Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx> 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
--
To unsubscribe from this list: send the line "unsubscribe linux-api" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
