Frank Griffin wrote:
> I understand your explanation, but it raises a question for me that may
> be (some of) what is confusing Steve.
>
> If all these versions of libGL are different, why don't the various
> applications that want a specific version require them by specific name
> ?

Because the applications want libGL.so.1, they don't care which
implementation.

> Then they could all be installed side-by-side, and the dynamic linker
> could resolve them without the use of alternatives, no ?

Yes.

> I thought that the raison d'etre of alternatives was to allow a sysadmin
> to seamlessly switch between different packages providing exactly the
> same service with exactly the same API, e.g. postfix and sendmail.

Yes.

> In
> this case it looks like it's being used to allow mesa and the various
> nvidia drivers to each blissfully assume that everybody else uses the
> same version of the library they need.

I don't understand what you are saying here.

NVIDIA-provided libGL.so.1 provides a NVIDIA implementation of the
OpenGL API, and it only works when used with proprietary NVIDIA X.org
driver.

> Or is the point that everyone using libGL *has* to be using the same
> version as the video driver ? In that case, alternatives makes more
> sense.

I don't understand. libGL users have to use the same version of libGL as
video drivers? That doesn't make any sense to me.

> But I have two cooker systems, one with an nvidia card and one
> without. Mesa is installed on both. On the nvidia system,
> /etc/alternatives/gl_conf is symlinked to /etc/nvidia-current/ld.so.conf
> and on the other it is symlinked to /etc/ld.so.conf.d/GL/standard.conf.
> So how is mesa expected to work on both ?

Mesa libGL only works on the non-nvidia system. On the NVIDIA system the
NVIDIA-provided libGL is used instead.

--
Anssi Hannula