Re: [alsa-devel] [PATCH] ALSA: uapi: Replace __packed with __attribute__((packed))

[Takashi Iwai <tiwai@suse.de>]

On Fri, 07 Feb 2020 17:02:27 +0100,
Amadeusz SX2awiX4ski wrote:
> 
> On 2/7/2020 4:17 PM, Takashi Iwai wrote:
> > On Fri, 07 Feb 2020 17:15:33 +0100,
> > Amadeusz Sławiński wrote:
> >>
> >> Userspace doesn't know what __packed is, change it to
> >> __attribute__((packed)), like in the rest of a header.
> >>
> >> Fixes: 348f48220b97 (ASoC: topology: Move v4 manifest header data structures to uapi)
> >>
> >> Signed-off-by: Amadeusz Sławiński <amadeuszx.slawinski@linux.intel.com>
> >
> > Is it a general consensus that we have to replace that?
> 
> Well, it aligns the packed structs definition with the rest of the
> file and the program I tried compiling built fine after this
> adjustment.

It's a different reason from "userspace doesn't know what __packed is"
:)

I'm not against the change, but rather wondering about the rationale
behind the changes.

> As I understand, uapi files are usually installed by
> scripts/headers_install.pl, which takes care of replacing __packed
> with __attribute((packed)). However if I do 'make install' in alsa-lib
> it seems to install this one header containing __packed.

This was rather an oversight and we should have converted at copying
over the alsa-lib repo.  It's not an issue in the kernel header, per
se.


thanks,

Takashi

> In theory alsa-lib also installs /usr/include/alsa/sound/type_compat.h
> but to me it seems more like a workaround if I can have working header
> without additional includes.
> Also while there is a few more headers in kernel with __packed, this
> one is the only one included in alsa-lib and being installed by it:
> 
> $ pwd
> .../alsa-lib
> $ grep -RI __packed *
> include/sound/type_compat.h:#ifndef __packed
> include/sound/type_compat.h:#define __packed __attribute__((packed))
> include/sound/uapi/asoc.h:} __packed;
> include/sound/uapi/asoc.h:} __packed;
> include/sound/uapi/asoc.h:} __packed;
> include/sound/uapi/asoc.h:} __packed;
> $ pwd
> .../linux
> $ grep -RI __packed include/uapi/sound
> include/uapi/sound/asoc.h:} __packed;
> include/uapi/sound/asoc.h:} __packed;
> include/uapi/sound/asoc.h:} __packed;
> include/uapi/sound/asoc.h:} __packed;
> include/uapi/sound/sof/fw.h:} __packed;
> include/uapi/sound/sof/fw.h:} __packed;
> include/uapi/sound/sof/fw.h:} __packed;
> include/uapi/sound/sof/header.h:}  __packed;
> include/uapi/sound/skl-tplg-interface.h:} __packed;
> include/uapi/sound/skl-tplg-interface.h:} __packed;
> include/uapi/sound/skl-tplg-interface.h:} __packed;
> include/uapi/sound/skl-tplg-interface.h:} __packed;
> include/uapi/sound/skl-tplg-interface.h:} __packed;
> include/uapi/sound/skl-tplg-interface.h:} __packed;
> $ grep -RI __packed include/uapi/sound | wc -l
> 14
> $ grep -RI __attribute__\(\(packed include/uapi/sound | wc -l
> 40
> 
> I would say it is better to be consistent.
> 
> > Userspace doesn't know of __u16 unless it's defined, either, for
> > example.
> 
> The header itself has <linux/types.h> include which seems to be enough
> to take care of integer type definitions.
> 
> Amadeusz
> 
> >
> > thanks,
> >
> > Takashi
> >
> >> ---
> >>   include/uapi/sound/asoc.h | 8 ++++----
> >>   1 file changed, 4 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/include/uapi/sound/asoc.h b/include/uapi/sound/asoc.h
> >> index 6048553c119d..1ae8b06691cb 100644
> >> --- a/include/uapi/sound/asoc.h
> >> +++ b/include/uapi/sound/asoc.h
> >> @@ -586,7 +586,7 @@ struct snd_soc_tplg_manifest_v4 {
> >>   	__le32 pcm_elems;	/* number of PCM elements */
> >>   	__le32 dai_link_elems;	/* number of DAI link elements */
> >>   	struct snd_soc_tplg_private priv;
> >> -} __packed;
> >> +} __attribute((packed));
> >>     /* Stream Capabilities v4 */
> >>   struct snd_soc_tplg_stream_caps_v4 {
> >> @@ -604,7 +604,7 @@ struct snd_soc_tplg_stream_caps_v4 {
> >>   	__le32 period_size_max;	/* max period size bytes */
> >>   	__le32 buffer_size_min;	/* min buffer size bytes */
> >>   	__le32 buffer_size_max;	/* max buffer size bytes */
> >> -} __packed;
> >> +} __attribute((packed));
> >>     /* PCM v4 */
> >>   struct snd_soc_tplg_pcm_v4 {
> >> @@ -619,7 +619,7 @@ struct snd_soc_tplg_pcm_v4 {
> >>   	struct snd_soc_tplg_stream stream[SND_SOC_TPLG_STREAM_CONFIG_MAX]; /* for DAI link */
> >>   	__le32 num_streams;	/* number of streams */
> >>   	struct snd_soc_tplg_stream_caps_v4 caps[2]; /* playback and capture for DAI */
> >> -} __packed;
> >> +} __attribute((packed));
> >>     /* Physical link config v4 */
> >>   struct snd_soc_tplg_link_config_v4 {
> >> @@ -627,6 +627,6 @@ struct snd_soc_tplg_link_config_v4 {
> >>   	__le32 id;              /* unique ID - used to match */
> >>   	struct snd_soc_tplg_stream stream[SND_SOC_TPLG_STREAM_CONFIG_MAX]; /* supported configs playback and captrure */
> >>   	__le32 num_streams;     /* number of streams */
> >> -} __packed;
> >> +} __attribute((packed));
> >>     #endif
> >> -- 
> >> 2.17.1
> >>
> > _______________________________________________
> > Alsa-devel mailing list
> > Alsa-devel@alsa-project.org
> > https://mailman.alsa-project.org/mailman/listinfo/alsa-devel
> >
> 
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