eventfd.h File Reference

Linux-compatible event notification file descriptor (<sys/eventfd.h>) More...

#include <zephyr/zvfs/eventfd.h>

Include dependency graph for eventfd.h:

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Macros
#define	EFD_SEMAPHORE   ZVFS_EFD_SEMAPHORE
	Semaphore-mode flag: each read decrements the counter by 1 instead of resetting to 0.
#define	EFD_NONBLOCK   ZVFS_EFD_NONBLOCK
	Non-blocking flag: reads and writes return EAGAIN instead of blocking.

Typedefs
typedef zvfs_eventfd_t	eventfd_t
	Counter value type for eventfd operations.

Functions
int	eventfd (unsigned int initval, int flags)
	Create a file descriptor for event notification.
int	eventfd_read (int fd, eventfd_t *value)
	Read the current counter value from an eventfd.
int	eventfd_write (int fd, eventfd_t value)
	Add a value to an eventfd counter.

Detailed Description

Linux-compatible event notification file descriptor (<sys/eventfd.h>)

eventfd provides a lightweight, kernel-managed counter that can be used for event notification between threads or between a kernel component and user space. It integrates with poll/select/epoll.

Note

eventfd is a Linux extension, not part of POSIX.1-2017, but is widely available on Linux and implemented here for compatibility.

Definition in file eventfd.h.

Macro Definition Documentation

EFD_NONBLOCK

#define EFD_NONBLOCK   ZVFS_EFD_NONBLOCK

Non-blocking flag: reads and writes return EAGAIN instead of blocking.

Definition at line 32 of file eventfd.h.

EFD_SEMAPHORE

#define EFD_SEMAPHORE   ZVFS_EFD_SEMAPHORE

Semaphore-mode flag: each read decrements the counter by 1 instead of resetting to 0.

Definition at line 30 of file eventfd.h.

Typedef Documentation

eventfd_t

typedef zvfs_eventfd_t eventfd_t

Counter value type for eventfd operations.

Definition at line 35 of file eventfd.h.

Function Documentation

eventfd()

int eventfd	(	unsigned int	initval,
		int	flags
	)

Create a file descriptor for event notification.

The returned file descriptor can be used with POSIX read()/write() or with eventfd_read()/eventfd_write(). It also integrates with poll(), allowing a writing thread to wake a polling thread simply by writing to the eventfd.

When using read()/write(), the buffer size must be exactly 8 bytes or the call will fail with EINVAL.

Parameters

initval	Initial counter value.
flags	0, EFD_SEMAPHORE, EFD_NONBLOCK, or their combination.

Returns

New eventfd file descriptor on success, -1 with errno set on failure.

See also

https://man7.org/linux/man-pages/man2/eventfd.2.html

eventfd_read()

int eventfd_read	(	int	fd,
		eventfd_t *	value
	)

Read the current counter value from an eventfd.

In normal mode the counter is reset to 0; in EFD_SEMAPHORE mode it is decremented by 1. Blocks if the counter is 0 (unless EFD_NONBLOCK).

Parameters

fd	Eventfd file descriptor.
value	Output: counter value read.

Returns

0 on success, -1 with errno set on failure.

See also

https://man7.org/linux/man-pages/man2/eventfd.2.html

eventfd_write()

int eventfd_write	(	int	fd,
		eventfd_t	value
	)

Add a value to an eventfd counter.

Wakes any thread blocked in eventfd_read(), read(), or poll() on fd.

Parameters

fd	Eventfd file descriptor.
value	Value to add to the counter.

Returns

0 on success, -1 with errno set on failure.

See also

https://man7.org/linux/man-pages/man2/eventfd.2.html