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Re: [GSoC] GNU/Hurd Sound Support

From: Mohammed Gamal
Subject: Re: [GSoC] GNU/Hurd Sound Support
Date: Tue, 1 Apr 2008 10:59:09 +0200

On Tue, Apr 1, 2008 at 4:46 AM,  <olafBuddenhagen@gmx.net> wrote:
> Hi,
>  On Mon, Mar 31, 2008 at 10:22:11PM +0200, Mohammed Gamal wrote:
>  > This is kind of a late follow up to these threads [1][2].
>  Well, why not just reply in that thread, then? :-) That would have made
>  it much easier to keep track...

The old threads were inquiries about different ideas, now that I am
settled with this one, I thought about starting it in a new thread to
dedicate for discussing that particular project.

>  > I am quite interested interested in adding sound support in Hurd, yet
>  > I am completely new to Hurd and also a Linux kernel newbie. I have a
>  > basic understanding of Linux drivers, and character devices in
>  > particular. Would it be suitable for someone with my experience to
>  > apply for such project?
>  Applying can never hurt :-)
>  Whether your experience is sufficient, is hard to judge. It depends
>  greatly on your general programming experience, and your ability to
>  grasp new concepts quickly.
>  You could try to write some first bit of code related to this project
>  right now (of course, we will assist you as well as we can!) -- seeing
>  what the progress you make with that, would allow us to form an opinion
>  about how likely you will be able to finish the project in time :-)

I have good experience with C/C++ and I am familiar with POSIX API, my
coding experience was generally in userspace, I didn't do anything
serious in kernel space. As for your suggestion, I think it's a very
good idea.

>  > I've read the GNU/Hurd Hacking Guide and could get a sense of how
>  > translators work and interact with system libraries and how do those
>  > in turn interact with the kernel.
>  This is a good start :-)
>  > So, the picture I am getting is that to add sound support we'll need a
>  > system library (which we can call 'libsound' for example) which should
>  > provide a general interface to sound hardware (analogous to ALSA in
>  > Linux), and for each sound device one has to write a translator that
>  > will map device calls (ioctls, reads/writes ...etc) to Mach device
>  > calls, so am I getting the right picture here?
>  I'm not sure, but my impression is that you somehow got it backwards...
>  The actual drivers live inside Mach (which is suboptimal, but not easy
>  to change...); and Mach offers access to them through it's device
>  interface. This is similar in what it does to UNIX device files, but
>  it's not compatible -- Mach knows nothing about UNIX files. So we need a
>  translator in user space (like we already have for various other kinds
>  of devices), which translates POSIX calls into Mach device calls.

Sorry, there was some misunderstanding of the term "translator" on my
part here. What I mean is that we'd need a program, rather than a
translator,  for each sound card that'd talk "libsound" that'd in turn
pass messages to the Mach kernel. However, does what you say here mean
that we'd rather have to write the drivers directly in the Mach

>  > As for the driver, I am thinking about porting the Ensoniq 1370 driver
>  > as it's emulated under QEMU, do you think this would be a good idea?
>  Yes, that's probably a very good idea.
>  In fact, Richard Braun (syn on IRC) has once tried porting the driver,
>  and had it mostly working, but there was a serious bug he couldn't track
>  down, so he gave up. You could try to contact him -- perhaps you could
>  use his code as a starting point, or at least get some advice.
>  -antrik-

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