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    SubjectRe: [PATCH] exit: PR_SET_ANCHOR for marking processes as reapers for child processes
    On Tue, 21.12.10 12:05, Scott James Remnant ( wrote:

    > > PID namespaces primarily provide an independent PID numbering scheme for
    > > a subset of processes, i.e. so that identical may PIDs refer to different
    > > processes depending on the namespace they are running in. As a side
    > > effect this also provides init-like behaviour for processes that aren't
    > > the original PID 1 of the operating system. For systemd we are only
    > > interested in this side effect, but are not interested at all in the
    > > renumbering of processes, and in fact would even really dislike if it
    > > happened. That's why PR_SET_ANCHOR is useful: it gives us init-like
    > > behaviour without renaming all processes.
    > >
    > Right, but I don't get why you need this behavior to supervise either
    > system or user processes. You already get all the functionality you
    > need to track processes via either cgroups or the proc connector (or a
    > combination of both).

    Well, we want a clean way to get access to the full siginfo_t of the
    SIGCHLD for the main process of a service. the proc connector is awful
    and cgroups does not pass siginfo_t's back to userspace, hence the
    cleanest way to get this done properly and beautifully is to make the
    session systemd a mini-init via PR_SET_ANCHOR, because then the per-user
    systemd's and the per-system systemd can use the exact same code to
    handle process managment.

    > So is this really just about making ps look pretty, as Kay says?

    That's a side effect, but for me it's mostly about getting a simple way
    to get the SIGCHLDs, focussed on the children of the session manager and
    with minimal wakeups.


    Lennart Poettering - Red Hat, Inc.

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