RFC: propose helper script interface for writing rules

[Ella-0]

Proposes the use of a helper script to allow setting udev properties as a replacement for udev rules. For example setting ACP_IGNORE=1 on the visense pcm in apple silicon macs.

#!/bin/sh -e

if printf '%s\n' "$SYSNAME" | grep '^pcmC.*D2c$'
then
	printf 'ACP_IGNORE=1\n'
fi

[illiliti]

Thanks for working on this! I like the idea of passing control of properties to a helper script. It's much better option than adding special handling for properties.

[xplshn]

@illiliti Will this not be merged into master/main?

[illiliti]

@illiliti Will this not be merged into master/main?

I like the idea, so it is highly likely I'll merge this. Just need to sort out issues with code.

[Ella-0]

Addressed all comments and added an example rules script to contrib with the SOUND_INITIALIZED and ACP_IGNORE stuff. Note: this on its own will not fix pipewire since pipewire still depends on the enumeration of parent devices

[illiliti]

Note: this on its own will not fix pipewire since pipewire still depends on the enumeration of parent devices

One could access parent device via $SYSPATH/../ or $SYSPATH/device/, so unless I'm missing something it is indeed possible to fix pipewire.

[Ella-0]

Note: this on its own will not fix pipewire since pipewire still depends on the enumeration of parent devices

One could access parent device via $SYSPATH/../ or $SYSPATH/device/, so unless I'm missing something it is indeed possible to fix pipewire.

The problem with pipewire is it enumerates the following devices

/sys/devices/platform/sound/sound/card0/pcmC0D0p
/sys/devices/platform/sound/sound/card0/pcmC0D1p
/sys/devices/virtual/sound/timer
/sys/devices/platform/sound/sound/card0/pcmC0D0c
/sys/devices/platform/sound/sound/card0/pcmC0D2c
/sys/devices/platform/sound/sound/card0/controlC0

however the following is intended. card0 is missing. this is due to scan_devices working on /sys/dev/{char,block} but card? does not have an associated character or block device so isn't enumerated.

/sys/devices/platform/sound/sound/card0
/sys/devices/platform/sound/sound/card0/pcmC0D0p
/sys/devices/platform/sound/sound/card0/pcmC0D1p
/sys/devices/virtual/sound/timer
/sys/devices/platform/sound/sound/card0/pcmC0D0c
/sys/devices/platform/sound/sound/card0/pcmC0D2c
/sys/devices/platform/sound/sound/card0/controlC0

[illiliti]

Ah! Right. Forgot about this one. Well, we could switch our enumeration approach to appease pipewire. Let's keep it for later.

[illiliti]

close out_pipe and destroy actions

[illiliti]

int ret = posix_spawn(...);
posix_spawn_file_actions_destroy(&actions);
close(out_pipe[1]);
if (ret != 0) {
    close(out_pipe[0]);
    return -1;
}

[illiliti]

You are still leaking out_pipe and actions here. Consider adopting the above code to fix the leak.