fs: export sget_dev()

They will be used for mtd devices as well.
Acked-by: Richard Weinberger <richard@nod.at>
Reviewed-by: Jan Kara <jack@suse.cz>
Message-Id: <20230829-vfs-super-mtd-v1-1-fecb572e5df3@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner <brauner@kernel.org>

fs/super.c

@@ -1373,6 +1373,50 @@ int get_tree_keyed(struct fs_context *fc,
 }
 EXPORT_SYMBOL(get_tree_keyed);
 
+static int set_bdev_super(struct super_block *s, void *data)
+{
+	s->s_dev = *(dev_t *)data;
+	return 0;
+}
+
+static int super_s_dev_set(struct super_block *s, struct fs_context *fc)
+{
+	return set_bdev_super(s, fc->sget_key);
+}
+
+static int super_s_dev_test(struct super_block *s, struct fs_context *fc)
+{
+	return !(s->s_iflags & SB_I_RETIRED) &&
+		s->s_dev == *(dev_t *)fc->sget_key;
+}
+
+/**
+ * sget_dev - Find or create a superblock by device number
+ * @fc: Filesystem context.
+ * @dev: device number
+ *
+ * Find or create a superblock using the provided device number that
+ * will be stored in fc->sget_key.
+ *
+ * If an extant superblock is matched, then that will be returned with
+ * an elevated reference count that the caller must transfer or discard.
+ *
+ * If no match is made, a new superblock will be allocated and basic
+ * initialisation will be performed (s_type, s_fs_info, s_id, s_dev will
+ * be set). The superblock will be published and it will be returned in
+ * a partially constructed state with SB_BORN and SB_ACTIVE as yet
+ * unset.
+ *
+ * Return: an existing or newly created superblock on success, an error
+ *         pointer on failure.
+ */
+struct super_block *sget_dev(struct fs_context *fc, dev_t dev)
+{
+	fc->sget_key = &dev;
+	return sget_fc(fc, super_s_dev_test, super_s_dev_set);
+}
+EXPORT_SYMBOL(sget_dev);
+
 #ifdef CONFIG_BLOCK
 /*
  * Lock a super block that the callers holds a reference to.
@@ -1431,23 +1475,6 @@ const struct blk_holder_ops fs_holder_ops = {
 };
 EXPORT_SYMBOL_GPL(fs_holder_ops);
 
-static int set_bdev_super(struct super_block *s, void *data)
-{
-	s->s_dev = *(dev_t *)data;
-	return 0;
-}
-
-static int set_bdev_super_fc(struct super_block *s, struct fs_context *fc)
-{
-	return set_bdev_super(s, fc->sget_key);
-}
-
-static int test_bdev_super_fc(struct super_block *s, struct fs_context *fc)
-{
-	return !(s->s_iflags & SB_I_RETIRED) &&
-		s->s_dev == *(dev_t *)fc->sget_key;
-}
-
 int setup_bdev_super(struct super_block *sb, int sb_flags,
 		struct fs_context *fc)
 {
@@ -1525,8 +1552,7 @@ int get_tree_bdev(struct fs_context *fc,
 	}
 
 	fc->sb_flags |= SB_NOSEC;
-	fc->sget_key = &dev;
-	s = sget_fc(fc, test_bdev_super_fc, set_bdev_super_fc);
+	s = sget_dev(fc, dev);
 	if (IS_ERR(s))
 		return PTR_ERR(s);
 

include/linux/fs.h

@@ -2397,6 +2397,7 @@ struct super_block *sget(struct file_system_type *type,
 			int (*test)(struct super_block *,void *),
 			int (*set)(struct super_block *,void *),
 			int flags, void *data);
+struct super_block *sget_dev(struct fs_context *fc, dev_t dev);
 
 /* Alas, no aliases. Too much hassle with bringing module.h everywhere */
 #define fops_get(fops) \