linux-kernel - Re: [BACKPORT 4.4.y 02/25] ALSA: compress: add support for 32bit calls in a 64bit kernel

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Message-ID: <CAK8P3a22Mp9yR49CEe2bq240SuSpbvy1XBDa2sSvWYMt=AZM3Q@mail.gmail.com>
Date:   Tue, 26 Mar 2019 08:55:14 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     "# 3.4.x" <stable@...r.kernel.org>, Vinod Koul <vkoul@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Ravindra Lokhande <rlokhande@...dia.com>,
        Vinod Koul <vinod.koul@...el.com>,
        Takashi Iwai <tiwai@...e.de>, Mark Brown <broonie@...nel.org>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Joe Perches <joe@...ches.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        ALSA Development Mailing List <alsa-devel@...a-project.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [BACKPORT 4.4.y 02/25] ALSA: compress: add support for 32bit
 calls in a 64bit kernel

On Tue, Mar 26, 2019 at 2:23 AM Greg KH <gregkh@...uxfoundation.org> wrote:
>
> On Fri, Mar 22, 2019 at 04:43:53PM +0100, Arnd Bergmann wrote:
> > From: Ravindra Lokhande <rlokhande@...dia.com>
> >
> > Compress offload does not support ioctl calls from a 32bit userspace
> > in a 64 bit kernel. This patch adds support for ioctls from a 32bit
> > userspace in a 64bit kernel
> >
> > Signed-off-by: Ravindra Lokhande <rlokhande@...dia.com>
> > Acked-by: Vinod Koul <vinod.koul@...el.com>
> > Signed-off-by: Takashi Iwai <tiwai@...e.de>
> > (cherry picked from commit c10368897e104c008c610915a218f0fe5fa4ec96)
> > Signed-off-by: Arnd Bergmann <arnd@...db.de>
> > ---
> >  sound/core/compress_offload.c | 13 +++++++++++++
> >  1 file changed, 13 insertions(+)
>
> How is this not a "new feature"?  What bug does this fix?  Has this ever
> worked in the past?

It has never worked in the past, but I consider it a bug for the compat layer
to behave differently from native code. In this case, any 32-bit application
using the SNDRV_COMPRESS_* ioctls will just fail to do anything on
a 64-bit kernel at all without the trivial fix that should have been there when
the driver was originally merged.

     Arnd