ioctl_pipe - Man Page

#include <linux/watch_queue.h>  /* Definition of IOC_WATCH_QUEUE_* */
#include <sys/ioctl.h>

int ioctl(int pipefd[1], IOC_WATCH_QUEUE_SET_SIZE, int size);
int ioctl(int pipefd[1], IOC_WATCH_QUEUE_SET_FILTER,
          struct watch_notification_filter *filter);

The following ioctl(2) operations are provided to set up general notification queue parameters. The notification queue is built on the top of a pipe(2) opened with the O_NOTIFICATION_PIPE flag.

IOC_WATCH_QUEUE_SET_SIZE (since Linux 5.8)

Preallocates the pipe buffer memory so that it can fit size notification messages. Currently, size must be between 1 and 512.

IOC_WATCH_QUEUE_SET_FILTER (since Linux 5.8)

Watch queue filter can limit events that are received. Filters are passed in a struct watch_notification_filter and each filter is described by a struct watch_notification_type_filter structure.

struct watch_notification_filter {
        __u32   nr_filters;
        __u32   __reserved;
        struct watch_notification_type_filter filters[];
};

struct watch_notification_type_filter {
        __u32   type;
        __u32   info_filter;
        __u32   info_mask;
        __u32   subtype_filter[8];
};

pipe(2), ioctl(2)