mirror of https://github.com/mkerrisk/man-pages
pidfd_open.2: New page documenting pidfd_open(2)
Notes from a conversation on linux-man@ with Christian Brauner: [[ > [*} By the way, going forward, can we call these things > "process FDs", rather than "PID FDs"? The API names are what > they are, an that's okay, but these just as we have socket > FDs that refer to sockets, directory FDs that refer to > directories, and timer FDs that refer to timers, and so on, > these are FDs that refer to *processes*, not "process IDs". > It's a little thing, but I think the naming better, and > it's what I propose to use in the manual pages. The naming was another debate and we ended with this compromise. I would just clarify that a pidfd is a process file descriptor. I wouldn't make too much of a deal of hiding the shortcut "pidfd". People are already using it out there in the wild and it's never proven a good idea to go against accepted practice. ]] Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Michael Kerrisk
parent
34a975f8ae
commit
f110d8350c
|
|
@ -0,0 +1,164 @@
|
|||
.\" Copyright (c) 2019 by Michael Kerrisk <mtk.manpages@gmail.com>
|
||||
.\"
|
||||
.\" %%%LICENSE_START(VERBATIM)
|
||||
.\" Permission is granted to make and distribute verbatim copies of this
|
||||
.\" manual provided the copyright notice and this permission notice are
|
||||
.\" preserved on all copies.
|
||||
.\"
|
||||
.\" Permission is granted to copy and distribute modified versions of this
|
||||
.\" manual under the conditions for verbatim copying, provided that the
|
||||
.\" entire resulting derived work is distributed under the terms of a
|
||||
.\" permission notice identical to this one.
|
||||
.\"
|
||||
.\" Since the Linux kernel and libraries are constantly changing, this
|
||||
.\" manual page may be incorrect or out-of-date. The author(s) assume no
|
||||
.\" responsibility for errors or omissions, or for damages resulting from
|
||||
.\" the use of the information contained herein. The author(s) may not
|
||||
.\" have taken the same level of care in the production of this manual,
|
||||
.\" which is licensed free of charge, as they might when working
|
||||
.\" professionally.
|
||||
.\"
|
||||
.\" Formatted or processed versions of this manual, if unaccompanied by
|
||||
.\" the source, must acknowledge the copyright and authors of this work.
|
||||
.\" %%%LICENSE_END
|
||||
.\"
|
||||
.TH PIDFD_OPEN 2 2019-09-19 "Linux" "Linux Programmer's Manual"
|
||||
.SH NAME
|
||||
pidfd_open \- obtain a file descriptor that refers to a process
|
||||
.SH SYNOPSIS
|
||||
.nf
|
||||
.BI "int pidfd_open(pid_t " pid ", unsigned int " flags );
|
||||
.fi
|
||||
.SH DESCRIPTION
|
||||
The
|
||||
.BR pidfd_open ()
|
||||
system creates a file descriptor that refers to
|
||||
the process whose PID is specified in
|
||||
.IR pid .
|
||||
The file descriptor is returned as the function result;
|
||||
the close-on-exec flag is set on the file descriptor.
|
||||
.PP
|
||||
The
|
||||
.I flags
|
||||
argument is reserved for future use;
|
||||
currently, this argument must be specified as 0.
|
||||
.SH RETURN VALUE
|
||||
On success,
|
||||
.BR pidfd_open ()
|
||||
returns a nonnegative file descriptor.
|
||||
On success, \-1 is returned and
|
||||
.I errno
|
||||
is set to indicate the cause of the error.
|
||||
.SH ERRORS
|
||||
.TP
|
||||
.B EINVAL
|
||||
.I flags
|
||||
is not 0.
|
||||
.TP
|
||||
.B EINVAL
|
||||
.I pid
|
||||
is not valid.
|
||||
.TP
|
||||
.B ESRCH
|
||||
The process specified by
|
||||
.I pid
|
||||
does not exist.
|
||||
.SH VERSIONS
|
||||
.BR pidfd_open ()
|
||||
first appeared in Linux 5.3.
|
||||
.SH CONFORMING TO
|
||||
.BR pidfd_open ()
|
||||
is Linux specific.
|
||||
.SH NOTES
|
||||
Currently, there is no glibc wrapper for this system call; call it using
|
||||
.BR syscall (2).
|
||||
.PP
|
||||
The
|
||||
.BR pidfd_send_signal (2)
|
||||
system call can be used to send a signal to the process referred to by
|
||||
a PID file descriptor.
|
||||
.PP
|
||||
A PID file descriptor can be monitored using
|
||||
.BR poll (2),
|
||||
.BR select (2),
|
||||
and
|
||||
.BR 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 descriptor.
|
||||
.PP
|
||||
See also the discussion of the
|
||||
.BR CLONE_PIDFD
|
||||
flag in
|
||||
.BR clone (2).
|
||||
.SH EXAMPLE
|
||||
The program below opens a PID file descriptor for the
|
||||
process whose PID is specified as its command-line argument.
|
||||
It then monitors the file descriptor for readability
|
||||
.RB ( POLLIN )
|
||||
using
|
||||
.BR poll (2).
|
||||
When the process with the specified by PID terminates,
|
||||
.BR poll (2)
|
||||
returns, and indicates that the file descriptor is readable.
|
||||
.\"
|
||||
.SS Program source
|
||||
\&
|
||||
.nf
|
||||
#define _GNU_SOURCE
|
||||
#include <sys/syscall.h>
|
||||
#include <unistd.h>
|
||||
#include <poll.h>
|
||||
#include <stdlib.h>
|
||||
#include <stdio.h>
|
||||
|
||||
#ifndef __NR_pidfd_open
|
||||
#define __NR_pidfd_open 434
|
||||
#endif
|
||||
|
||||
static
|
||||
int pidfd_open(pid_t pid, unsigned int flags)
|
||||
{
|
||||
return syscall(__NR_pidfd_open, pid, flags);
|
||||
}
|
||||
|
||||
int
|
||||
main(int argc, char *argv[])
|
||||
{
|
||||
struct pollfd pollfd;
|
||||
int pidfd, ready;
|
||||
|
||||
if (argc != 2) {
|
||||
fprintf(stderr, "Usage: %s <pid>\en", argv[0]);
|
||||
exit(EXIT_SUCCESS);
|
||||
}
|
||||
|
||||
pidfd = pidfd_open(atoi(argv[1]), 0);
|
||||
if (pidfd == \-1) {
|
||||
perror("pidfd_open");
|
||||
exit(EXIT_FAILURE);
|
||||
}
|
||||
|
||||
pollfd.fd = pidfd;
|
||||
pollfd.events = POLLIN;
|
||||
|
||||
ready = poll(&pollfd, 1, \-1);
|
||||
if (ready == \-1) {
|
||||
perror("poll");
|
||||
exit(EXIT_FAILURE);
|
||||
}
|
||||
|
||||
printf("Events (0x%x): POLLIN is %sset\en", pollfd.revents,
|
||||
(pollfd.revents & POLLIN) ? "" : "not ");
|
||||
|
||||
exit(EXIT_SUCCESS);
|
||||
}
|
||||
.fi
|
||||
.SH SEE ALSO
|
||||
.BR clone (2),
|
||||
.BR kill (2),
|
||||
.BR pidfd_send_signal (2),
|
||||
.BR poll (2),
|
||||
.BR select (2),
|
||||
.BR epoll (7)
|
||||
Loading…
Reference in New Issue