[PATCH v2 1/2] fs/super.c: introduce get_tree_bdev_flags()

[Gao Xiang]

As Allison reported [1], currently get_tree_bdev() will store
"Can't lookup blockdev" error message.  Although it makes sense for
pure bdev-based fses, this message may mislead users who try to use
EROFS file-backed mounts since get_tree_nodev() is used as a fallback
then.

Add get_tree_bdev_flags() to specify extensible flags [2] and
GET_TREE_BDEV_QUIET_LOOKUP to silence "Can't lookup blockdev" message
since it's misleading to EROFS file-backed mounts now.

[1] https://lore.kernel.org/r/CAOYeF9VQ8jKVmpy5Zy9DNhO6xmWSKMB-DO8yvBB0XvBE7=3Ugg@xxxxxxxxxxxxxx
[2] https://lore.kernel.org/r/ZwUkJEtwIpUA4qMz@xxxxxxxxxxxxx
Suggested-by: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Signed-off-by: Gao Xiang <hsiangkao@xxxxxxxxxxxxxxxxx>
---
v1: https://lore.kernel.org/r/20241008095606.990466-1-hsiangkao@xxxxxxxxxxxxxxxxx
change since v1:
 - add get_tree_bdev_flags() suggested by Christoph.

 fs/super.c                 | 26 ++++++++++++++++++++------
 include/linux/fs_context.h |  6 ++++++
 2 files changed, 26 insertions(+), 6 deletions(-)

diff --git a/fs/super.c b/fs/super.c
index 1db230432960..c9c7223bc2a2 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -1596,13 +1596,14 @@ int setup_bdev_super(struct super_block *sb, int sb_flags,
 EXPORT_SYMBOL_GPL(setup_bdev_super);
 
 /**
- * get_tree_bdev - Get a superblock based on a single block device
+ * get_tree_bdev_flags - Get a superblock based on a single block device
  * @fc: The filesystem context holding the parameters
  * @fill_super: Helper to initialise a new superblock
+ * @flags: GET_TREE_BDEV_* flags
  */
-int get_tree_bdev(struct fs_context *fc,
-		int (*fill_super)(struct super_block *,
-				  struct fs_context *))
+int get_tree_bdev_flags(struct fs_context *fc,
+		int (*fill_super)(struct super_block *sb,
+				  struct fs_context *fc), unsigned int flags)
 {
 	struct super_block *s;
 	int error = 0;
@@ -1613,10 +1614,10 @@ int get_tree_bdev(struct fs_context *fc,
 
 	error = lookup_bdev(fc->source, &dev);
 	if (error) {
-		errorf(fc, "%s: Can't lookup blockdev", fc->source);
+		if (!(flags & GET_TREE_BDEV_QUIET_LOOKUP))
+			errorf(fc, "%s: Can't lookup blockdev", fc->source);
 		return error;
 	}
-
 	fc->sb_flags |= SB_NOSEC;
 	s = sget_dev(fc, dev);
 	if (IS_ERR(s))
@@ -1644,6 +1645,19 @@ int get_tree_bdev(struct fs_context *fc,
 	fc->root = dget(s->s_root);
 	return 0;
 }
+EXPORT_SYMBOL_GPL(get_tree_bdev_flags);
+
+/**
+ * get_tree_bdev - Get a superblock based on a single block device
+ * @fc: The filesystem context holding the parameters
+ * @fill_super: Helper to initialise a new superblock
+ */
+int get_tree_bdev(struct fs_context *fc,
+		int (*fill_super)(struct super_block *,
+				  struct fs_context *))
+{
+	return get_tree_bdev_flags(fc, fill_super, 0);
+}
 EXPORT_SYMBOL(get_tree_bdev);
 
 static int test_bdev_super(struct super_block *s, void *data)
diff --git a/include/linux/fs_context.h b/include/linux/fs_context.h
index c13e99cbbf81..4b4bfef6f053 100644
--- a/include/linux/fs_context.h
+++ b/include/linux/fs_context.h
@@ -160,6 +160,12 @@ extern int get_tree_keyed(struct fs_context *fc,
 
 int setup_bdev_super(struct super_block *sb, int sb_flags,
 		struct fs_context *fc);
+
+#define GET_TREE_BDEV_QUIET_LOOKUP		0x0001
+int get_tree_bdev_flags(struct fs_context *fc,
+		int (*fill_super)(struct super_block *sb,
+				  struct fs_context *fc), unsigned int flags);
+
 extern int get_tree_bdev(struct fs_context *fc,
 			       int (*fill_super)(struct super_block *sb,
 						 struct fs_context *fc));
-- 
2.43.5