[alsa-devel] [PATCH] Emit an error message when dlopen fails.

[Jaroslav Kysela]

Dne 22.11.2017 v 10:30 Takashi Sakamoto napsal(a):
> On Nov 22 2017 16:45, Cedric Roux wrote:
>> Ah, this is a problem.
>> But I struggled with the "alsaeq plugin" which, under ubuntu 17 something
>> is not linked against libasound and when pulseaudio is configured to use
>> it, it fails without saying anything useful and the hacker (me) has to spend too
>> much time because ALSA does not use dlerror.
>>
>>>
>>> (parsing alsa.conf)
>>> snd_config_hooks_call()
>>>    ->snd_dlopen(name = NULL)
>>>      if (name == NULL)
>>>        name = self
>>>      filename = ALSA_PLUGIN_DIR + '/' + name
>>>      dlopen(filename)
>>>      (generate the error messages)
>>>
>>> I don't know why alsa-lib is programmed as what it is, so have no idea to suggest better solution...
>>>
>>> Additionally, your patch includes some issues of patch format:
>>> * Not only your signature but also patch comment is required. The first
>>>    line is interpreted as patch title, and the rest is as comment.
>>
>> okay, next time I'll write some text.
>>
>>> * Patches should be compliant to git-patch format. I encountered failure
>>>    of 'git am' for this patch. Please use 'git format-patch' command to
>>>    generate patches for posting.
>>
>> I used format-patch and imap-send. Maybe this bloated thunderbird did
>> mess up (I configured it as explained in the man pages).
> 
> Aha. You did use git-format-patch to generate it.
> 
> When I generate patches by 'git format-patch', code differences are 
> output with 'diff --git a/src/dlmisc.c b/src/dlmisc.c'. On the other 
> hand, your patch includes 'diff --git src/dlmisc.c src/dlmisc.c'. As 
> long as asking my colleague, this seems to come from '--no-prefix' 
> option for 'git-format-patch'. This is a cause of my failure to run 'git 
> am' because an additional option, '-p1' is required to apply your patch. 
> Now I got it.
> 
>> Anyway, do what you want with the patch above, I don't really care actually.
>> Problem is solved on my side. I've seen messages in the wild from people
>> with the same problem, I thought I could help a bit. I didn't see the
>> "big picture" (that is: bad design of too many software).
>>
>> All I know is that it's good practice to report errors to users. If
>> a code path can "legitimately" generate errors, then the programmer
>> needs to deal with it in a convenient way.
>>
>> But yeah, I don't care. ALSA lib is bloated to start with.
>> (This email is my last, I won't troll more, promise.)
> 
> Current implementation of alsa-lib is too bloated to me as well. But I'd 
> like to avoid people encountering the similar issues. This is my 
> motivation to tackle such a huge, complicated and troublesome library.

We should return the error string from snd_dlopen() in this case. It's
up to the caller to handle this (ignore or print) correctly.

I will implement it.

						Jaroslav

-- 
Jaroslav Kysela <perex at perex.cz>
Linux Sound Maintainer; ALSA Project; Red Hat, Inc.