vfs_get_super() already implements the common get_tree pattern of
looking up an existing superblock via a test callback and initialising
a new one with fill_super otherwise, but it is private to fs/super.c
and only reachable through the get_tree_nodev()/get_tree_single()/
get_tree_keyed() wrappers, none of which let a filesystem supply its
own test callback.

Rename it to get_tree_super() and export it so filesystems that need a
custom superblock matching policy can reuse it directly instead of
open-coding sget_fc() + fill_super().  No functional change.

This is a preparatory fix for the next patch.

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>
---
 fs/super.c                 | 19 +++++++++++++++----
 include/linux/fs_context.h |  4 ++++
 2 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/fs/super.c b/fs/super.c
index a8fd61136aaf..84b878317364 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -1251,7 +1251,17 @@ static int test_single_super(struct super_block *s, struct fs_context *fc)
 	return 1;
 }
 
-static int vfs_get_super(struct fs_context *fc,
+/**
+ * get_tree_super - Get a superblock, optionally sharing an existing one
+ * @fc: The filesystem context holding the parameters
+ * @test: Comparison function to find a matching existing superblock, or NULL
+ * @fill_super: Helper to initialise a new superblock
+ *
+ * If @test is non-NULL and matches an existing superblock, that superblock is
+ * reused; otherwise a new anonymous superblock is created and initialised with
+ * @fill_super.  Passing NULL for @test always creates a new superblock.
+ */
+int get_tree_super(struct fs_context *fc,
 		int (*test)(struct super_block *, struct fs_context *),
 		int (*fill_super)(struct super_block *sb,
 				  struct fs_context *fc))
@@ -1278,12 +1288,13 @@ static int vfs_get_super(struct fs_context *fc,
 	deactivate_locked_super(sb);
 	return err;
 }
+EXPORT_SYMBOL(get_tree_super);
 
 int get_tree_nodev(struct fs_context *fc,
 		  int (*fill_super)(struct super_block *sb,
 				    struct fs_context *fc))
 {
-	return vfs_get_super(fc, NULL, fill_super);
+	return get_tree_super(fc, NULL, fill_super);
 }
 EXPORT_SYMBOL(get_tree_nodev);
 
@@ -1291,7 +1302,7 @@ int get_tree_single(struct fs_context *fc,
 		  int (*fill_super)(struct super_block *sb,
 				    struct fs_context *fc))
 {
-	return vfs_get_super(fc, test_single_super, fill_super);
+	return get_tree_super(fc, test_single_super, fill_super);
 }
 EXPORT_SYMBOL(get_tree_single);
 
@@ -1301,7 +1312,7 @@ int get_tree_keyed(struct fs_context *fc,
 		void *key)
 {
 	fc->s_fs_info = key;
-	return vfs_get_super(fc, test_keyed_super, fill_super);
+	return get_tree_super(fc, test_keyed_super, fill_super);
 }
 EXPORT_SYMBOL(get_tree_keyed);
 
diff --git a/include/linux/fs_context.h b/include/linux/fs_context.h
index 0d6c8a6d7be2..c920aba5177c 100644
--- a/include/linux/fs_context.h
+++ b/include/linux/fs_context.h
@@ -150,6 +150,10 @@ extern int vfs_parse_fs_param_source(struct fs_context *fc,
 				     struct fs_parameter *param);
 extern void fc_drop_locked(struct fs_context *fc);
 
+extern int get_tree_super(struct fs_context *fc,
+			 int (*test)(struct super_block *, struct fs_context *),
+			 int (*fill_super)(struct super_block *sb,
+					   struct fs_context *fc));
 extern int get_tree_nodev(struct fs_context *fc,
 			 int (*fill_super)(struct super_block *sb,
 					   struct fs_context *fc));
-- 
2.55.0