On Wed, Feb 14, 2018 at 4:29 AM, Deb McLemore <de...@linux.vnet.ibm.com> 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 firstname.lastname@example.org http://lists.busybox.net/mailman/listinfo/busybox