CRED: Wrap task credential accesses in the XFS filesystem

Wrap access to task credentials so that they can be separated more easily from
the task_struct during the introduction of COW creds.

Change most current->(|e|s|fs)[ug]id to current_(|e|s|fs)[ug]id().

Change some task->e?[ug]id to task_e?[ug]id().  In some places it makes more
sense to use RCU directly rather than a convenient wrapper; these will be
addressed by later patches.
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: James Morris <jmorris@namei.org>
Acked-by: Serge Hallyn <serue@us.ibm.com>

fs/xfs/linux-2.6/xfs_ioctl.c

@@ -1006,7 +1006,7 @@ xfs_ioctl_setattr(
 	 * to the file owner ID, except in cases where the
 	 * CAP_FSETID capability is applicable.
 	 */
-	if (current->fsuid != ip->i_d.di_uid && !capable(CAP_FOWNER)) {
+	if (current_fsuid() != ip->i_d.di_uid && !capable(CAP_FOWNER)) {
 		code = XFS_ERROR(EPERM);
 		goto error_return;
 	}

fs/xfs/xfs_acl.c

@@ -366,7 +366,7 @@ xfs_acl_allow_set(
 		return ENOTDIR;
 	if (vp->i_sb->s_flags & MS_RDONLY)
 		return EROFS;
-	if (XFS_I(vp)->i_d.di_uid != current->fsuid && !capable(CAP_FOWNER))
+	if (XFS_I(vp)->i_d.di_uid != current_fsuid() && !capable(CAP_FOWNER))
 		return EPERM;
 	return 0;
 }
@@ -413,13 +413,13 @@ xfs_acl_access(
 		switch (fap->acl_entry[i].ae_tag) {
 		case ACL_USER_OBJ:
 			seen_userobj = 1;
-			if (fuid != current->fsuid)
+			if (fuid != current_fsuid())
 				continue;
 			matched.ae_tag = ACL_USER_OBJ;
 			matched.ae_perm = allows;
 			break;
 		case ACL_USER:
-			if (fap->acl_entry[i].ae_id != current->fsuid)
+			if (fap->acl_entry[i].ae_id != current_fsuid())
 				continue;
 			matched.ae_tag = ACL_USER;
 			matched.ae_perm = allows;