/*
   * 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/kernel.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;

  	task_lock(task);

  	do {
  		ioc = task->io_context;
  		/* see wmb() in current_io_context() */
  		smp_read_barrier_depends();
  		if (ioc)
  			break;

  		ioc = alloc_io_context(GFP_ATOMIC, -1);
  		if (!ioc) {
  			err = -ENOMEM;
  			break;
  		}
  		task->io_context = ioc;

  	} while (1);

  	if (!err) {
  		ioc->ioprio = ioprio;

  		ioc->ioprio_changed = 1;

  	}

  
  	task_unlock(task);

  	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;

  	/*
  	 * We want IOPRIO_WHO_PGRP/IOPRIO_WHO_USER to be "atomic",
  	 * so we can't use rcu_read_lock(). See re-copy of ->ioprio
  	 * in copy_process().
  	 */
  	read_lock(&tasklist_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;
  	}

  	read_unlock(&tasklist_lock);

  	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;

  	read_lock(&tasklist_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;
  	}

  	read_unlock(&tasklist_lock);

  	return ret;
  }