Re: [FFmpeg-devel] [PATCH v2 0/3] hwcontext_vaapi: dlopen libva-x11 and libva-drm

[Mark Thompson <sw@jkqxz.net>]

On 20/07/2022 17:41, Emil Velikov wrote:
> On Tue, 19 Jul 2022 at 19:16, Nicolas George <george@nsup.org> wrote:
>>
>> Emil Velikov (12022-07-19):
>>> As you may know the libva* set of libraries share an internal ABI
>>> between them. In a resent libva commit, the va_fool API was removed.
>>>
>>> Thus if one is to mix different versions of libva.so and libva-x11.so
>>> they will get an error, leading to a crash of the whole stack.
>>>
>>> The simple solution is
>>
>> ... a configure check.
>>
>> If the person who installs replaces a library with another, it is their
>> responsibility to check they are compatible.
>>
> 
> While I wholeheartedly agree, it's not so easy to enforce compile time
> decisions at runtime. In the past, I have debugged and reported issues
> where Linux distributions do not enforce the above.
> 
> We do have the typical Linux distribution model (where we have dozens
> upon distros) and other distribution models. IMHO checking each
> instance and combination doesn't scale. We could bring awareness to
> the issue in say distribution/workflow X, which sadly may come as
> finger-pointing and thus alienating.
> 
> Hope that makes sense and the team is willing to consider the extra 90
> lines worth of code.

The argument "libfoo can be broken in some particular configuration, so lets use dlopen() to make errors happen later" seems like it applies to every library.  Why is this case so special?  Who are the users running into this specific problem and who are stuck with broken versions they can't update?

(Also, shouldn't lazy binding save people in this situation if they don't actually use the feature, as they presumably don't if barfing at runtime makes sense?)

Tbh I don't think FFmpeg libraries are the right place to be putting this sort of workaround.

Thanks,

- Mark
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