#include <linux/cgroup.h>
#include <linux/slab.h>
#include <linux/percpu.h>
#include <linux/spinlock.h>
#include <linux/cpumask.h>
#include <linux/seq_file.h>
#include <linux/rcupdate.h>
#include <linux/kernel_stat.h>
#include <linux/err.h>

#include "sched.h"

/*
 * CPU accounting code for task groups.
 *
 * Based on the work by Paul Menage (menage@google.com) and Balbir Singh
 * (balbir@in.ibm.com).
 */

/* Time spent by the tasks of the cpu accounting group executing in ... */
enum cpuacct_stat_index {
        CPUACCT_STAT_USER,      /* ... user mode */
        CPUACCT_STAT_SYSTEM,    /* ... kernel mode */

        CPUACCT_STAT_NSTATS,
};

/* track cpu usage of a group of tasks and its child groups */
struct cpuacct {
        struct cgroup_subsys_state css;
        /* cpuusage holds pointer to a u64-type object on every cpu */
        u64 __percpu *cpuusage;
        struct kernel_cpustat __percpu *cpustat;
};

static inline struct cpuacct *css_ca(struct cgroup_subsys_state *css)
{
        return css ? container_of(css, struct cpuacct, css) : NULL;
}

/* return cpu accounting group to which this task belongs */
static inline struct cpuacct *task_ca(struct task_struct *tsk)
{
        return css_ca(task_css(tsk, cpuacct_cgrp_id));
}

static inline struct cpuacct *parent_ca(struct cpuacct *ca)
{
        return css_ca(ca->css.parent);
}

static DEFINE_PER_CPU(u64, root_cpuacct_cpuusage);
static struct cpuacct root_cpuacct = {
        .cpustat        = &kernel_cpustat,
        .cpuusage       = &root_cpuacct_cpuusage,
};

/* create a new cpu accounting group */
static struct cgroup_subsys_state *
cpuacct_css_alloc(struct cgroup_subsys_state *parent_css)
{
        struct cpuacct *ca;

        if (!parent_css)
                return &root_cpuacct.css;

        ca = kzalloc(sizeof(*ca), GFP_KERNEL);
        if (!ca)
                goto out;

        ca->cpuusage = alloc_percpu(u64);
        if (!ca->cpuusage)
                goto out_free_ca;

        ca->cpustat = alloc_percpu(struct kernel_cpustat);
        if (!ca->cpustat)
                goto out_free_cpuusage;

        return &ca->css;

out_free_cpuusage:
        free_percpu(ca->cpuusage);
out_free_ca:
        kfree(ca);
out:
        return ERR_PTR(-ENOMEM);
}

/* destroy an existing cpu accounting group */
static void cpuacct_css_free(struct cgroup_subsys_state *css)
{
        struct cpuacct *ca = css_ca(css);

        free_percpu(ca->cpustat);
        free_percpu(ca->cpuusage);
        kfree(ca);
}

static u64 cpuacct_cpuusage_read(struct cpuacct *ca, int cpu)
{
        u64 *cpuusage = per_cpu_ptr(ca->cpuusage, cpu);
        u64 data;

#ifndef CONFIG_64BIT
        /*
         * Take rq->lock to make 64-bit read safe on 32-bit platforms.
         */
        raw_spin_lock_irq(&cpu_rq(cpu)->lock);
        data = *cpuusage;
        raw_spin_unlock_irq(&cpu_rq(cpu)->lock);
#else
        data = *cpuusage;
#endif

        return data;
}

static void cpuacct_cpuusage_write(struct cpuacct *ca, int cpu, u64 val)
{
        u64 *cpuusage = per_cpu_ptr(ca->cpuusage, cpu);

#ifndef CONFIG_64BIT
        /*
         * Take rq->lock to make 64-bit write safe on 32-bit platforms.
         */
        raw_spin_lock_irq(&cpu_rq(cpu)->lock);
        *cpuusage = val;
        raw_spin_unlock_irq(&cpu_rq(cpu)->lock);
#else
        *cpuusage = val;
#endif
}

/* return total cpu usage (in nanoseconds) of a group */
static u64 cpuusage_read(struct cgroup_subsys_state *css, struct cftype *cft)
{
        struct cpuacct *ca = css_ca(css);
        u64 totalcpuusage = 0;
        int i;

        for_each_present_cpu(i)
                totalcpuusage += cpuacct_cpuusage_read(ca, i);

        return totalcpuusage;
}

static int cpuusage_write(struct cgroup_subsys_state *css, struct cftype *cft,
                          u64 reset)
{
        struct cpuacct *ca = css_ca(css);
        int err = 0;
        int i;

        if (reset) {
                err = -EINVAL;
                goto out;
        }

        for_each_present_cpu(i)
                cpuacct_cpuusage_write(ca, i, 0);

out:
        return err;
}

static int cpuacct_percpu_seq_show(struct seq_file *m, void *V)
{
        struct cpuacct *ca = css_ca(seq_css(m));
        u64 percpu;
        int i;

        for_each_present_cpu(i) {
                percpu = cpuacct_cpuusage_read(ca, i);
                seq_printf(m, "%llu ", (unsigned long long) percpu);
        }
        seq_printf(m, "\n");
        return 0;
}

static const char * const cpuacct_stat_desc[] = {
        [CPUACCT_STAT_USER] = "user",
        [CPUACCT_STAT_SYSTEM] = "system",
};

static int cpuacct_stats_show(struct seq_file *sf, void *v)
{
        struct cpuacct *ca = css_ca(seq_css(sf));
        int cpu;
        s64 val = 0;

        for_each_online_cpu(cpu) {
                struct kernel_cpustat *kcpustat = per_cpu_ptr(ca->cpustat, cpu);
                val += kcpustat->cpustat[CPUTIME_USER];
                val += kcpustat->cpustat[CPUTIME_NICE];
        }
        val = cputime64_to_clock_t(val);
        seq_printf(sf, "%s %lld\n", cpuacct_stat_desc[CPUACCT_STAT_USER], val);

        val = 0;
        for_each_online_cpu(cpu) {
                struct kernel_cpustat *kcpustat = per_cpu_ptr(ca->cpustat, cpu);
                val += kcpustat->cpustat[CPUTIME_SYSTEM];
                val += kcpustat->cpustat[CPUTIME_IRQ];
                val += kcpustat->cpustat[CPUTIME_SOFTIRQ];
        }

        val = cputime64_to_clock_t(val);
        seq_printf(sf, "%s %lld\n", cpuacct_stat_desc[CPUACCT_STAT_SYSTEM], val);

        return 0;
}

static struct cftype files[] = {
        {
                .name = "usage",
                .read_u64 = cpuusage_read,
                .write_u64 = cpuusage_write,
        },
        {
                .name = "usage_percpu",
                .seq_show = cpuacct_percpu_seq_show,
        },
        {
                .name = "stat",
                .seq_show = cpuacct_stats_show,
        },
        { }     /* terminate */
};

/*
 * charge this task's execution time to its accounting group.
 *
 * called with rq->lock held.
 */
void cpuacct_charge(struct task_struct *tsk, u64 cputime)
{
        struct cpuacct *ca;
        int cpu;

        cpu = task_cpu(tsk);

        rcu_read_lock();

        ca = task_ca(tsk);

        while (true) {
                u64 *cpuusage = per_cpu_ptr(ca->cpuusage, cpu);
                *cpuusage += cputime;

                ca = parent_ca(ca);
                if (!ca)
                        break;
        }

        rcu_read_unlock();
}

/*
 * Add user/system time to cpuacct.
 *
 * Note: it's the caller that updates the account of the root cgroup.
 */
void cpuacct_account_field(struct task_struct *p, int index, u64 val)
{
        struct kernel_cpustat *kcpustat;
        struct cpuacct *ca;

        rcu_read_lock();
        ca = task_ca(p);
        while (ca != &root_cpuacct) {
                kcpustat = this_cpu_ptr(ca->cpustat);
                kcpustat->cpustat[index] += val;
                ca = parent_ca(ca);
        }
        rcu_read_unlock();
}

struct cgroup_subsys cpuacct_cgrp_subsys = {
        .css_alloc      = cpuacct_css_alloc,
        .css_free       = cpuacct_css_free,
        .legacy_cftypes = files,
        .early_init     = 1,
};