teach vfs_get_tree() to handle subtype, switch do_new_mount() to it

Roll the handling of subtypes into do_new_mount() and vfs_get_tree().  The
former determines any subtype string and hangs it off the fs_context; the
latter applies it.

Make do_new_mount() create, parameterise and commit an fs_context and
create a mount for itself rather than calling vfs_kern_mount().

[AV -- missing kstrdup()]
[AV -- ... and no kstrdup() if we get to setting ->s_submount - we
simply transfer it from fc, leaving NULL behind]
[AV -- constify ->s_submount, while we are at it]

Reviewed-by: David Howells <dhowells@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/namespace.c

@@ -2479,29 +2479,6 @@ static int do_move_mount(struct path *path, const char *old_name)
 	return err;
 }
 
-static struct vfsmount *fs_set_subtype(struct vfsmount *mnt, const char *fstype)
-{
-	int err;
-	const char *subtype = strchr(fstype, '.');
-	if (subtype) {
-		subtype++;
-		err = -EINVAL;
-		if (!subtype[0])
-			goto err;
-	} else
-		subtype = "";
-
-	mnt->mnt_sb->s_subtype = kstrdup(subtype, GFP_KERNEL);
-	err = -ENOMEM;
-	if (!mnt->mnt_sb->s_subtype)
-		goto err;
-	return mnt;
-
- err:
-	mntput(mnt);
-	return ERR_PTR(err);
-}
-
 /*
  * add a mount into a namespace's mount tree
  */
@@ -2557,7 +2534,9 @@ static int do_new_mount(struct path *path, const char *fstype, int sb_flags,
 {
 	struct file_system_type *type;
 	struct vfsmount *mnt;
-	int err;
+	struct fs_context *fc;
+	const char *subtype = NULL;
+	int err = 0;
 
 	if (!fstype)
 		return -EINVAL;
@@ -2566,23 +2545,59 @@ static int do_new_mount(struct path *path, const char *fstype, int sb_flags,
 	if (!type)
 		return -ENODEV;
 
-	mnt = vfs_kern_mount(type, sb_flags, name, data);
-	if (!IS_ERR(mnt) && (type->fs_flags & FS_HAS_SUBTYPE) &&
-	    !mnt->mnt_sb->s_subtype)
-		mnt = fs_set_subtype(mnt, fstype);
+	if (type->fs_flags & FS_HAS_SUBTYPE) {
+		subtype = strchr(fstype, '.');
+		if (subtype) {
+			subtype++;
+			if (!*subtype) {
+				put_filesystem(type);
+				return -EINVAL;
+			}
+		} else {
+			subtype = "";
+		}
+	}
 
+	fc = fs_context_for_mount(type, sb_flags);
 	put_filesystem(type);
-	if (IS_ERR(mnt))
-		return PTR_ERR(mnt);
+	if (IS_ERR(fc))
+		return PTR_ERR(fc);
+
+	if (subtype) {
+		fc->subtype = kstrdup(subtype, GFP_KERNEL);
+		if (!fc->subtype)
+			err = -ENOMEM;
+	}
+	if (!err && name) {
+		fc->source = kstrdup(name, GFP_KERNEL);
+		if (!fc->source)
+			err = -ENOMEM;
+	}
+	if (!err)
+		err = parse_monolithic_mount_data(fc, data);
+	if (!err)
+		err = vfs_get_tree(fc);
+	if (err)
+		goto out;
+
+	up_write(&fc->root->d_sb->s_umount);
+	mnt = vfs_create_mount(fc);
+	if (IS_ERR(mnt)) {
+		err = PTR_ERR(mnt);
+		goto out;
+	}
 
 	if (mount_too_revealing(mnt, &mnt_flags)) {
 		mntput(mnt);
-		return -EPERM;
+		err = -EPERM;
+		goto out;
 	}
 
 	err = do_add_mount(real_mount(mnt), path, mnt_flags);
 	if (err)
 		mntput(mnt);
+out:
+	put_fs_context(fc);
 	return err;
 }
 

fs/super.c

@@ -1262,6 +1262,11 @@ int vfs_get_tree(struct fs_context *fc)
 	sb = fc->root->d_sb;
 	WARN_ON(!sb->s_bdi);
 
+	if (fc->subtype && !sb->s_subtype) {
+		sb->s_subtype = fc->subtype;
+		fc->subtype = NULL;
+	}
+
 	/*
 	 * Write barrier is for super_cache_count(). We place it before setting
 	 * SB_BORN as the data dependency between the two functions is the

include/linux/fs.h

@@ -1447,7 +1447,7 @@ struct super_block {
 	 * Filesystem subtype.  If non-empty the filesystem type field
 	 * in /proc/mounts will be "type.subtype"
 	 */
-	char *s_subtype;
+	const char *s_subtype;
 
 	const struct dentry_operations *s_d_op; /* default d_op for dentries */