afs: Support interacting with multiple user namespaces

Modify struct afs_file_status to store owner as a kuid_t and group as
a kgid_t.

In xdr_decode_AFSFetchStatus as owner is now a kuid_t and group is now
a kgid_t don't use the EXTRACT macro. Instead perform the work of
the extract macro explicitly. Read the value with ntohl and
convert it to the appropriate type with make_kuid or make_kgid.
Test if the value is different from what is stored in status and
update changed. Update the value in status.

In xdr_encode_AFS_StoreStatus call from_kuid or from_kgid as
we are computing the on the wire encoding.

Initialize uids with GLOBAL_ROOT_UID instead of 0.
Initialize gids with GLOBAL_ROOT_GID instead of 0.

Cc: David Howells <[e-mail]>
Acked-by: Serge Hallyn <[e-mail]>
Signed-off-by: Eric W. Biederman <[e-mail]>

fs/afs/afs.h

···
 	u64			size;		/* file size */
 	afs_dataversion_t	data_version;	/* current data version */
 	u32			author;		/* author ID */
-	u32			owner;		/* owner ID */
-	u32			group;		/* group ID */
+	kuid_t			owner;		/* owner ID */
+	kgid_t			group;		/* group ID */
 	afs_access_t		caller_access;	/* access rights for authenticated caller */
 	afs_access_t		anon_access;	/* access rights for unauthenticated caller */
 	umode_t			mode;		/* UNIX mode */

fs/afs/fsclient.c

···
 	umode_t mode;
 	u64 data_version, size;
 	u32 changed = 0; /* becomes non-zero if ctime-type changes seen */
+	kuid_t owner;
+	kgid_t group;
 
 #define EXTRACT(DST)				\
 	do {					\
···
 	size = ntohl(*bp++);
 	data_version = ntohl(*bp++);
 	EXTRACT(status->author);
-	EXTRACT(status->owner);
+	owner = make_kuid(&init_user_ns, ntohl(*bp++));
+	changed |= !uid_eq(owner, status->owner);
+	status->owner = owner;
 	EXTRACT(status->caller_access); /* call ticket dependent */
 	EXTRACT(status->anon_access);
 	EXTRACT(status->mode);
···
 	bp++; /* seg size */
 	status->mtime_client = ntohl(*bp++);
 	status->mtime_server = ntohl(*bp++);
-	EXTRACT(status->group);
+	group = make_kgid(&init_user_ns, ntohl(*bp++));
+	changed |= !gid_eq(group, status->group);
+	status->group = group;
 	bp++; /* sync counter */
 	data_version |= (u64) ntohl(*bp++) << 32;
 	EXTRACT(status->lock_count);
···
 
 	if (attr->ia_valid & ATTR_UID) {
 		mask |= AFS_SET_OWNER;
-		owner = attr->ia_uid;
+		owner = from_kuid(&init_user_ns, attr->ia_uid);
 	}
 
 	if (attr->ia_valid & ATTR_GID) {
 		mask |= AFS_SET_GROUP;
-		group = attr->ia_gid;
+		group = from_kgid(&init_user_ns, attr->ia_gid);
 	}
 
 	if (attr->ia_valid & ATTR_MODE) {

fs/afs/inode.c

···
 
 	set_nlink(inode, vnode->status.nlink);
 	inode->i_uid		= vnode->status.owner;
-	inode->i_gid		= 0;
+	inode->i_gid		= GLOBAL_ROOT_GID;
 	inode->i_size		= vnode->status.size;
 	inode->i_ctime.tv_sec	= vnode->status.mtime_server;
 	inode->i_ctime.tv_nsec	= 0;
···
 	inode->i_mode		= S_IFDIR | S_IRUGO | S_IXUGO;
 	inode->i_op		= &afs_autocell_inode_operations;
 	set_nlink(inode, 2);
-	inode->i_uid		= 0;
-	inode->i_gid		= 0;
+	inode->i_uid		= GLOBAL_ROOT_UID;
+	inode->i_gid		= GLOBAL_ROOT_GID;
 	inode->i_ctime.tv_sec	= get_seconds();
 	inode->i_ctime.tv_nsec	= 0;
 	inode->i_atime		= inode->i_mtime = inode->i_ctime;

init/Kconfig

···
 	default y
 
 	# Filesystems
-	depends on AFS_FS = n
 	depends on CIFS = n
 	depends on CODA_FS = n
 	depends on GFS2_FS = n