
 	seq_printf(m, ",group_id=%u", from_kgid_munged(fc->user_ns, fc->group_id));
 	if (fc->default_permissions)
@@ -1180,6 +1183,7 @@ int fuse_fill_super_common(struct super_block *sb, struct fuse_fs_context *ctx)
 	fc->destroy = ctx->destroy;
 	fc->no_control = ctx->no_control;
 	fc->no_force_umount = ctx->no_force_umount;
+	fc->no_mount_options = ctx->no_mount_options;
 
 	err = -ENOMEM;
 	root = fuse_get_root_inode(sb, ctx->rootmode);

fs/fuse/virtio_fs.c

@@ -992,6 +992,7 @@ static int virtio_fs_fill_super(struct super_block *sb)
 		.destroy = true,
 		.no_control = true,
 		.no_force_umount = true,
+		.no_mount_options = true,
 	};
 
 	mutex_lock(&virtio_fs_mutex);