[PATCH 1/2] fs: export sget_dev()

[Christian Brauner]

> Yeah, good point. Done.

>From fe40c7fe1a87814f92f9b1d0b9fb78ac69404c33 Mon Sep 17 00:00:00 2001
From: Christian Brauner <brauner at kernel.org>
Date: Tue, 29 Aug 2023 15:05:28 +0200
Subject: [PATCH 1/2] fs: export sget_dev()

They will be used for mtd devices as well.

Signed-off-by: Christian Brauner <brauner at kernel.org>
---
 fs/super.c         | 64 ++++++++++++++++++++++++++++++++--------------
 include/linux/fs.h |  1 +
 2 files changed, 46 insertions(+), 19 deletions(-)

diff --git a/fs/super.c b/fs/super.c
index ad7ac3a24d38..d27d80bf7c43 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -1371,6 +1371,50 @@ 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.
@@ -1429,23 +1473,6 @@ 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)
 {
@@ -1523,8 +1550,7 @@ 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);
 
diff --git a/include/linux/fs.h b/include/linux/fs.h
index ca8ceccde3d6..8a8d1cd5b0a9 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2274,6 +2274,7 @@ 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) \
-- 
2.34.1