linux-kernel - Re: [PATCH v3 3/4] vsscanf(): do not skip spaces

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Message-ID: <546e2ab5-f520-c85e-d6f4-ca7b02457d4c@rasmusvillemoes.dk>
Date:   Mon, 12 Jun 2023 13:08:04 +0200
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Demi Marie Obenour <demi@...isiblethingslab.com>,
        Hans de Goede <hdegoede@...hat.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Juergen Gross <jgross@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
        Lee Jones <lee@...nel.org>, Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     linux-media@...r.kernel.org, linux-staging@...ts.linux.dev,
        linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v3 3/4] vsscanf(): do not skip spaces

On 10/06/2023 22.40, Demi Marie Obenour wrote:
> Passing spaces before e.g. an integer is usually
> not intended. 

Maybe, maybe not. But it's mandated by POSIX/C99.

And of course we are free to ignore that and implement our own semantics
(though within the constraints that we really want -Wformat to help us),
but there seems to be existing code in-tree that relies on this
behavior. For example I think this will break
fsl_sata_intr_coalescing_store() which uses a scanf format of "%u%u".

Sure, that could just say "%u %u" instead, but the point is that
currently it doesn't. So without some reasonably thorough analysis
across the tree, and updates of affected callers, NAK.

Rasmus