text: /*
   * fs/ioprio.c
   *
   * Copyright (C) 2004 Jens Axboe <axboe@kernel.dk>
   *
   * 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 (tcred->uid != cred->euid &&
  	    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_changed(ioc, 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;
  	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:
  			if (!who)
  				user = current_user();
  			else
  				user = find_user(who);
  
  			if (!user)
  				break;
  
  			do_each_thread(g, p) {
  				if (__task_cred(p)->uid != who)
  					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;
  	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:
  			if (!who)
  				user = current_user();
  			else
  				user = find_user(who);
  
  			if (!user)
  				break;
  
  			do_each_thread(g, p) {
  				if (__task_cred(p)->uid != 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;
  }
  