Re: [PATCH 0/3] New firewire stack

Kristian Høgsberg
2006-12-06T22:33:12Z

Stefan Richter wrote:
...
>> Another point is the various streaming drivers. There used to be 5 different
>> userspace streaming APIs in the linux1394: raw1394, video1394, amdtp, dv1394
>> and rawiso. Recently, amdtp (audio streaming) has been removed, since with
>> the rawiso interface, this can be done in userspace. However the remaining 4
>> interfaces have slightly disjoint feature sets and can't really be phased out.
>
> The old iso API of (lib)raw1394 has been marked deprecated and
> undocumented in libraw1394's documentation for some time, and will go
> away in 2007.
>
> Dv1394 might go away in 2007 too if there is enough effort to move
> high-profile users over to rawiso a.k.a. the current iso API of
> (lib)raw1394.
>
> I suppose video1394 might get a viable migration path with your new
> driver, if you and interested developers put effort into development
> (and help with deployment) of a proper replacement.

As discussed on linux1394-devel, it may be possible to do a thin video1394
compatibility driver for this one, but since the biggest user of this
interface is libdc1394, it is probably better to just write a new iso
streaming backend for this library. libdc1394 already supports different
streaming backends. For non-libdc1394 users of video1394, the interface I'm
providing is very close to the video1394 ioctl interface, so porting should be
easy enough.

>> In the long run, supporting 4 different interfaces that does almost the same
>> thing isn't feasible. The streaming interface in my new stack (only
>> transmission implemented at this point) can replace all of these interfaces.
>
> You have to look at the matter not only from the POV of API design but
> also of deployment and support.

My POV here *is* about deployment and support, but from the kernel side of
things. If you commit yourself to long time support for the firewire stack,
would you prefer 4 slightly different streaming drivers with different user
space interfaces, or just one userspace driver with one userspace interface,
that enables the 4 different types of streaming to be done in userspace? The
design of the streaming interfaces have been focused on enabling all these
ad-hoc, in-kernel drivers to move to userspace, to make it feasible to
actually support the stack.

Kristian