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    SubjectRe: [RFC][PATCH 0/3] fork: Add the ability to create tasks with given pids
    On 11/25, Pavel Emelyanov wrote:
    >
    > On 11/25/2011 08:22 PM, Oleg Nesterov wrote:
    > > On 11/25, Pavel Emelyanov wrote:
    > >>
    > >> The proposal is to implement the PR_RESERVE_PID prctl which allocates and puts a
    > >> pid on the current. The subsequent fork() uses this pid,
    > >
    > > Oh. This is subjective, yes, but this doesn't clean to me.
    > >
    > > Amd why?? On the running system PR_RESERVE_PID can obviously fail anyway.
    > > It only helps to avoid the race with another fork.
    >
    > No. It can fail if you try to allocate a pid with given number. The API allows for
    > pid generation. AFAIU this can help with Pedro's requirements to resurrect task with
    > the same pid value it used to have before.

    Yes gdb can do fork() in a row (until it unreserves the pid) and the
    pid will be the same.

    OK, I misunderstood. I thought you insist that PR_RESERVE_PID itself
    is reliable.

    But this can only work in the simplest case. How you can restore the
    multithread tracee? You need to unreserve/reserve the previous pid,
    and we have the same problems again, no?

    > > Yes, and this task_struct->rsv_pid acts as implicit parameter for the
    > > next clone(). Doesn't look very nice to me. Plus the code complications.
    >
    > Well, the last_pid is also an implicit parameter for the next clone() with sysctl
    > approach :)

    Yes. but it is already here ;)

    Oleg.



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