fs: add i_user_ns() helper

Since we'll be passing the filesystem's idmapping in even more places in
the following patches and we do already dereference struct inode to get
to the filesystem's idmapping multiple times add a tiny helper.

Link: https://lore.kernel.org/r/[email protected] (v1)
Link: https://lore.kernel.org/r/[email protected] (v2)
Link: https://lore.kernel.org/r/[email protected]
Cc: Seth Forshee <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Al Viro <[email protected]>
CC: [email protected]
Reviewed-by: Amir Goldstein <[email protected]>
Reviewed-by: Seth Forshee <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>

1 files changed, 9 insertions, 4 deletions

diff --git a/include/linux/fs.h b/include/linux/fs.h
index e1f28f757f1b..3d6d514943ab 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1600,6 +1600,11 @@ struct super_block {
 	struct list_head	s_inodes_wb;	/* writeback inodes */
 } __randomize_layout;
 
+static inline struct user_namespace *i_user_ns(const struct inode *inode)
+{
+	return inode->i_sb->s_user_ns;
+}
+
 /* Helper functions so that in most cases filesystems will
  * not need to deal directly with kuid_t and kgid_t and can
  * instead deal with the raw numeric values that are stored
@@ -1607,22 +1612,22 @@ struct super_block {
  */
 static inline uid_t i_uid_read(const struct inode *inode)
 {
-	return from_kuid(inode->i_sb->s_user_ns, inode->i_uid);
+	return from_kuid(i_user_ns(inode), inode->i_uid);
 }
 
 static inline gid_t i_gid_read(const struct inode *inode)
 {
-	return from_kgid(inode->i_sb->s_user_ns, inode->i_gid);
+	return from_kgid(i_user_ns(inode), inode->i_gid);
 }
 
 static inline void i_uid_write(struct inode *inode, uid_t uid)
 {
-	inode->i_uid = make_kuid(inode->i_sb->s_user_ns, uid);
+	inode->i_uid = make_kuid(i_user_ns(inode), uid);
 }
 
 static inline void i_gid_write(struct inode *inode, gid_t gid)
 {
-	inode->i_gid = make_kgid(inode->i_sb->s_user_ns, gid);
+	inode->i_gid = make_kgid(i_user_ns(inode), gid);
 }
 
 /**