[PATCH 2/8] fs: add two type safe mapping helpers

[Christian Brauner <brauner@kernel.org>]

Introduce i_{g,u}id_into_mnt{g,u}id(). They return kmnt{g,u}id_t. This
makes it way harder to confused idmapped mount {g,u}ids with filesystem
{g,u}ids.

The two helpers will eventually replace the old non type safe
i_{g,u}id_into_mnt() helpers once we finished converting all places. Add
a comment noting that they will be removed in the future.

All new helpers are nops on non-idmapped mounts.

Cc: Seth Forshee <sforshee@digitalocean.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Aleksa Sarai <cyphar@cyphar.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
CC: linux-fsdevel@vger.kernel.org
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
---
 include/linux/fs.h | 37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 9ad5e3520fae..8724a31b95e5 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1600,6 +1600,9 @@ static inline void i_gid_write(struct inode *inode, gid_t gid)
  * @mnt_userns: user namespace of the mount the inode was found from
  * @inode: inode to map
  *
+ * Note, this will eventually be removed completely in favor of the type-safe
+ * i_uid_into_mntuid().
+ *
  * Return: the inode's i_uid mapped down according to @mnt_userns.
  * If the inode's i_uid has no mapping INVALID_UID is returned.
  */
@@ -1609,11 +1612,28 @@ static inline kuid_t i_uid_into_mnt(struct user_namespace *mnt_userns,
 	return mapped_kuid_fs(mnt_userns, i_user_ns(inode), inode->i_uid);
 }
 
+/**
+ * i_uid_into_mntuid - map an inode's i_uid down into a mnt_userns
+ * @mnt_userns: user namespace of the mount the inode was found from
+ * @inode: inode to map
+ *
+ * Return: whe inode's i_uid mapped down according to @mnt_userns.
+ * If the inode's i_uid has no mapping INVALID_KMNTUID is returned.
+ */
+static inline kmntuid_t i_uid_into_mntuid(struct user_namespace *mnt_userns,
+					  const struct inode *inode)
+{
+	return KMNTUIDT_INIT(i_uid_into_mnt(mnt_userns, inode));
+}
+
 /**
  * i_gid_into_mnt - map an inode's i_gid down into a mnt_userns
  * @mnt_userns: user namespace of the mount the inode was found from
  * @inode: inode to map
  *
+ * Note, this will eventually be removed completely in favor of the type-safe
+ * i_gid_into_mntgid().
+ *
  * Return: the inode's i_gid mapped down according to @mnt_userns.
  * If the inode's i_gid has no mapping INVALID_GID is returned.
  */
@@ -1623,6 +1643,23 @@ static inline kgid_t i_gid_into_mnt(struct user_namespace *mnt_userns,
 	return mapped_kgid_fs(mnt_userns, i_user_ns(inode), inode->i_gid);
 }
 
+/**
+ * i_gid_into_mnt - map an inode's i_gid down into a mnt_userns
+ * @mnt_userns: user namespace of the mount the inode was found from
+ * @inode: inode to map
+ *
+ * Note, this will eventually be removed completely in favor of the type-safe
+ * i_gid_into_mntgid().
+ *
+ * Return: the inode's i_gid mapped down according to @mnt_userns.
+ * If the inode's i_gid has no mapping INVALID_KMNTGID is returned.
+ */
+static inline kmntgid_t i_gid_into_mntgid(struct user_namespace *mnt_userns,
+					  const struct inode *inode)
+{
+	return KMNTGIDT_INIT(i_gid_into_mnt(mnt_userns, inode));
+}
+
 /**
  * inode_fsuid_set - initialize inode's i_uid field with callers fsuid
  * @inode: inode to initialize
-- 
2.34.1