Plymouth re-read config when swap root ?

[Hans de Goede]

Hi,

On 11-09-2019 15:35, LAHAYE Olivier wrote:
> Hi,
> 
> I’ve written a specially crafted Plymouth them for SystemImager software that shows the progress in host installation.
> 
> When the host is installed, the SystemIlager hooks give back control to dracut and the system boots without need to reboot before.
> 
> Though, when doing so, Plymouth keep systemimager them active (with no use) while I’d prefer to switch to installed OS theme.
> 
> Is there a way to tell Plymouth that it’s new default them has changed and that it needs to re-read it? I’m using dracut in CentOS-7, but I need generic solution. Does dracut tells Plymouth that /sysroot has been swapped? If yes will Plymouth take car of that by re-reading the default theme or should I add a hook to help for the transition? What if the installed OS has no Plymouth installed?

plymouth does get told that the /sysroot has been swapped, but currently we do not re-read
the config from the real rootfs when this happens.

And TBH I'm not sure if that doing so is desirable...

For your specific use-case I would suggest adding a new command which the plymouth
client can send to plymouthd, this would then need to hide-spash, re-read config,
show-splash. but this will always make the boot flicker / look ugly on every boot
unless you figure out how to do this only after imaging.

Hmm, I guess you could add a reload_theme command to the client (and implement it
in the daemon) which checks if the theme name has changed and otherwise is a no-op.

With my plymouth-upstream hat on I must warn you though that I'm not sure if I would
accept a patch implementing this. That would depend on how invasive it is. If you can
make it reasonable clean then we can take it.

Regards,

Hans