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    SubjectRe: [PATCH v4] pidns: introduce syscall translate_pid
    On 10/13, Konstantin Khlebnikov wrote:
    >
    >
    > On 13.10.2017 19:05, Oleg Nesterov wrote:
    > >
    > >I won't insist, but this suggests we should add a new helper,
    > >get_ns_by_fd_type(fd, type), and convert get_net_ns_by_fd() to use it
    > >as well.
    >
    > That was in v3.
    >
    > I'll prefer to this later, separately. And replace fget with fdget which
    > allows to do this without atomic operations if task is single-threaded.

    OK, agreed,

    > >Stupid question. Can't we make a simpler API which doesn't need /proc/ ?
    > >I mean,
    > >
    > > sys_translate_pid(pid_t pid, pid_t source_pid, pid_t target_pid)
    > > {
    > > struct pid_namespace *source_ns, *target_ns;
    > >
    > > source_ns = task_active_pid_ns(find_task_by_vpid(source_pid));
    > > target_ns = task_active_pid_ns(find_task_by_vpid(target_pid));
    > >
    > > ...
    > > }
    > > > Yes, this is more limited... Do you have a use-case when this is not enough?
    >
    > That was in v1 but considered too racy.

    Hmm, I don't understand...

    Yes sure, this is racy but open("/proc/$pid/ns/pid") is racy too?

    OK, once you do fd=open("/proc/$pid/ns/pid") you can use this fd even after
    its owner exits, while find_task_by_vpid() will fail or find another task if
    this pid was already reused.

    But once again, do you have a use-case when this is important?

    > But we could merge both ways:
    >
    > source >= 0 - pidns fs
    > source < 0 - task_pid = -source

    But for what? I must have missed something...

    Oleg.

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