Messages in this thread | | | Subject | Re: + prctl-add-pr_setget_child_reaper-to-allow-simple-process-supervision .patch added to -mm tree | From | Kay Sievers <> | Date | Thu, 18 Aug 2011 23:55:15 +0200 |
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On Thu, Aug 18, 2011 at 23:23, Linus Torvalds <torvalds@linux-foundation.org> wrote: > On Thu, Aug 18, 2011 at 11:11 AM, Kay Sievers <kay.sievers@vrfy.org> wrote: >> >> How about this? It: >> - uses task->real_parent to walk up the chain of parents. > > If I read this right, it does that for all the normal cases too. > Disgusting. Slowing down the *usual* UNIX case for your new made-up > case that nobody actually uses is not acceptable.
Re-parenting is not a *usual* operation, usual exit()s have a parent and do not trigger that code. And in most cases of double-forking it is a one step, which is almost the same than it was before. Only if we skip multiple parents it will get the check, which is cheap anyway.
> So NAK. We're not slowing down normal code for some new feature that > realistically will never be used by any normal applications.
It will be used for all new service managers. UNIX is a pain if you want to watch your children regarding double-forking, if you are not init.
And it will clean up the mess the desktop stuff is putting in 'ps afx'. Here is the before/after output:
253 ? Ss 0:00 /bin/dbus-daemon --system --address=systemd: --nofork --systemd-activation 294 ? Sl 0:00 /usr/libexec/polkit-1/polkitd 328 ? S 0:00 /usr/sbin/modem-manager 608 ? Sl 0:00 /usr/libexec/colord 658 ? Sl 0:00 /usr/libexec/upowerd 819 ? Sl 0:00 /usr/libexec/imsettings-daemon 916 ? Sl 0:00 /usr/libexec/udisks-daemon 917 ? S 0:00 \_ udisks-daemon: not polling any devices
294 ? Ss 0:00 /bin/dbus-daemon --system --address=systemd: --nofork --systemd-activation 426 ? Sl 0:00 \_ /usr/libexec/polkit-1/polkitd 449 ? S 0:00 \_ /usr/sbin/modem-manager 635 ? Sl 0:00 \_ /usr/libexec/colord 705 ? Sl 0:00 \_ /usr/libexec/upowerd 959 ? Sl 0:00 \_ /usr/libexec/udisks-daemon 960 ? S 0:00 | \_ udisks-daemon: not polling any devices 977 ? Sl 0:00 \_ /usr/libexec/packagekitd
It's a pretty nice way for an admin too see what's going on on that box, even with good old 'ps'.
It will also dramatically simplify the handling of started services from a service manager which double-fork for only historic reasons and make proper service supervision a nightmare if you are not PID 1.
Upstart ptraces all started services to accomplish something similar. I doubt we want to go that road, but if you prefer ... :)
If you want, we can make the forked processes inherit a flag if the 'subreaper' should be looked up at all. Then we have almost zero overhead if the feature isn't used. You think that's needed?
Thanks, Kay
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