ioprio.c
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/*
* fs/ioprio.c
*
* Copyright (C) 2004 Jens Axboe <axboe@suse.de>
*
* 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/kernel.h>
#include <linux/ioprio.h>
#include <linux/blkdev.h>
#include <linux/capability.h>
#include <linux/syscalls.h>
static int set_task_ioprio(struct task_struct *task, int ioprio)
{
struct io_context *ioc;
if (task->uid != current->euid &&
task->uid != current->uid && !capable(CAP_SYS_NICE))
return -EPERM;
task_lock(task);
task->ioprio = ioprio;
ioc = task->io_context;
if (ioc && ioc->set_ioprio)
ioc->set_ioprio(ioc, ioprio);
task_unlock(task);
return 0;
}
asmlinkage long sys_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;
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:
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
break;
default:
return -EINVAL;
}
ret = -ESRCH;
read_lock_irq(&tasklist_lock);
switch (which) {
case IOPRIO_WHO_PROCESS:
if (!who)
p = current;
else
p = find_task_by_pid(who);
if (p)
ret = set_task_ioprio(p, ioprio);
break;
case IOPRIO_WHO_PGRP:
if (!who)
who = process_group(current);
do_each_task_pid(who, PIDTYPE_PGID, p) {
ret = set_task_ioprio(p, ioprio);
if (ret)
break;
} while_each_task_pid(who, PIDTYPE_PGID, p);
break;
case IOPRIO_WHO_USER:
if (!who)
user = current->user;
else
user = find_user(who);
if (!user)
break;
do_each_thread(g, p) {
if (p->uid != who)
continue;
ret = set_task_ioprio(p, ioprio);
if (ret)
break;
} while_each_thread(g, p);
if (who)
free_uid(user);
break;
default:
ret = -EINVAL;
}
read_unlock_irq(&tasklist_lock);
return ret;
}
asmlinkage long sys_ioprio_get(int which, int who)
{
struct task_struct *g, *p;
struct user_struct *user;
int ret = -ESRCH;
read_lock_irq(&tasklist_lock);
switch (which) {
case IOPRIO_WHO_PROCESS:
if (!who)
p = current;
else
p = find_task_by_pid(who);
if (p)
ret = p->ioprio;
break;
case IOPRIO_WHO_PGRP:
if (!who)
who = process_group(current);
do_each_task_pid(who, PIDTYPE_PGID, p) {
if (ret == -ESRCH)
ret = p->ioprio;
else
ret = ioprio_best(ret, p->ioprio);
} while_each_task_pid(who, PIDTYPE_PGID, p);
break;
case IOPRIO_WHO_USER:
if (!who)
user = current->user;
else
user = find_user(who);
if (!user)
break;
do_each_thread(g, p) {
if (p->uid != user->uid)
continue;
if (ret == -ESRCH)
ret = p->ioprio;
else
ret = ioprio_best(ret, p->ioprio);
} while_each_thread(g, p);
if (who)
free_uid(user);
break;
default:
ret = -EINVAL;
}
read_unlock_irq(&tasklist_lock);
return ret;
}