[alsa-devel] External PCM hook SO is dlclosed after calling install, making it hard to have hooks in it

[Paul Fertser]

On Tue, Jun 30, 2009 at 08:33:15AM +0200, Takashi Iwai wrote:
> > It looks like we're talking about different things. You seem to be
> > talking about external PCM plugins, i'm talking about external functions
> > for the "hook" PCM plugin. The code i question is in pcm/pcm_hooks.c
> > in function snd_pcm_hook_add_conf:
> > 
> >         if (err >= 0) {
> >                 if (args && snd_config_get_string(args, &str) >= 0) {
> >                         err = snd_config_search_definition(root,
> >                 "hook_args", str, &args);
> >                         if (err < 0)
> >                                 SNDERR("unknown hook_args %s", str);
> >                         else
> >                                 err = install_func(pcm, args);
> >                         snd_config_delete(args);
> >                 } else
> >                         err = install_func(pcm, args);
> >                 snd_dlclose(h);
> >         }
> 
> Ah, I understand now.  Yes, this looks like a bug.
> Meanwhile, it makes another bug if we just remove it.  There would be
> no dlclose(), then.  It'd need resource tracking.

Exactly the reason i haven't tried to make a proper patch ;)

>  A lack of dlclose is no serious bug, though.

I hope you know better than me ;)

> So... just removing snd_dlclose() there fixes your problem?
> If yes, I'll commit the fix.

TBH, i've not tried but i'm pretty sure it will fix the problem. I
tried with dlopen workaround (to increase the refcounter) in install
function and i tried with LD_PRELOAD'ing the library before starting
an alsa app; both workarounds worked.

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