When PID=0 in early kernel_init, PID=1 has a skeleton running, this detection is not
the Busybox /sbin/init, but a place holder for when the real Busybox /sbin/init is do_execve'd and then the kernel flushes all the old process table information on the place holder of PID=1, then the real Busybox /sbin/init starts its life all fresh from the do_execve, no state remains. On 02/14/2018 06:49 AM, Denys Vlasenko wrote: > On Wed, Feb 14, 2018 at 4:29 AM, Deb McLemore <[email protected]> > wrote: >> On 02/13/2018 08:32 PM, Laurent Bercot wrote: >>>> Even when process=1 is started, it still leaves a window when the >>>> signal handler setup has not been completed. >>> Yes, but you can still use kill(pid, 0) to check whether init is >>> ready to receive signals: doublefork a zombie and repeatedly kill it >>> with signal 0. When you get -1 ESRCH, it means init has reapt the >>> zombie, so it's in its reaping loop, and at that point you know it >>> has installed its signal handlers. >>> >>> See http://lists.busybox.net/pipermail/busybox/2017-October/085888.html >>> >>> That's arguably uglier than using abstract sockets, but it can >>> be done without modifying the init code at all. >> From the original thread, we tried the suggestion, but when the do_execve is >> done from kernel_init >> >> for Busybox /sbin/init (to start PID=1) all process zombies are flushed (the >> usermode helper that kicks >> >> Busybox /sbin/poweroff started by PID=2, before PID=1 is do_execve'd from >> kernel init). So when the line is crossed >> >> when PID=1 begins all zombies and pre-work are flushed, so nothing is >> carried over into the life of PID=1 >> to synchronize with or detect when the signals are properly setup. > You can detect this: before init is started, kill(1,0) should be giving ESRCH. > Thus: first wait for kill(1,0) to return 0. > Then, do a child reaping test. Or just sleep(1). :] > _______________________________________________ busybox mailing list [email protected] http://lists.busybox.net/mailman/listinfo/busybox
