CRED: Use creds in file structs

Attach creds to file structs and discard f_uid/f_gid.

file_operations::open() methods (such as hppfs_open()) should use file->f_cred
rather than current_cred().  At the moment file->f_cred will be current_cred()
at this point.

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: James Morris <jmorris@namei.org>
Signed-off-by: James Morris <jmorris@namei.org>
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 3bfec13..c0fb6d8 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -827,7 +827,7 @@
 	fmode_t			f_mode;
 	loff_t			f_pos;
 	struct fown_struct	f_owner;
-	unsigned int		f_uid, f_gid;
+	const struct cred	*f_cred;
 	struct file_ra_state	f_ra;
 
 	u64			f_version;