Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Organization: Red Hat UK Ltd. Registered Address: Red Hat UK Ltd, Amberley
        Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United
        Kingdom.
        Registered in England and Wales under Company Registration No. 3798903
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-kernel-owner@vger.kernel.org
Precedence: bulk

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