Remove agetty services for missing devices

[raindev]

The most common offenders are agetty-hvsi0 and agetty-hvc0. agetty
services started for devices that do not exist end up failing with

cannot open as standard input: No such file or directory

runit restarts such services resulting in syslog being flooded
with error messages.

Closes #193

---

A "test case":

$ ls /var/service | grep agetty
agetty-hvc0
agetty-hvsi0
agetty-tty1
agetty-tty2
agetty-tty3
agetty-tty4
agetty-tty5
agetty-tty6

$ cat /tmp/agetty
#!/bin/bash
set -euo pipefail

for service in /var/service/agetty-*; do
    if [ ! -e /dev/"$(cut -d'-' -f2 <<< "$service")" ]; then
        rm -v "$service"
    fi
done

$ sudo /tmp/agetty
removed '/var/service/agetty-hvc0'
removed '/var/service/agetty-hvsi0'

$ ls /var/service/ | grep agetty
agetty-tty1
agetty-tty2
agetty-tty3
agetty-tty4
agetty-tty5
agetty-tty6

Note that I only verified the snipped outside of the installer. If you think it makes sense to test it as a part of the installation process, I can do that too.

[Duncaen]

for service in /var/service/agetty-*; do
    [ -e "/dev/${service#*agetty-}" ] || rm -v "$service"
done

But shouldn't this be done in $TARGETDIR?

[q66]

we should instead figure out why those services are getting auto-enabled in the first place, and then fix that

[Duncaen]

This dracut hook enables all installed services on boot that are not excludes: https://github.com/void-linux/void-mklive/blob/master/dracut/vmklive/services.sh

[q66]

well, since this dracut hook includes ttyS* already, it would make sense to add hvc0 and hvsi0 in there as well

[q66]

actually, i have that already done here, along with proper enablement of serial console in live: void-ppc@8a3c5c0

[raindev]

Great to see this fixed, albeit not the way I imagined.

How would the people that needs hvc0/hvsi consoles would enable them? Would that be specifying console on the command line (similarly as done for GCP images here), taken into account by dracut script of the live ISO (here)?

[q66]

yeah just add the console= you want, e.g. console=hvc0 or console=ttyS0 and the new dracut hook will pick it up and enable the service

the only people who need hvc0 are users of openpower machines (ibm power8/power9) which expose the serial port through a firmware abstraction rather than directly, and some xen users; hvsi0 will have even fewer users