Hi Gábor, Gábor Boskovits <gboskov...@gmail.com> skribis:
> Ludo's FOSDEM talk inspired me to share some thoughts that I encountered > during my time at my previous position where we designed an init system. Oh! > The fist things are the specialities of the pid 1 processes: > - they own the pid namespace where they are pid 1 (this works > automatically, there is nothing to do here) > - they do not have default signal handling (this means that when running as > pid1 you might want to have a default set of signal handlers installed) > - the orphaned processes from the pid namespace get automatically > reparented to them (on linux there is a concept called a subreaper process > that allows to delegate this responsibility downwards, having the orphaned > processes reparented to the subreapers, to be able to manage process > subtrees without the need to spin up a new nested pid namespace, we might > want to provide configuration to enable the subreaper behavior) I was aware of this so hopefully this is all good. > Also, now pid 1 exist on all pid namespace of the pid namespace hierarchy, > and also from the outer nesting levels these are also visible under a > different pid. We might take a look how shepherd interacts with these. Agreed. In commit f6a77c1ab28f07c496f799ff0bdb953b1fe628b2, ‘gnu-build-system.scm’ was changed precisely for that reason: so that PID 1 would take care of reaping dead processes, which was not the case before and a source of problems (see <https://issues.guix.gnu.org/30948>.) > On the process management front a quite important new API is available in > newer linux kernels, called pidfd, which allows to have a file descriptor > interface to a process, making signaling and waiting for processes much > less error prone. Yup, pidfd looks nice! So far, the overall design decision was to try and avoid relying on Linux interfaces not implemented on the Hurd. For ‘signalfd’, there’s a fallback to good old signal handlers when not running on Linux; it’s less pleasant than ‘signalfd’ and it increases the surface to test, so I’d rather not do it too much. If you take a look at the Shepherd’s code, do share your findings. Thanks for your feedback! Ludo’.
