Add ia_mnt{g,u}id members of type kmnt{g,u}id_t to struct iattr. We use
an anonymous union (similar to what we do in struct file) around
ia_{g,u}id and ia_mnt{g,u}id.
At the end of this series ia_{g,u}id and ia_mnt{g,u}id will always
contain the same value independent of whether struct iattr is
initialized from an idmapped mount. This is a change from how this is
done today.
Wrapping this in a anonymous unions has a few advantages. It allows us
to avoid needlessly increasing struct iattr. Since the types for
ia_{g,u}id and ia_mnt{g,u}id are structures with overlapping/identical
members they are covered by 6.5.2.3/6 of the C standard and it is safe
to initialize and access them.
Filesystems that raise FS_ALLOW_IDMAP and thus support idmapped mounts
will have to use ia_mnt{g,u}id and the associated helpers. And will be
ported at the end of this series. They will immediately benefit from the
type safe new helpers.
Filesystems that do not support FS_ALLOW_IDMAP can continue to use
ia_{g,u}id for now. The aim is to convert every filesystem to always use
ia_mnt{g,u}id and thus ultimately remove the ia_{g,u}id members.
Cc: Seth Forshee <sforshee@xxxxxxxxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Aleksa Sarai <cyphar@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
CC: linux-fsdevel@xxxxxxxxxxxxxxx
Signed-off-by: Christian Brauner (Microsoft) <brauner@xxxxxxxxxx>
---
include/linux/fs.h | 18 ++++++++++++++++--
include/linux/mnt_idmapping.h | 5 +++++
2 files changed, 21 insertions(+), 2 deletions(-)
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 8724a31b95e5..0da6c0481dbd 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -221,8 +221,22 @@ typedef int (dio_iodone_t)(struct kiocb *iocb, loff_t offset,
struct iattr {
unsigned int ia_valid;
umode_t ia_mode;
- kuid_t ia_uid;
- kgid_t ia_gid;
+ /*
+ * The two anonymous unions wrap structures with the same member.
+ *
+ * Filesystems raising FS_ALLOW_IDMAP need to use ia_mnt{g,u}id which
+ * are a dedicated type requiring the filesystem to use the dedicated
+ * helpers. Other filesystem can continue to use ia_{g,u}id until they
+ * have been ported.
+ */
+ union {
+ kuid_t ia_uid;
+ kmntuid_t ia_mntuid;
+ };
+ union {
+ kgid_t ia_gid;
+ kmntgid_t ia_mntgid;
+ };
loff_t ia_size;
struct timespec64 ia_atime;
struct timespec64 ia_mtime;
diff --git a/include/linux/mnt_idmapping.h b/include/linux/mnt_idmapping.h
index 8dbaef494e02..8f555c746cf4 100644
--- a/include/linux/mnt_idmapping.h
+++ b/include/linux/mnt_idmapping.h
@@ -21,6 +21,11 @@ typedef struct {
gid_t val;
} kmntgid_t;
+static_assert(sizeof(kmntuid_t) == sizeof(kuid_t));
+static_assert(sizeof(kmntgid_t) == sizeof(kgid_t));
+static_assert(offsetof(kmntuid_t, val) == offsetof(kuid_t, val));
+static_assert(offsetof(kmntgid_t, val) == offsetof(kgid_t, val));
+
#ifdef CONFIG_MULTIUSER
static inline uid_t __kmntuid_val(kmntuid_t uid)
{
--
2.34.1
