Messages in this thread | | | From | (Eric W. Biederman) | Date | Mon, 28 Sep 2015 11:57:39 -0500 | Subject | Re: [PATCH RFC v3 2/2] pidns: introduce syscall getvpid |
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Konstantin Khlebnikov <khlebnikov@yandex-team.ru> writes:
> If pid is negative then getvpid() returns pid of parent task for -pid.
Now that I am noticing this. I don't think I have seen any discussion about justifying a syscall getting another processes parent pid. My apologies if I just missed it.
Why do we want the the parent pid? We can we usefully do with it? Is proc really that bad of an interface?
Fetching a parent pid feels like a separate logical operation from pid translation. Which makes me a bit uneasy about this part of the conversation.
> Examples: > getvpid(pid, ns, -1) - get pid in our pid namespace > getvpid(pid, -1, ns) - get pid in container > getvpid(pid, -1, ns) > 0 - is pid is reachable from container? > getvpid(1, ns1, ns2) > 0 - is ns1 inside ns2? > getvpid(1, ns1, ns2) == 0 - is ns1 outside ns2? > getvpid(1, ns, -1) - get init task of pid-namespace > getvpid(-1, ns, -1) - get reaper of init task in parent pid-namespace > getvpid(-pid, -1, -1) - get ppid by pid
As I step back and pay attention to this case I am half wondering if perhaps what would be most useful is a file descriptor that refers to a pid and an updated set of system calls that takes pid file descriptors instead of pids.
Something like:
getpidfd(int pidnsfd, pid_t pid);
waitfd(int pidfd, int *status, int options, struct rusage *rusage);
killfd(int pidfd, int sig);
clonefd(...);
And perhaps: pid_nr_ns(int pidnsfd, int pidfd);
parentfd(int pidfd);
Eric
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