backlight(9): Emit brightness changes via devd(8)

[lme]

Summary

Teach backlight(9) to send brightness changes to devd(8), so one does
not need to poll for changes with backlight(8).

Output format:

!system=brightness subsystem=backlight0 type=change notify=42

Test Plan

• build a kernel
• run cat /var/run/devd.seqpacket.pipe | grep brightness
• change the background brightness using backlight(8)

[bcr]

OK from manpages. Make sure to bump the .Dd to the date when you commit it.

[imp]

sys/dev/backlight/backlight.c

88

So why not use device_get_nameunit(sc->dev) here?

[lme]

sys/dev/backlight/backlight.c

88

So why not use device_get_nameunit(sc->dev) here?

It's weird. When I change it to

devctl_notify("brightness", device_get_nameunit(sc->dev),
    "change", notify_buf);

I get drmn0 and not backlight0 as value for subsystem.

!system=brightness subsystem=drmn0 type=change notify=19