fs: Create sb_same_encoding() helper

For cases where a file lookup can look in different filesystems (like in
overlayfs), both super blocks must have the same encoding and the same
flags. To help with that, create a sb_same_encoding() function.

Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: André Almeida <andrealmeid@igalia.com>
Reviewed-by: Gabriel Krisman Bertazi <gabriel@krisman.be>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>

1 files changed, 18 insertions, 0 deletions

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 43b3a7cf6750..ec867f112fd5 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3754,6 +3754,24 @@ static inline bool sb_has_encoding(const struct super_block *sb)
 	return !!sb_encoding(sb);
 }
 
+/*
+ * Compare if two super blocks have the same encoding and flags
+ */
+static inline bool sb_same_encoding(const struct super_block *sb1,
+				    const struct super_block *sb2)
+{
+#if IS_ENABLED(CONFIG_UNICODE)
+	if (sb1->s_encoding == sb2->s_encoding)
+		return true;
+
+	return (sb1->s_encoding && sb2->s_encoding &&
+	       (sb1->s_encoding->version == sb2->s_encoding->version) &&
+	       (sb1->s_encoding_flags == sb2->s_encoding_flags));
+#else
+	return true;
+#endif
+}
+
 int may_setattr(struct mnt_idmap *idmap, struct inode *inode,
 		unsigned int ia_valid);
 int setattr_prepare(struct mnt_idmap *, struct dentry *, struct iattr *);