ioprio.c

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/*
 * fs/ioprio.c
 *
 * Copyright (C) 2004 Jens Axboe <[email protected]>
 *
 * Helper functions for setting/querying io priorities of processes. The
 * system calls closely mimmick getpriority/setpriority, see the man page for
 * those. The prio argument is a composite of prio class and prio data, where
 * the data argument has meaning within that class. The standard scheduling
 * classes have 8 distinct prio levels, with 0 being the highest prio and 7
 * being the lowest.
 *
 * IOW, setting BE scheduling class with prio 2 is done ala:
 *
 * unsigned int prio = (IOPRIO_CLASS_BE << IOPRIO_CLASS_SHIFT) | 2;
 *
 * ioprio_set(PRIO_PROCESS, pid, prio);
 *
 * See also Documentation/block/ioprio.txt
 *
 */
#include <linux/gfp.h>
#include <linux/kernel.h>
#include <linux/export.h>
#include <linux/ioprio.h>
#include <linux/blkdev.h>
#include <linux/capability.h>
#include <linux/syscalls.h>
#include <linux/security.h>
#include <linux/pid_namespace.h>

int set_task_ioprio(struct task_struct *task, int ioprio)
{
    int err;
    struct io_context *ioc;
    const struct cred *cred = current_cred(), *tcred;

    rcu_read_lock();
    tcred = __task_cred(task);
    if (!uid_eq(tcred->uid, cred->euid) &&
        !uid_eq(tcred->uid, cred->uid) && !capable(CAP_SYS_NICE)) {
        rcu_read_unlock();
        return -EPERM;
    }
    rcu_read_unlock();

    err = security_task_setioprio(task, ioprio);
    if (err)
        return err;

    ioc = get_task_io_context(task, GFP_ATOMIC, NUMA_NO_NODE);
    if (ioc) {
        ioc->ioprio = ioprio;
        put_io_context(ioc);
    }

    return err;
}
EXPORT_SYMBOL_GPL(set_task_ioprio);

SYSCALL_DEFINE3(ioprio_set, int, which, int, who, int, ioprio)
{
    int class = IOPRIO_PRIO_CLASS(ioprio);
    int data = IOPRIO_PRIO_DATA(ioprio);
    struct task_struct *p, *g;
    struct user_struct *user;
    struct pid *pgrp;
    kuid_t uid;
    int ret;

    switch (class) {
        case IOPRIO_CLASS_RT:
            if (!capable(CAP_SYS_ADMIN))
                return -EPERM;
            /* fall through, rt has prio field too */
        case IOPRIO_CLASS_BE:
            if (data >= IOPRIO_BE_NR || data < 0)
                return -EINVAL;

            break;
        case IOPRIO_CLASS_IDLE:
            break;
        case IOPRIO_CLASS_NONE:
            if (data)
                return -EINVAL;
            break;
        default:
            return -EINVAL;
    }

    ret = -ESRCH;
    rcu_read_lock();
    switch (which) {
        case IOPRIO_WHO_PROCESS:
            if (!who)
                p = current;
            else
                p = find_task_by_vpid(who);
            if (p)
                ret = set_task_ioprio(p, ioprio);
            break;
        case IOPRIO_WHO_PGRP:
            if (!who)
                pgrp = task_pgrp(current);
            else
                pgrp = find_vpid(who);
            do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
                ret = set_task_ioprio(p, ioprio);
                if (ret)
                    break;
            } while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
            break;
        case IOPRIO_WHO_USER:
            uid = make_kuid(current_user_ns(), who);
            if (!uid_valid(uid))
                break;
            if (!who)
                user = current_user();
            else
                user = find_user(uid);

            if (!user)
                break;

            do_each_thread(g, p) {
                if (!uid_eq(task_uid(p), uid))
                    continue;
                ret = set_task_ioprio(p, ioprio);
                if (ret)
                    goto free_uid;
            } while_each_thread(g, p);
free_uid:
            if (who)
                free_uid(user);
            break;
        default:
            ret = -EINVAL;
    }

    rcu_read_unlock();
    return ret;
}

static int get_task_ioprio(struct task_struct *p)
{
    int ret;

    ret = security_task_getioprio(p);
    if (ret)
        goto out;
    ret = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_NONE, IOPRIO_NORM);
    if (p->io_context)
        ret = p->io_context->ioprio;
out:
    return ret;
}

int ioprio_best(unsigned short aprio, unsigned short bprio)
{
    unsigned short aclass = IOPRIO_PRIO_CLASS(aprio);
    unsigned short bclass = IOPRIO_PRIO_CLASS(bprio);

    if (aclass == IOPRIO_CLASS_NONE)
        aclass = IOPRIO_CLASS_BE;
    if (bclass == IOPRIO_CLASS_NONE)
        bclass = IOPRIO_CLASS_BE;

    if (aclass == bclass)
        return min(aprio, bprio);
    if (aclass > bclass)
        return bprio;
    else
        return aprio;
}

SYSCALL_DEFINE2(ioprio_get, int, which, int, who)
{
    struct task_struct *g, *p;
    struct user_struct *user;
    struct pid *pgrp;
    kuid_t uid;
    int ret = -ESRCH;
    int tmpio;

    rcu_read_lock();
    switch (which) {
        case IOPRIO_WHO_PROCESS:
            if (!who)
                p = current;
            else
                p = find_task_by_vpid(who);
            if (p)
                ret = get_task_ioprio(p);
            break;
        case IOPRIO_WHO_PGRP:
            if (!who)
                pgrp = task_pgrp(current);
            else
                pgrp = find_vpid(who);
            do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
                tmpio = get_task_ioprio(p);
                if (tmpio < 0)
                    continue;
                if (ret == -ESRCH)
                    ret = tmpio;
                else
                    ret = ioprio_best(ret, tmpio);
            } while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
            break;
        case IOPRIO_WHO_USER:
            uid = make_kuid(current_user_ns(), who);
            if (!who)
                user = current_user();
            else
                user = find_user(uid);

            if (!user)
                break;

            do_each_thread(g, p) {
                if (!uid_eq(task_uid(p), user->uid))
                    continue;
                tmpio = get_task_ioprio(p);
                if (tmpio < 0)
                    continue;
                if (ret == -ESRCH)
                    ret = tmpio;
                else
                    ret = ioprio_best(ret, tmpio);
            } while_each_thread(g, p);

            if (who)
                free_uid(user);
            break;
        default:
            ret = -EINVAL;
    }

    rcu_read_unlock();
    return ret;
}