Messages in this thread | | | From | Andy Lutomirski <> | Subject | Re: [PATCH v2 0/5] pid: add pidfd_open() | Date | Sun, 31 Mar 2019 14:09:03 -0600 |
| |
> On Mar 30, 2019, at 11:24 AM, Linus Torvalds <torvalds@linux-foundation.org> wrote: > >> On Sat, Mar 30, 2019 at 10:12 AM Christian Brauner <christian@brauner.io> wrote: >> >> >> To clarify, what the Android guys really wanted to be part of the api is >> a way to get race-free access to metadata associated with a given pidfd. >> And the idea was that *if and only if procfs is mounted* you could do: >> >> int pidfd = pidfd_open(1234, 0); >> >> int procfd = open("/proc", O_RDONLY | O_CLOEXEC); >> int procpidfd = ioctl(pidfd, PIDFD_TO_PROCFD, procfd); > > And my claim is that this is three system calls - one of them very > hacky - to just do > > int pidfd = open("/proc/%d", O_PATH);
Hi Linus-
I want to re-check this because I think Christian’s example was bad. I proposed these ioctls, but that wasn’t the intended use. The real point is:
int pidfd = new_improved_clone(...);
To be useful, this type of API *must* work without proc mounted.
And, later:
openat(fd to pidfd’s proc directory, “status”, ...);
And we want a non-utterly-crappy way to do this. The ioctl is certainly ugly, but it *works*.
Another approach is:
pid_t pid = pidfd_get_pid(pidfd); sprintf(buf, “/proc/%d”, pid); int procfd = open(buf, O_PATH); if (pidfd_get_pid(pidfd) != pid) { we lose; }
But this is clunky.
Do you think the clunky version is okay, or do you have a suggestion for making it better?
—Andy
| |