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   1 /*
   2  * fs/ioprio.c
   3  *
   4  * Copyright (C) 2004 Jens Axboe <axboe@suse.de>
   5  *
   6  * Helper functions for setting/querying io priorities of processes. The
   7  * system calls closely mimmick getpriority/setpriority, see the man page for
   8  * those. The prio argument is a composite of prio class and prio data, where
   9  * the data argument has meaning within that class. The standard scheduling
  10  * classes have 8 distinct prio levels, with 0 being the highest prio and 7
  11  * being the lowest.
  12  *
  13  * IOW, setting BE scheduling class with prio 2 is done ala:
  14  *
  15  * unsigned int prio = (IOPRIO_CLASS_BE << IOPRIO_CLASS_SHIFT) | 2;
  16  *
  17  * ioprio_set(PRIO_PROCESS, pid, prio);
  18  *
  19  * See also Documentation/block/ioprio.txt
  20  *
  21  */
  22 #include <linux/kernel.h>
  23 #include <linux/ioprio.h>
  24 #include <linux/blkdev.h>
  25
  26 static int set_task_ioprio(struct task_struct *task, int ioprio)
  27 {
  28         struct io_context *ioc;
  29
  30         if (task->uid != current->euid &&
  31             task->uid != current->uid && !capable(CAP_SYS_NICE))
  32                 return -EPERM;
  33
  34         task_lock(task);
  35
  36         task->ioprio = ioprio;
  37
  38         ioc = task->io_context;
  39         if (ioc && ioc->set_ioprio)
  40                 ioc->set_ioprio(ioc, ioprio);
  41
  42         task_unlock(task);
  43         return 0;
  44 }
  45
  46 asmlinkage int sys_ioprio_set(int which, int who, int ioprio)
  47 {
  48         int class = IOPRIO_PRIO_CLASS(ioprio);
  49         int data = IOPRIO_PRIO_DATA(ioprio);
  50         struct task_struct *p, *g;
  51         struct user_struct *user;
  52         int ret;
  53
  54         switch (class) {
  55                 case IOPRIO_CLASS_RT:
  56                         if (!capable(CAP_SYS_ADMIN))
  57                                 return -EPERM;
  58                         /* fall through, rt has prio field too */
  59                 case IOPRIO_CLASS_BE:
  60                         if (data >= IOPRIO_BE_NR || data < 0)
  61                                 return -EINVAL;
  62
  63                         break;
  64                 case IOPRIO_CLASS_IDLE:
  65                         break;
  66                 default:
  67                         return -EINVAL;
  68         }
  69
  70         ret = -ESRCH;
  71         read_lock_irq(&tasklist_lock);
  72         switch (which) {
  73                 case IOPRIO_WHO_PROCESS:
  74                         if (!who)
  75                                 p = current;
  76                         else
  77                                 p = find_task_by_pid(who);
  78                         if (p)
  79                                 ret = set_task_ioprio(p, ioprio);
  80                         break;
  81                 case IOPRIO_WHO_PGRP:
  82                         if (!who)
  83                                 who = process_group(current);
  84                         do_each_task_pid(who, PIDTYPE_PGID, p) {
  85                                 ret = set_task_ioprio(p, ioprio);
  86                                 if (ret)
  87                                         break;
  88                         } while_each_task_pid(who, PIDTYPE_PGID, p);
  89                         break;
  90                 case IOPRIO_WHO_USER:
  91                         if (!who)
  92                                 user = current->user;
  93                         else
  94                                 user = find_user(who);
  95
  96                         if (!user)
  97                                 break;
  98
  99                         do_each_thread(g, p) {
 100                                 if (p->uid != who)
 101                                         continue;
 102                                 ret = set_task_ioprio(p, ioprio);
 103                                 if (ret)
 104                                         break;
 105                         } while_each_thread(g, p);
 106
 107                         if (who)
 108                                 free_uid(user);
 109                         break;
 110                 default:
 111                         ret = -EINVAL;
 112         }
 113
 114         read_unlock_irq(&tasklist_lock);
 115         return ret;
 116 }
 117
 118 asmlinkage int sys_ioprio_get(int which, int who)
 119 {
 120         struct task_struct *g, *p;
 121         struct user_struct *user;
 122         int ret = -ESRCH;
 123
 124         read_lock_irq(&tasklist_lock);
 125         switch (which) {
 126                 case IOPRIO_WHO_PROCESS:
 127                         if (!who)
 128                                 p = current;
 129                         else
 130                                 p = find_task_by_pid(who);
 131                         if (p)
 132                                 ret = p->ioprio;
 133                         break;
 134                 case IOPRIO_WHO_PGRP:
 135                         if (!who)
 136                                 who = process_group(current);
 137                         do_each_task_pid(who, PIDTYPE_PGID, p) {
 138                                 if (ret == -ESRCH)
 139                                         ret = p->ioprio;
 140                                 else
 141                                         ret = ioprio_best(ret, p->ioprio);
 142                         } while_each_task_pid(who, PIDTYPE_PGID, p);
 143                         break;
 144                 case IOPRIO_WHO_USER:
 145                         if (!who)
 146                                 user = current->user;
 147                         else
 148                                 user = find_user(who);
 149
 150                         if (!user)
 151                                 break;
 152
 153                         do_each_thread(g, p) {
 154                                 if (p->uid != user->uid)
 155                                         continue;
 156                                 if (ret == -ESRCH)
 157                                         ret = p->ioprio;
 158                                 else
 159                                         ret = ioprio_best(ret, p->ioprio);
 160                         } while_each_thread(g, p);
 161
 162                         if (who)
 163                                 free_uid(user);
 164                         break;
 165                 default:
 166                         ret = -EINVAL;
 167         }
 168
 169         read_unlock_irq(&tasklist_lock);
 170         return ret;
 171 }
 172