linux-kernel - Re: [RFC PATCH 4/7] sound: core: Avoid using timespec for struct snd_rawmidi

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Date:   Thu, 21 Sep 2017 14:56:48 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Baolin Wang <baolin.wang@...aro.org>
Cc:     Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Ingo Molnar <mingo@...nel.org>,
        Takashi Sakamoto <o-takashi@...amocchi.jp>,
        SF Markus Elfring <elfring@...rs.sourceforge.net>,
        Dan Carpenter <dan.carpenter@...cle.com>, jeeja.kp@...el.com,
        Vinod Koul <vinod.koul@...el.com>, dharageswari.r@...el.com,
        guneshwor.o.singh@...el.com, Bhumika Goyal <bhumirks@...il.com>,
        gudishax.kranthikumar@...el.com, Naveen M <naveen.m@...el.com>,
        hardik.t.shah@...el.com, Arvind Yadav <arvind.yadav.cs@...il.com>,
        fabf@...net.be, Mark Brown <broonie@...nel.org>,
        Deepa Dinamani <deepa.kernel@...il.com>,
        alsa-devel@...a-project.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 4/7] sound: core: Avoid using timespec for struct snd_rawmidi_status

On Thu, Sep 21, 2017 at 8:18 AM, Baolin Wang <baolin.wang@...aro.org> wrote:

> -       case SNDRV_RAWMIDI_IOCTL_STATUS:
> +#if __BITS_PER_LONG == 32
> +       case SNDRV_RAWMIDI_IOCTL_STATUS32:
> +       {
> +               int err = 0;
> +               struct snd_rawmidi_status32 __user *status = argp;
> +               struct snd_rawmidi_status32 status32;
> +               struct snd_rawmidi_status64 status64;
> +
> +               if (copy_from_user(&status32, argp,
> +                                  sizeof(struct snd_rawmidi_status32)))
> +                       return -EFAULT;
> +               switch (status32.stream) {
> +               case SNDRV_RAWMIDI_STREAM_OUTPUT:
> +                       if (rfile->output == NULL)
> +                               return -EINVAL;
> +                       err = snd_rawmidi_output_status(rfile->output, &status64);
> +                       break;
> +               case SNDRV_RAWMIDI_STREAM_INPUT:
> +                       if (rfile->input == NULL)
> +                               return -EINVAL;
> +                       err = snd_rawmidi_input_status(rfile->input, &status64);
> +                       break;
> +               default:
> +                       return -EINVAL;
> +               }
> +               if (err < 0)
> +                       return err;
> +
> +               if (put_user(status64.stream, &status->stream) ||
> +                   put_user(status64.tstamp.tv_sec, &status->tstamp.tv_sec) ||
> +                   put_user(status64.tstamp.tv_nsec, &status->tstamp.tv_nsec) ||
> +                   put_user(status64.avail, &status->avail) ||
> +                   put_user(status64.xruns, &status->xruns))
> +                       return -EFAULT;
> +               return 0;
> +       }

This follows the existing coding style for the other functions, but I think
it would be nicer to express the last part as

       status32 = (struct snd_rawmidi_status32) {
               .stream = status->stream,
               .tstamp.tv_sec, &status->tstamp.tv_sec,
               .tstamp.tv_nsec, &status->tstamp.tv_nsec,
               .avail, &status->avail,
               .xruns, &status->xruns,
       };
       if (copy_to_user(status, &status32, sizeof(*status))
              return -EFAULT;
       return 0;

It's completely equivalent, I just find my version easier to read, and
it should produce slightly better object code.

Maybe the maintainers have a preference, or there might be
a good reason to use the series of put_user() instead.

       Arnd