linux-kernel - Re: [PATCH 8/8] ALSA: add new 32-bit layout for snd_pcm_mmap

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Date:   Thu, 26 Apr 2018 17:14:59 +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>,
        Mark Brown <broonie@...nel.org>,
        Takashi Sakamoto <o-takashi@...amocchi.jp>,
        Ingo Molnar <mingo@...nel.org>,
        SF Markus Elfring <elfring@...rs.sourceforge.net>,
        Dan Carpenter <dan.carpenter@...cle.com>, jeeja.kp@...el.com,
        Vinod Koul <vinod.koul@...el.com>,
        Guneshwor Singh <guneshwor.o.singh@...el.com>,
        subhransu.s.prusty@...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>,
        Fabian Frederick <fabf@...net.be>, alsa-devel@...a-project.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 8/8] ALSA: add new 32-bit layout for snd_pcm_mmap_status/control

On Tue, Apr 24, 2018 at 2:06 PM, Baolin Wang <baolin.wang@...aro.org> wrote:

> -struct snd_pcm_mmap_status {
> +/*
> + * For mmap operations, we need the 64-bit layout, both for compat mode,
> + * and for y2038 compatibility. For 64-bit applications, the two definitions
> + * are identical, so we keep the traditional version.
> + */
> +#ifdef __SND_STRUCT_TIME64
> +#define __snd_pcm_mmap_status64                snd_pcm_mmap_status
> +#define __snd_pcm_mmap_control64       snd_pcm_mmap_control
> +#define __snd_pcm_sync_ptr64           snd_pcm_sync_ptr
> +#else
> +#define __snd_pcm_mmap_status          snd_pcm_mmap_status
> +#define __snd_pcm_mmap_control         snd_pcm_mmap_control
> +#define __snd_pcm_sync_ptr             snd_pcm_sync_ptr
> +#endif
> +
> +struct __snd_pcm_mmap_status {
>         snd_pcm_state_t state;          /* RO: state - SNDRV_PCM_STATE_XXXX */
>         int pad1;                       /* Needed for 64 bit alignment */
>         snd_pcm_uframes_t hw_ptr;       /* RO: hw ptr (0...boundary-1) */

One more thing here: this definition is slightly suboptimal because in
an alsa-lib that gets built with 64-bit time_t, we end up with an unusable
__snd_pcm_mmap_status structure (__snd_pcm_mmap_status64 works
fine, and that would be the normal thing to use). Just in case we want
to be able to build an alsa-lib that is capable of running both on
new kernels with 64-bit time_t interfaces exposed to applications and
also on old kernels that don't have the new ioctls, we probably want
another fixup merged in:

diff --git a/include/uapi/sound/asound.h b/include/uapi/sound/asound.h
index 18fbdcb2c7b6..638c717d3eb9 100644
--- a/include/uapi/sound/asound.h
+++ b/include/uapi/sound/asound.h
@@ -496,19 +496,30 @@ struct snd_pcm_status {
 #define __snd_pcm_mmap_status64                snd_pcm_mmap_status
 #define __snd_pcm_mmap_control64       snd_pcm_mmap_control
 #define __snd_pcm_sync_ptr64           snd_pcm_sync_ptr
+#define __snd_timespec64               timespec
+struct __snd_timespec {
+       __s32 tv_sec;
+       __s32 tv_nsec;
+};
 #else
 #define __snd_pcm_mmap_status          snd_pcm_mmap_status
 #define __snd_pcm_mmap_control         snd_pcm_mmap_control
 #define __snd_pcm_sync_ptr             snd_pcm_sync_ptr
+#define __snd_timespec                 timespec
+struct __snd_timespec64 {
+       __s64 tv_sec;
+       __s64 tv_nsec;
+};
+
 #endif

 struct __snd_pcm_mmap_status {
        snd_pcm_state_t state;          /* RO: state - SNDRV_PCM_STATE_XXXX */
        int pad1;                       /* Needed for 64 bit alignment */
        snd_pcm_uframes_t hw_ptr;       /* RO: hw ptr (0...boundary-1) */
-       struct timespec tstamp;         /* Timestamp */
+       struct __snd_timespec tstamp;   /* Timestamp */
        snd_pcm_state_t suspended_state; /* RO: suspended stream state */
-       struct timespec audio_tstamp;   /* from sample counter or wall clock */
+       struct __snd_timespec audio_tstamp; /* from sample counter or
wall clock */
 };

 struct __snd_pcm_mmap_control {
@@ -532,11 +543,6 @@ struct __snd_pcm_sync_ptr {
        } c;
 };

-struct __snd_timespec64 {
-       __s64 tv_sec;
-       __s64 tv_nsec;
-};
-
 #if defined(__BYTE_ORDER) ? __BYTE_ORDER == __BIG_ENDIAN :
defined(__BIG_ENDIAN)
 typedef char __pad_before_uframe[sizeof(__u64) - sizeof(snd_pcm_uframes_t)];
 typedef char __pad_after_uframe[0];

With this change, alsa-lib can either access whichever structure
matches the glibc 'timespec' definition, or it can ask for
__struct __snd_pcm_mmap_status and struct __snd_pcm_mmap_status64
explicitly, regardless of the time_t definition.

         Arnd