uptime.c

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#include <linux/fs.h>
#include <linux/init.h>
#include <linux/proc_fs.h>
#include <linux/sched.h>
#include <linux/seq_file.h>
#include <linux/time.h>
#include <linux/kernel_stat.h>
#include <asm/cputime.h>

static int uptime_proc_show(struct seq_file *m, void *v)
{
    struct timespec uptime;
    struct timespec idle;
    u64 idletime;
    u64 nsec;
    u32 rem;
    int i;

    idletime = 0;
    for_each_possible_cpu(i)
        idletime += (__force u64) kcpustat_cpu(i).cpustat[CPUTIME_IDLE];

    do_posix_clock_monotonic_gettime(&uptime);
    monotonic_to_bootbased(&uptime);
    nsec = cputime64_to_jiffies64(idletime) * TICK_NSEC;
    idle.tv_sec = div_u64_rem(nsec, NSEC_PER_SEC, &rem);
    idle.tv_nsec = rem;
    seq_printf(m, "%lu.%02lu %lu.%02lu\n",
            (unsigned long) uptime.tv_sec,
            (uptime.tv_nsec / (NSEC_PER_SEC / 100)),
            (unsigned long) idle.tv_sec,
            (idle.tv_nsec / (NSEC_PER_SEC / 100)));
    return 0;
}

static int uptime_proc_open(struct inode *inode, struct file *file)
{
    return single_open(file, uptime_proc_show, NULL);
}

static const struct file_operations uptime_proc_fops = {
    .open       = uptime_proc_open,
    .read       = seq_read,
    .llseek     = seq_lseek,
    .release    = single_release,
};

static int __init proc_uptime_init(void)
{
    proc_create("uptime", 0, NULL, &uptime_proc_fops);
    return 0;
}
module_init(proc_uptime_init);