root/fs/proc/stat.c
// SPDX-License-Identifier: GPL-2.0
#include <linux/cpumask.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/interrupt.h>
#include <linux/kernel_stat.h>
#include <linux/proc_fs.h>
#include <linux/sched.h>
#include <linux/sched/stat.h>
#include <linux/seq_file.h>
#include <linux/slab.h>
#include <linux/time.h>
#include <linux/time_namespace.h>
#include <linux/irqnr.h>
#include <linux/sched/cputime.h>
#include <linux/tick.h>

#ifndef arch_irq_stat_cpu
#define arch_irq_stat_cpu(cpu) 0
#endif
#ifndef arch_irq_stat
#define arch_irq_stat() 0
#endif

u64 get_idle_time(struct kernel_cpustat *kcs, int cpu)
{
        u64 idle, idle_usecs = -1ULL;

        if (cpu_online(cpu))
                idle_usecs = get_cpu_idle_time_us(cpu, NULL);

        if (idle_usecs == -1ULL)
                /* !NO_HZ or cpu offline so we can rely on cpustat.idle */
                idle = kcs->cpustat[CPUTIME_IDLE];
        else
                idle = idle_usecs * NSEC_PER_USEC;

        return idle;
}

static u64 get_iowait_time(struct kernel_cpustat *kcs, int cpu)
{
        u64 iowait, iowait_usecs = -1ULL;

        if (cpu_online(cpu))
                iowait_usecs = get_cpu_iowait_time_us(cpu, NULL);

        if (iowait_usecs == -1ULL)
                /* !NO_HZ or cpu offline so we can rely on cpustat.iowait */
                iowait = kcs->cpustat[CPUTIME_IOWAIT];
        else
                iowait = iowait_usecs * NSEC_PER_USEC;

        return iowait;
}

static void show_irq_gap(struct seq_file *p, unsigned int gap)
{
        static const char zeros[] = " 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0";

        while (gap > 0) {
                unsigned int inc;

                inc = min_t(unsigned int, gap, ARRAY_SIZE(zeros) / 2);
                seq_write(p, zeros, 2 * inc);
                gap -= inc;
        }
}

static void show_all_irqs(struct seq_file *p)
{
        unsigned int i, next = 0;

        for_each_active_irq(i) {
                show_irq_gap(p, i - next);
                seq_put_decimal_ull(p, " ", kstat_irqs_usr(i));
                next = i + 1;
        }
        show_irq_gap(p, irq_get_nr_irqs() - next);
}

static int show_stat(struct seq_file *p, void *v)
{
        int i, j;
        u64 user, nice, system, idle, iowait, irq, softirq, steal;
        u64 guest, guest_nice;
        u64 sum = 0;
        u64 sum_softirq = 0;
        unsigned int per_softirq_sums[NR_SOFTIRQS] = {0};
        struct timespec64 boottime;

        user = nice = system = idle = iowait =
                irq = softirq = steal = 0;
        guest = guest_nice = 0;
        getboottime64(&boottime);
        /* shift boot timestamp according to the timens offset */
        timens_sub_boottime(&boottime);

        for_each_possible_cpu(i) {
                struct kernel_cpustat kcpustat;
                u64 *cpustat = kcpustat.cpustat;

                kcpustat_cpu_fetch(&kcpustat, i);

                user            += cpustat[CPUTIME_USER];
                nice            += cpustat[CPUTIME_NICE];
                system          += cpustat[CPUTIME_SYSTEM];
                idle            += get_idle_time(&kcpustat, i);
                iowait          += get_iowait_time(&kcpustat, i);
                irq             += cpustat[CPUTIME_IRQ];
                softirq         += cpustat[CPUTIME_SOFTIRQ];
                steal           += cpustat[CPUTIME_STEAL];
                guest           += cpustat[CPUTIME_GUEST];
                guest_nice      += cpustat[CPUTIME_GUEST_NICE];
                sum             += kstat_cpu_irqs_sum(i);
                sum             += arch_irq_stat_cpu(i);

                for (j = 0; j < NR_SOFTIRQS; j++) {
                        unsigned int softirq_stat = kstat_softirqs_cpu(j, i);

                        per_softirq_sums[j] += softirq_stat;
                        sum_softirq += softirq_stat;
                }
        }
        sum += arch_irq_stat();

        seq_put_decimal_ull(p, "cpu  ", nsec_to_clock_t(user));
        seq_put_decimal_ull(p, " ", nsec_to_clock_t(nice));
        seq_put_decimal_ull(p, " ", nsec_to_clock_t(system));
        seq_put_decimal_ull(p, " ", nsec_to_clock_t(idle));
        seq_put_decimal_ull(p, " ", nsec_to_clock_t(iowait));
        seq_put_decimal_ull(p, " ", nsec_to_clock_t(irq));
        seq_put_decimal_ull(p, " ", nsec_to_clock_t(softirq));
        seq_put_decimal_ull(p, " ", nsec_to_clock_t(steal));
        seq_put_decimal_ull(p, " ", nsec_to_clock_t(guest));
        seq_put_decimal_ull(p, " ", nsec_to_clock_t(guest_nice));
        seq_putc(p, '\n');

        for_each_online_cpu(i) {
                struct kernel_cpustat kcpustat;
                u64 *cpustat = kcpustat.cpustat;

                kcpustat_cpu_fetch(&kcpustat, i);

                /* Copy values here to work around gcc-2.95.3, gcc-2.96 */
                user            = cpustat[CPUTIME_USER];
                nice            = cpustat[CPUTIME_NICE];
                system          = cpustat[CPUTIME_SYSTEM];
                idle            = get_idle_time(&kcpustat, i);
                iowait          = get_iowait_time(&kcpustat, i);
                irq             = cpustat[CPUTIME_IRQ];
                softirq         = cpustat[CPUTIME_SOFTIRQ];
                steal           = cpustat[CPUTIME_STEAL];
                guest           = cpustat[CPUTIME_GUEST];
                guest_nice      = cpustat[CPUTIME_GUEST_NICE];
                seq_printf(p, "cpu%d", i);
                seq_put_decimal_ull(p, " ", nsec_to_clock_t(user));
                seq_put_decimal_ull(p, " ", nsec_to_clock_t(nice));
                seq_put_decimal_ull(p, " ", nsec_to_clock_t(system));
                seq_put_decimal_ull(p, " ", nsec_to_clock_t(idle));
                seq_put_decimal_ull(p, " ", nsec_to_clock_t(iowait));
                seq_put_decimal_ull(p, " ", nsec_to_clock_t(irq));
                seq_put_decimal_ull(p, " ", nsec_to_clock_t(softirq));
                seq_put_decimal_ull(p, " ", nsec_to_clock_t(steal));
                seq_put_decimal_ull(p, " ", nsec_to_clock_t(guest));
                seq_put_decimal_ull(p, " ", nsec_to_clock_t(guest_nice));
                seq_putc(p, '\n');
        }
        seq_put_decimal_ull(p, "intr ", (unsigned long long)sum);

        show_all_irqs(p);

        seq_printf(p,
                "\nctxt %llu\n"
                "btime %llu\n"
                "processes %lu\n"
                "procs_running %u\n"
                "procs_blocked %u\n",
                nr_context_switches(),
                (unsigned long long)boottime.tv_sec,
                total_forks,
                nr_running(),
                nr_iowait());

        seq_put_decimal_ull(p, "softirq ", (unsigned long long)sum_softirq);

        for (i = 0; i < NR_SOFTIRQS; i++)
                seq_put_decimal_ull(p, " ", per_softirq_sums[i]);
        seq_putc(p, '\n');

        return 0;
}

static int stat_open(struct inode *inode, struct file *file)
{
        unsigned int size = 1024 + 128 * num_online_cpus();

        /* minimum size to display an interrupt count : 2 bytes */
        size += 2 * irq_get_nr_irqs();
        return single_open_size(file, show_stat, NULL, size);
}

static const struct proc_ops stat_proc_ops = {
        .proc_flags     = PROC_ENTRY_PERMANENT,
        .proc_open      = stat_open,
        .proc_read_iter = seq_read_iter,
        .proc_lseek     = seq_lseek,
        .proc_release   = single_release,
};

static int __init proc_stat_init(void)
{
        proc_create("stat", 0, NULL, &stat_proc_ops);
        return 0;
}
fs_initcall(proc_stat_init);