Message-ID: <s5hk1847rvm.wl-tiwai@suse.de>
Date:   Tue, 12 Nov 2019 21:37:49 +0100
From:   Takashi Iwai <tiwai@...e.de>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     <alsa-devel@...a-project.org>, Takashi Iwai <tiwai@...e.com>,
        Baolin Wang <baolin.wang7@...il.com>, <y2038@...ts.linaro.org>,
        <linux-kernel@...r.kernel.org>, Jaroslav Kysela <perex@...ex.cz>,
        Mark Brown <broonie@...nel.org>
Subject: Re: [PATCH v6 0/8] Fix year 2038 issue for sound subsystem

On Tue, 12 Nov 2019 16:16:34 +0100,
Arnd Bergmann wrote:
> 
> This is a series I worked on with Baolin in 2017 and 2018, but we
> never quite managed to finish up the last pieces. During the
> ALSA developer meetup at ELC-E 2018 in Edinburgh, a decision was
> made to go with this approach for keeping best compatibility
> with existing source code, and then I failed to follow up by
> resending the patches.
> 
> Now I have patches for all remaining time_t uses in the kernel,
> so it's absolutely time to revisit them. I have done more
> review of the patches myself and found a couple of minor issues
> that I have fixed up, otherwise the series is still the same as
> before.
> 
> Conceptually, the idea of these patches is:
> 
> - 64-bit applications should see no changes at all, neither
>   compile-time nor run-time.
> 
> - 32-bit code compiled with a 64-bit time_t currently
>   does not work with ALSA, and requires kernel changes and/or
>   sound/asound.h changes
> 
> - Most 32-bit code using these interfaces will work correctly
>   on a modified kernel, with or without the uapi header changes.
> 
> - 32-bit code using SNDRV_TIMER_IOCTL_TREAD requires the
>   updated header file for 64-bit time_t support
> 
> - 32-bit i386 user space with 64-bit time_t is broken for
>   SNDRV_PCM_IOCTL_STATUS, SNDRV_RAWMIDI_IOCTL_STATUS and
>   SNDRV_PCM_IOCTL_SYNC_PTR because of i386 alignment. This is also
>   addressed by the updated uapi header.
> 
> - PCM mmap is currently supported on native x86 kernels
>   (both 32-bit and 64-bit) but not for compat mode. This series breaks
>   the 32-bit native mmap support for 32-bit time_t, but instead allows
>   it for 64-bit time_t on both native and compat kernels. This seems to
>   be the best trade-off, as mmap support is optional already, and most
>   32-bit code runs in compat mode anyway.
> 
> - I've tried to avoid breaking compilation of 32-bit code
>   as much as possible. Anything that does break however is likely code
>   that is already broken on 64-bit time_t and needs source changes to
>   fix them.
> 
> I would like to propose merging this into the alsa tree after
> the v5.5 merge window for inclusion into v5.6, to allow a good
> amount of testing, in particular for the header changes that
> may cause problems for user space applications.

Agreed, it's still no urgent problem.

> A git branch with the same contents is available for testing at [1].
> 
> Please review and test!
> 
>      Arnd

So now taking a quick look through the series, I find this approach is
the way to go.  Although one might get a bit more optimization after
squeeze, it's already a good compromise between the readability and
the efficiency.

A slight uncertain implementation is the timer tread stuff, especially
the conditional definition of SNDRV_TIMER_IOCTL_TREAD (IIRC, I already
complained it in the past, too).  But I have no other idea as well, so
unless someone else gives a better option, we can live with that.


Thanks!

Takashi

> 
> [1] https://git.kernel.org/pub/scm/linux/kernel/git/arnd/playground.git y2038-alsa
> [2] https://lore.kernel.org/lkml/CAK8P3a2Os66+iwQYf97qh05W2JP8rmWao8zmKoHiXqVHvyYAJA@mail.gmail.com/T/#m6519cb07cfda08adf1dedea6596bb98892b4d5dc
> 
> Changes since v5 (Arnd):
>  - Rebased to linux-5.4-rc4
>  - Updated to completely remove timespec and time_t references from alsa
>  - found and fixed a few bugs
> 
> Changes since v4 (Baolin):
>  - Add patch 5 to change trigger_tstamp member of struct snd_pcm_runtime.
>  - Add patch 8 to change internal timespec.
>  - Add more explanation in commit message.
>  - Use ktime_get_real_ts64() in patch 6.
>  - Split common code out into a separate function in patch 6.
>  - Fix tu->tread bug in patch 6 and remove #if __BITS_PER_LONG == 64 macro.
> 
> Changes since v3:
>  - Move struct snd_pcm_status32 to pcm.h file.
>  - Modify comments and commit message.
>  - Add new patch2 ~ patch6.
> 
> Changes since v2:
>  - Renamed all structures to make clear.
>  - Remove CONFIG_X86_X32 macro and introduced new compat_snd_pcm_status64_x86_32.
> 
> Changes since v1:
>  - Add one macro for struct snd_pcm_status_32 which only active in 32bits kernel.
>  - Convert pcm_compat.c to use struct snd_pcm_status_64.
>  - Convert pcm_native.c to use struct snd_pcm_status_64.
> 
> ---
> 
> Arnd Bergmann (2):
>   ALSA: move snd_pcm_ioctl_sync_ptr_compat into pcm_native.c
>   ALSA: add new 32-bit layout for snd_pcm_mmap_status/control
> 
> Baolin Wang (6):
>   ALSA: Replace timespec with timespec64
>   ALSA: Avoid using timespec for struct snd_timer_status
>   ALSA: Avoid using timespec for struct snd_ctl_elem_value
>   ALSA: Avoid using timespec for struct snd_pcm_status
>   ALSA: Avoid using timespec for struct snd_rawmidi_status
>   ALSA: Avoid using timespec for struct snd_timer_tread
> 
>  include/sound/pcm.h               |  74 ++++++--
>  include/sound/timer.h             |   4 +-
>  include/uapi/sound/asound.h       | 132 ++++++++++++--
>  sound/core/pcm.c                  |  12 +-
>  sound/core/pcm_compat.c           | 282 ++++++++----------------------
>  sound/core/pcm_lib.c              |  38 ++--
>  sound/core/pcm_native.c           | 226 +++++++++++++++++++++---
>  sound/core/rawmidi.c              | 132 +++++++++++---
>  sound/core/rawmidi_compat.c       |  87 +++------
>  sound/core/timer.c                | 229 ++++++++++++++++++------
>  sound/core/timer_compat.c         |  62 +------
>  sound/pci/hda/hda_controller.c    |  10 +-
>  sound/soc/intel/skylake/skl-pcm.c |   4 +-
>  13 files changed, 804 insertions(+), 488 deletions(-)
> 
> -- 
> 2.20.0
> 

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