[alsa-devel] [PATCH] alsa: support module on-demand loading for seq and timer

[Kay Sievers]

On Tue, Nov 23, 2010 at 17:56, Clemens Ladisch <clemens at ladisch.de> wrote:
> Kay Sievers wrote:
>> On Tue, Nov 23, 2010 at 16:45, Clemens Ladisch <clemens at ladisch.de> wrote:
>>> Kay Sievers wrote:
>>>> +MODULE_ALIAS("devname:snd/seq");
>>>
>>> The device name that alsa-lib tries to use for autoloading is actually
>>> /dev/aloadSEQ.
>>
>> That might need to be changed then, if something depends on that, but
>> nothing ever tries to open /dev/snd/seq.
>
> No, alsa-lib pokes /dev/aloadSEQ only if opening /dev/snd/seq has
> failed.  (Something historical, I believe.)

Yeah, that can probably removed some day. No system with dynamic
minors, which needs devtmpfs/udev,  can really have these nodes. And
static /dev systems have the real node anyway.

>>> So you're going to add the entries for card driver autoloading
>>> (/dev/aloadC*), too?
>>
>> No, we only ever handle single-instance devices with a single fixed
>> dev_t, not ones with an arbitrary number of device instances.
>>
>> Card drivers are loaded by hardware matches today, not on-demand, and
>> not by an card number.
>
> There are card drivers without matching hardware (such as MIDI over
> a serial port, or virtual devices).

Right, but they require manual configuration anyway, which is a
problem we can not solve here in such simple way. :)

This is only about the common case, making hotplug of sound hardware
work and on-demand setup work, without having init scripts that load
modules unconditionally, and things like this.

>> There are no configured numbered module aliases for sound cards
>> anymore, that can't work with today's setups.
>
> Just that it cannot work with systemd doesn't imply that nobody still
> uses it or that it could be dropped without regards for backward
> compatibility.

Right, the stuff might be in use in old setups.

It has nothing really to do with systemd, it's just nothing that
recent systems do. They all support dynamic reconfiguration without
prior setup of numbered lists of aliases, that get out-of-sync pretty
fast in today's hotplug world.

> Anyway, this patch is independent of ALSA's old autoload code.
> Applied.

Cool.

Many thanks,
Kay