Messages in this thread | | | Date | Mon, 23 Sep 2019 16:47:13 +0200 | From | Christian Brauner <> | Subject | Re: For review: pidfd_open(2) manual page |
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On Mon, Sep 23, 2019 at 12:53:09PM +0200, Florian Weimer wrote: > * Michael Kerrisk: > > > SYNOPSIS > > int pidfd_open(pid_t pid, unsigned int flags); > > Should this mention <sys/types.h> for pid_t? > > > ERRORS > > EINVAL flags is not 0. > > > > EINVAL pid is not valid. > > > > ESRCH The process specified by pid does not exist. > > Presumably, EMFILE and ENFILE are also possible errors, and so is > ENOMEM.
So, error codes that could surface are: EMFILE: too many open files ENODEV: the anon inode filesystem is not available in this kernel (unlikely) ENOMEM: not enough memory (to allocate the backing struct file) ENFILE: you're over the max_files limit which can be set through proc
I think that should be it.
> > > A PID file descriptor can be monitored using poll(2), select(2), > > and epoll(7). When the process that it refers to terminates, the > > file descriptor indicates as readable. Note, however, that in the > > current implementation, nothing can be read from the file descrip‐ > > tor. > > “is indicated as readable” or “becomes readable”? Will reading block? > > > The pidfd_open() system call is the preferred way of obtaining a > > PID file descriptor. The alternative is to obtain a file descrip‐ > > tor by opening a /proc/[pid] directory. However, the latter tech‐ > > nique is possible only if the proc(5) file system is mounted; fur‐ > > thermore, the file descriptor obtained in this way is not pol‐ > > lable. > > One question is whether the glibc wrapper should fall back back to the > /proc subdirectory if it is not available. Probably not.
No, that would not be transparent to userspace. Especially because both fds differ in what can be done with them.
> > > static > > int pidfd_open(pid_t pid, unsigned int flags) > > { > > return syscall(__NR_pidfd_open, pid, flags); > > } > > Please call this function something else (not pidfd_open), so that the > example continues to work if glibc provides the system call wrapper.
Agreed!
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