systemd/src/shared/ioprio.h

#ifndef IOPRIO_H
#define IOPRIO_H

/* This is minimal version of Linux' linux/ioprio.h header file, which
 * is licensed GPL2 */

#include <unistd.h>
#include <sys/syscall.h>

/*
 * Gives us 8 prio classes with 13-bits of data for each class
 */
#define IOPRIO_BITS             (16)
#define IOPRIO_CLASS_SHIFT      (13)
#define IOPRIO_PRIO_MASK        ((1UL << IOPRIO_CLASS_SHIFT) - 1)

#define IOPRIO_PRIO_CLASS(mask) ((mask) >> IOPRIO_CLASS_SHIFT)
#define IOPRIO_PRIO_DATA(mask)  ((mask) & IOPRIO_PRIO_MASK)
#define IOPRIO_PRIO_VALUE(class, data)  (((class) << IOPRIO_CLASS_SHIFT) | data)

#define ioprio_valid(mask)      (IOPRIO_PRIO_CLASS((mask)) != IOPRIO_CLASS_NONE)

/*
 * These are the io priority groups as implemented by CFQ. RT is the realtime
 * class, it always gets premium service. BE is the best-effort scheduling
 * class, the default for any process. IDLE is the idle scheduling class, it
 * is only served when no one else is using the disk.
 */
enum {
        IOPRIO_CLASS_NONE,
        IOPRIO_CLASS_RT,
        IOPRIO_CLASS_BE,
        IOPRIO_CLASS_IDLE,
};

/*
 * 8 best effort priority levels are supported
 */
#define IOPRIO_BE_NR    (8)

enum {
        IOPRIO_WHO_PROCESS = 1,
        IOPRIO_WHO_PGRP,
        IOPRIO_WHO_USER,
};

static inline int ioprio_set(int which, int who, int ioprio) {
        return syscall(__NR_ioprio_set, which, who, ioprio);
}

static inline int ioprio_get(int which, int who) {
        return syscall(__NR_ioprio_get, which, who);
}

#endif