pidfd: support PIDFD_NONBLOCK in pidfd_open() (6da73d15) · Commits · 戴 / test

Introduce PIDFD_NONBLOCK to support non-blocking pidfd file descriptors. Ever since the introduction of pidfds and more advanced async io various programming languages such as Rust have grown support for async event libraries. These libraries are created to help build epoll-based event loops around file descriptors. A common pattern is to automatically make all file descriptors they manage to O_NONBLOCK. For such libraries the EAGAIN error code is treated specially. When a function is called that returns EAGAIN the function isn't called again until the event loop indicates the the file descriptor is ready. Supporting EAGAIN when waiting on pidfds makes such libraries just work with little effort. In the following patch we will extend waitid() internally to support non-blocking pidfds. This introduces a new flag PIDFD_NONBLOCK that is equivalent to O_NONBLOCK. This follows the same patterns we have for other (anon inode) file descriptors such as EFD_NONBLOCK, IN_NONBLOCK, SFD_NONBLOCK, TFD_NONBLOCK and the same for close-on-exec flags. Suggested-by:

Josh Triplett <josh@joshtriplett.org> Signed-off-by:

Christian Brauner <christian.brauner@ubuntu.com> Reviewed-by:

Josh Triplett <josh@joshtriplett.org> Reviewed-by:

Oleg Nesterov <oleg@redhat.com> Cc: Kees Cook <keescook@chromium.org> Cc: Sargun Dhillon <sargun@sargun.me> Cc: Oleg Nesterov <oleg@redhat.com> Link: https://lore.kernel.org/lkml/20200811181236.GA18763@localhost/ Link: https://github.com/joshtriplett/async-pidfd Link: https://lore.kernel.org/r/20200902102130.147672-2-christian.brauner@ubuntu.com

include/uapi/linux/pidfd.h

0 → 100644

+12 −0

Original line number	Diff line number	Diff line
		/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */

		#ifndef _UAPI_LINUX_PIDFD_H
		#define _UAPI_LINUX_PIDFD_H

		#include <linux/types.h>
		#include <linux/fcntl.h>

		/* Flags for pidfd_open(). */
		#define PIDFD_NONBLOCK O_NONBLOCK

		#endif /* _UAPI_LINUX_PIDFD_H */

kernel/pid.c

+7 −5

Original line number	Diff line number	Diff line
		@@ -43,6 +43,7 @@
		#include <linux/sched/task.h>
		#include <linux/idr.h>
		#include <net/sock.h>
		#include <uapi/linux/pidfd.h>

		struct pid init_struct_pid = {
		.count = REFCOUNT_INIT(1),
		@@ -523,6 +524,7 @@ struct pid find_ge_pid(int nr, struct pid_namespace ns)
		* pidfd_create() - Create a new pid file descriptor.
		*
		* @pid: struct pid that the pidfd will reference
		* @flags: flags to pass
		*
		* This creates a new pid file descriptor with the O_CLOEXEC flag set.
		*
		@@ -532,12 +534,12 @@ struct pid find_ge_pid(int nr, struct pid_namespace ns)
		* Return: On success, a cloexec pidfd is returned.
		* On error, a negative errno number will be returned.
		*/
		static int pidfd_create(struct pid *pid)
		static int pidfd_create(struct pid *pid, unsigned int flags)
		{
		int fd;

		fd = anon_inode_getfd("[pidfd]", &pidfd_fops, get_pid(pid),
		O_RDWR \| O_CLOEXEC);
		flags \| O_RDWR \| O_CLOEXEC);
		if (fd < 0)
		put_pid(pid);

		@@ -565,7 +567,7 @@ SYSCALL_DEFINE2(pidfd_open, pid_t, pid, unsigned int, flags)
		int fd;
		struct pid *p;

		if (flags)
		if (flags & ~PIDFD_NONBLOCK)
		return -EINVAL;

		if (pid <= 0)
		@@ -576,7 +578,7 @@ SYSCALL_DEFINE2(pidfd_open, pid_t, pid, unsigned int, flags)
		return -ESRCH;

		if (pid_has_task(p, PIDTYPE_TGID))
		fd = pidfd_create(p);
		fd = pidfd_create(p, flags);
		else
		fd = -EINVAL;

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