linux-kernel - Re: [RFC PATCH 04/10] pipe: Use head and tail pointers for the ring, not cursor and length [ver #2]

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Message-ID: <16620.1572534687@warthog.procyon.org.uk>
Date:   Thu, 31 Oct 2019 15:11:27 +0000
From:   David Howells <dhowells@...hat.com>
To:     Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:     dhowells@...hat.com, Ilya Dryomov <idryomov@...il.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        nicolas.dichtel@...nd.com, raven@...maw.net,
        Christian Brauner <christian@...uner.io>,
        keyrings@...r.kernel.org, linux-usb@...r.kernel.org,
        linux-block <linux-block@...r.kernel.org>,
        linux-security-module@...r.kernel.org,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-api@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 04/10] pipe: Use head and tail pointers for the ring, not cursor and length [ver #2]

How about:

 * We use head and tail indices that aren't masked off, except at the
 * point of dereference, but rather they're allowed to wrap naturally.
 * This means there isn't a dead spot in the buffer, provided the ring
 * size is a power of two and <= 2^31.

David