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

[Amadeusz Sławiński]

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 at 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.

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.
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
>>
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