Truly Free drivers could use a stable API too [LWN.net]

Truly Free drivers could use a stable API too

Posted Nov 10, 2005 22:52 UTC (Thu) by Duncan (guest, #6647)
In reply to: Truly Free drivers could use a stable API too by kfiles
Parent article: On binary drivers and stable interfaces

>> To install a new kernel you have
>> to reboot - very Windoze like :-(
>
> Well, to install a new card you
> have to reboot too[.]
>
> Now for USB stuff and network protocols[...]

Actually, for hotpluggable stuff like USB, there are kernel modules.
Kernel modules can be compiled separately, against the codebase used to
compile the running kernel, and can then be modprobed, without rebooting.

As for closer to the core hotpluggability, memory and CPUs and the like,
the kernel isn't quite there yet, but support is actively being worked up
and is already there to some degree. For this sort of support, modules
aren't generally needed, because support for a base level will be compiled
in and additional CPUs or memory use the existing support.

Of course, one still has to reboot (or kexec) to a new kernel if switching
to hardware of a different architecture. However, I don't know if
anything supports that, and the call for such support isn't that great,
anyway, tho it could be useful in certain high availability situations.

BTW, the user mode drivers comments someone made are a good idea, as well.
There's nothing stopping that (tho more integrated/direct kernel support
in some cases would be very useful, think fuse implementation before and
after the kernel support for it), and indeed, the kernel's GPL preamble
specifically states that the restrictions of the GPL do NOT apply to
userspace, so binary drivers are with no controversy completely legal
there (altho there remains disagreement of whether they are /moral/, but
it's the usual controversy of whether /any/ binary-only code is /moral/).
The problem of course is the performance bite. It's fine in some cases,
particularly where there's direct kernel support for the userspace drivers
as with fuse, but would suck for something like NVidia's video drivers.
Very good point made, none-the-less.

Duncan

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Truly Free drivers could use a stable API too

Posted Nov 11, 2005 1:48 UTC (Fri) by giraffedata (subscriber, #1954) [Link]

Actually, for hotpluggable stuff like USB, there are kernel modules. Kernel modules can be compiled separately, against the codebase used to compile the running kernel, and can then be modprobed, without rebooting.

In this thread, we're talking about unstable APIs. You probably cannot just separately compile the loadable kernel module against the currently running kernel because the base kernel / device driver LKM interface has changed.

The original poster makes the point that with a stable API, your method would work. But without one, you need to upgrade your entire kernel in order to use a new loadable kernel module. And a reboot is just one of the pains of doing that.

User space drivers solves the problem only if we assume that the user space interface is stable like user space interfaces we know today.