[BRLTTY] Honor distribution LDFLAGS when building drivers

[Jaroslav Skarvada]

----- Original Message -----
> [quoted lines by Jaroslav Skarvada on 2018/05/24 at 05:29 -0400]
> 
> >In rawhide I changed systemd service WantedBy to:
> >WantedBy=default.target emergency.target
> 
> Thanks. Would it make sense to also add rescue.target?
>
OK, I think it could be helpful, I will add it.

> >Regarding dracut module it seems to be a bit more tricky, but we will
> >try to implement one. I am ready to receive patches / PR if anybody
> >wants to contribute here :)
> 
> I could give it a try, but would benefit quite a bit from a few things since
> it's something I haven't done before. For example, a pointer to a document
> that
> describes what one needs to watch out for and pay attention to, what
> constraints there are, etc. Also, since a user would like to be able to
> override defaults with the braille driver and device, and probably the text
> table, it'd be good to know how to pass options to a dracut module and how
> that
> module receives them.
>
During the next week I should have an intern handy for this task.
He could prepare some proof of concept implementation. 

But if you want to play with it I think inspiration can be taken
from e.g. /usr/lib/dracut/modules.d/98syslog
There is some documentation (unfortunately incomplete) in manual page
dracut.modules. I am afraid there is nothing (or at least I don't know about)
like good tutorial or document describing best practices.

>From what I know:
It will require module-setup.sh, which should install runtime
shared libraries (libbluetooth should be probably enough, because other
libraries seems to be already present in the dracut image). Then it should
copy /etc/brltty.conf to the image, parse it and include all enabled drivers
and tables from the /etc/brltty and /usr/lib64/brltty. We could include
everything, but I think it would waste space in the image. Probably
better is to include only enabled things and maybe allow override through the
environmental variables (used when the dracut image is generated). It will
also require writing hooks (and installing them) for brltty service
startup and cleanup. We may also parse kernel command line arguments
for e.g. arguments prefixed by 'brltty.' to allow override for driver
selection during boot (from drivers installed in the dracut image).
Code snippets for all of this can be taken from the above mentioned syslog
module

thanks & regards

Jaroslav