Il 16 ottobre 2026 19:20:33 UTC, John Ogness <[email protected]> ha
scritto:
>
>I am still not clear how the rv tool will replace the existing in-kernel
>implementation. Right now violations call printk(), which conveniently
>show up in kernel logs and consoles. More importantly, there are the
>rtapp violation events, which makes it very easy to use ftrace and perf
>features to record traces, take actions, generate statistics, and dump
>backtraces on violations.
The plan is to keep everything you'd now do with perf/ftrace as plain stdout of
the RV tool. Right now you can see the same ftrace output using rv mon
<monitor> -t for in-kernel monitors (only deterministic automata).
We are missing stack traces (which I'd optionally add only on errors) and
perhaps other events (e.g. the -e in either tool if you aren't only interested
in errors/events of the monitor).
Anything else you may want to do passes through reactors (e.g. printk/panic or
others). See more later.
>Is it planned to pull all this out of the kernel but then somehow the rv
>tool allows ftrace, perf, and console to continue to work with
>violations? (For example, by somehow defining kprobes for violations and
>writing violation information to /dev/kmsg?) Or is the rv tool supposed
>to provide its own DIY variant of these features?
My plan isn't particularly strict right now. I'm aiming to allow BPF monitors
in the user space tool as an exploratory effort.
I don't think you would easily interact with ftrace/perf from those though.
If that's a requirement, you could probably call a kfunc from BPF and attach a
kprobe there. I would implement that from a reactor (violations only).
For a pure printk reactor, I drafted an implementation that calls directly
printk_deferred(), Alexei is suggesting to write to /dev/kmsg from user space
what BPF passes.
Since you were the one suggesting having a real printk, would your use-case
favour either solution? I'd expect some different latency if the log passes
from BPF to /dev/kmsg , but I'm not sure that's an issue for you.
Gabriele
