From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-fsdevel-owner@vger.kernel.org>
Received: from mx3-rdu2.redhat.com ([66.187.233.73]:51544 "EHLO mx1.redhat.com"
        rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP
        id S932366AbeGIJfs (ORCPT <rfc822;linux-fsdevel@vger.kernel.org>);
        Mon, 9 Jul 2018 05:35:48 -0400
From: David Howells <dhowells@redhat.com>
In-Reply-To: <10670.1531128774@warthog.procyon.org.uk>
References: <10670.1531128774@warthog.procyon.org.uk> <20180708210154.10423-4-ebiggers3@gmail.com> <20180708210154.10423-1-ebiggers3@gmail.com>
Cc: dhowells@redhat.com, Eric Biggers <ebiggers3@gmail.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        Eric Biggers <ebiggers@google.com>
Subject: Re: [PATCH 03/18] fs_context: fix detecting full log buffer
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-ID: <10921.1531128946.1@warthog.procyon.org.uk>
Date: Mon, 09 Jul 2018 10:35:46 +0100
Message-ID: <10922.1531128946@warthog.procyon.org.uk>
To: unlisted-recipients:; (no To-header on input)
Sender: linux-fsdevel-owner@vger.kernel.org
List-ID: <linux-fsdevel.vger.kernel.org>

David Howells <dhowells@redhat.com> wrote:

> > When 'head' and 'tail' wrap around, 'log->head - log->tail' will be
> > something like '4 - 252 = -248', and comparing that directly to the
> > array size is wrong.  Fix by casting to 'u8'.
> 
> I think a better fix is to use CIRC_CNT() or CIRC_SPACE().

Or it would be - if CIRC_CNT() and CIRC_SPACE() didn't leave a hole in the
buffer - but that's unnecessary if the head and tail counters can hold 2x the
ring size or more.

David