Hello Michał,

09.01.2022 02:35, Michał Mirosław пишет:

BTW, I couldn't find a right description of my idea of unifying the
chains before, so let me sketch it now.

The idea is to have a single system-off chain in which the callback
gets a mode ({QUERY_*, PREP_*, DO_*} for each of {*_REBOOT, *_POWEROFF, ...?).
The QUERY_* calls would be made in can_kernel_reboot/poweroff(): all
would be called, and if at least one returned true, then the shutdown
mode would continue. All of PREP_* would be called then. After that
all DO_* would be tried until one doesn't return (succeeded or broke
the system hard). Classic for(;;); could be a final fallback for the
case where arch/machine (lowest priority) call would return instead
of halting the system in machine-dependent way. The QUERY and PREP
stages could be combined, but I haven't thought about it enough to
see what conditions would need to be imposed on the callbacks in
that case (maybe it's not worth the trouble, since it isn't a fast
path anyway?). The goal here is to have less (duplicated) code in
kernel, but otherwise it seems equivalent to your API proposal.

Thank you again for yours proposal! IMO, it's much more important to
keep the core code simple and maintainable, rather than try to optimize
it without a very good reason, given that this isn't a hot code path at
all and saving a couple of bytes won't be noticeable. The poweroff,
restart and reboot were separated before this series and I'm finding
that it's easier to follow the code when it's structured that way. I'm
not convinced that we need to change it.