Hello Christian, A tweak to one point from my mail of a few minutes ago... On 9/19/19 6:04 AM, Michael Kerrisk (man-pages) wrote: > A further question... We now have three ways of getting a > process file descriptor [*]: > > open() of /proc/PID > pidfd_open() > clone()/clone3() with CLONE_PIDFD > > I thought the FD was supposed to be equivalent in all three cases. > However, if I try (on kernel 5.3) poll() an FD returned by opening > /proc/PID, poll() tells me POLLNVAL for the FD. Is that difference > intentional? (I am guessing it is not.) Okay -- I made a misstep there, although my question remains. I got the POLLNVAL return because I had opened /proc/PID with the O_PATH flag. When I open /proc/PID with O_RDONLY, then poll() on the FD always returns immediately (i.e., before the target process has terminated), and the returned events are POLLIN+POLLOUT. Thanks, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/
