linux-imx

// SPDX-License-Identifier: GPL-2.0

/*

 * This file contains the procedures for the handling of select and poll

 *

 * Created for Linux based loosely upon Mathius Lattner's minix

 * patches by Peter MacDonald. Heavily edited by Linus.

 *

 *  4 February 1994

 *     COFF/ELF binary emulation. If the process has the STICKY_TIMEOUTS

 *     flag set in its personality we do *not* modify the given timeout

 *     parameter to reflect time remaining.

 *

 *  24 January 2000

 *     Changed sys_poll()/do_poll() to use PAGE_SIZE chunk-based allocation 

 *     of fds to overcome nfds < 16390 descriptors limit (Tigran Aivazian).

 */

​

#include <linux/kernel.h>

#include <linux/sched/signal.h>

#include <linux/sched/rt.h>

#include <linux/syscalls.h>

#include <linux/export.h>

#include <linux/slab.h>

#include <linux/poll.h>

#include <linux/personality.h> /* for STICKY_TIMEOUTS */

#include <linux/file.h>

#include <linux/fdtable.h>

#include <linux/fs.h>

#include <linux/rcupdate.h>

#include <linux/hrtimer.h>

#include <linux/freezer.h>

#include <net/busy_poll.h>

#include <linux/vmalloc.h>

​

#include <linux/uaccess.h>

​

​

/*

 * Estimate expected accuracy in ns from a timeval.

 *

 * After quite a bit of churning around, we've settled on

 * a simple thing of taking 0.1% of the timeout as the

 * slack, with a cap of 100 msec.

 * "nice" tasks get a 0.5% slack instead.

 *

 * Consider this comment an open invitation to come up with even

 * better solutions..

 */

​

#define MAX_SLACK   (100 * NSEC_PER_MSEC)

​

static long __estimate_accuracy(struct timespec64 *tv)

{

    long slack;

    int divfactor = 1000;

​

    if (tv->tv_sec < 0)

        return 0;

​

    if (task_nice(current) > 0)

        divfactor = divfactor / 5;

​

    if (tv->tv_sec > MAX_SLACK / (NSEC_PER_SEC/divfactor))

        return MAX_SLACK;

​

    slack = tv->tv_nsec / divfactor;

    slack += tv->tv_sec * (NSEC_PER_SEC/divfactor);

​

    if (slack > MAX_SLACK)

        return MAX_SLACK;

​

    return slack;

}

​

u64 select_estimate_accuracy(struct timespec64 *tv)

{

    u64 ret;

    struct timespec64 now;

​

    /*

     * Realtime tasks get a slack of 0 for obvious reasons.

     */

​

    if (rt_task(current))

        return 0;

​

    ktime_get_ts64(&now);

    now = timespec64_sub(*tv, now);

    ret = __estimate_accuracy(&now);

    if (ret < current->timer_slack_ns)

        return current->timer_slack_ns;

    return ret;