CRED: Wrap task credential accesses in the SYSV 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>
Cc: Christoph Hellwig <hch@infradead.org>
Signed-off-by: James Morris <jmorris@namei.org>

fs/sysv/ialloc.c

@@ -165,9 +165,9 @@ struct inode * sysv_new_inode(const struct inode * dir, mode_t mode)
 		if (S_ISDIR(mode))
 			mode |= S_ISGID;
 	} else
-		inode->i_gid = current->fsgid;
+		inode->i_gid = current_fsgid();
 
-	inode->i_uid = current->fsuid;
+	inode->i_uid = current_fsuid();
 	inode->i_ino = fs16_to_cpu(sbi, ino);
 	inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME_SEC;
 	inode->i_blocks = 0;