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   1 /*
   2  * fs/ioprio.c
   3  *
   4  * Copyright (C) 2004 Jens Axboe <axboe@kernel.dk>
   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 #include <linux/capability.h>
  26 #include <linux/syscalls.h>
  27 #include <linux/security.h>
  28
  29 static int set_task_ioprio(struct task_struct *task, int ioprio)
  30 {
  31         int err;
  32         struct io_context *ioc;
  33
  34         if (task->uid != current->euid &&
  35             task->uid != current->uid && !capable(CAP_SYS_NICE))
  36                 return -EPERM;
  37
  38         err = security_task_setioprio(task, ioprio);
  39         if (err)
  40                 return err;
  41
  42         task_lock(task);
  43
  44         task->ioprio = ioprio;
  45
  46         ioc = task->io_context;
  47         /* see wmb() in current_io_context() */
  48         smp_read_barrier_depends();
  49
  50         if (ioc)
  51                 ioc->ioprio_changed = 1;
  52
  53         task_unlock(task);
  54         return 0;
  55 }
  56
  57 asmlinkage long sys_ioprio_set(int which, int who, int ioprio)
  58 {
  59         int class = IOPRIO_PRIO_CLASS(ioprio);
  60         int data = IOPRIO_PRIO_DATA(ioprio);
  61         struct task_struct *p, *g;
  62         struct user_struct *user;
  63         int ret;
  64
  65         switch (class) {
  66                 case IOPRIO_CLASS_RT:
  67                         if (!capable(CAP_SYS_ADMIN))
  68                                 return -EPERM;
  69                         /* fall through, rt has prio field too */
  70                 case IOPRIO_CLASS_BE:
  71                         if (data >= IOPRIO_BE_NR || data < 0)
  72                                 return -EINVAL;
  73
  74                         break;
  75                 case IOPRIO_CLASS_IDLE:
  76                         if (!capable(CAP_SYS_ADMIN))
  77                                 return -EPERM;
  78                         break;
  79                 default:
  80                         return -EINVAL;
  81         }
  82
  83         ret = -ESRCH;
  84         /*
  85          * We want IOPRIO_WHO_PGRP/IOPRIO_WHO_USER to be "atomic",
  86          * so we can't use rcu_read_lock(). See re-copy of ->ioprio
  87          * in copy_process().
  88          */
  89         read_lock(&tasklist_lock);
  90         switch (which) {
  91                 case IOPRIO_WHO_PROCESS:
  92                         if (!who)
  93                                 p = current;
  94                         else
  95                                 p = find_task_by_pid(who);
  96                         if (p)
  97                                 ret = set_task_ioprio(p, ioprio);
  98                         break;
  99                 case IOPRIO_WHO_PGRP:
 100                         if (!who)
 101                                 who = process_group(current);
 102                         do_each_task_pid(who, PIDTYPE_PGID, p) {
 103                                 ret = set_task_ioprio(p, ioprio);
 104                                 if (ret)
 105                                         break;
 106                         } while_each_task_pid(who, PIDTYPE_PGID, p);
 107                         break;
 108                 case IOPRIO_WHO_USER:
 109                         if (!who)
 110                                 user = current->user;
 111                         else
 112                                 user = find_user(who);
 113
 114                         if (!user)
 115                                 break;
 116
 117                         do_each_thread(g, p) {
 118                                 if (p->uid != who)
 119                                         continue;
 120                                 ret = set_task_ioprio(p, ioprio);
 121                                 if (ret)
 122                                         goto free_uid;
 123                         } while_each_thread(g, p);
 124 free_uid:
 125                         if (who)
 126                                 free_uid(user);
 127                         break;
 128                 default:
 129                         ret = -EINVAL;
 130         }
 131
 132         read_unlock(&tasklist_lock);
 133         return ret;
 134 }
 135
 136 static int get_task_ioprio(struct task_struct *p)
 137 {
 138         int ret;
 139
 140         ret = security_task_getioprio(p);
 141         if (ret)
 142                 goto out;
 143         ret = p->ioprio;
 144 out:
 145         return ret;
 146 }
 147
 148 int ioprio_best(unsigned short aprio, unsigned short bprio)
 149 {
 150         unsigned short aclass = IOPRIO_PRIO_CLASS(aprio);
 151         unsigned short bclass = IOPRIO_PRIO_CLASS(bprio);
 152
 153         if (aclass == IOPRIO_CLASS_NONE)
 154                 aclass = IOPRIO_CLASS_BE;
 155         if (bclass == IOPRIO_CLASS_NONE)
 156                 bclass = IOPRIO_CLASS_BE;
 157
 158         if (aclass == bclass)
 159                 return min(aprio, bprio);
 160         if (aclass > bclass)
 161                 return bprio;
 162         else
 163                 return aprio;
 164 }
 165
 166 asmlinkage long sys_ioprio_get(int which, int who)
 167 {
 168         struct task_struct *g, *p;
 169         struct user_struct *user;
 170         int ret = -ESRCH;
 171         int tmpio;
 172
 173         read_lock(&tasklist_lock);
 174         switch (which) {
 175                 case IOPRIO_WHO_PROCESS:
 176                         if (!who)
 177                                 p = current;
 178                         else
 179                                 p = find_task_by_pid(who);
 180                         if (p)
 181                                 ret = get_task_ioprio(p);
 182                         break;
 183                 case IOPRIO_WHO_PGRP:
 184                         if (!who)
 185                                 who = process_group(current);
 186                         do_each_task_pid(who, PIDTYPE_PGID, p) {
 187                                 tmpio = get_task_ioprio(p);
 188                                 if (tmpio < 0)
 189                                         continue;
 190                                 if (ret == -ESRCH)
 191                                         ret = tmpio;
 192                                 else
 193                                         ret = ioprio_best(ret, tmpio);
 194                         } while_each_task_pid(who, PIDTYPE_PGID, p);
 195                         break;
 196                 case IOPRIO_WHO_USER:
 197                         if (!who)
 198                                 user = current->user;
 199                         else
 200                                 user = find_user(who);
 201
 202                         if (!user)
 203                                 break;
 204
 205                         do_each_thread(g, p) {
 206                                 if (p->uid != user->uid)
 207                                         continue;
 208                                 tmpio = get_task_ioprio(p);
 209                                 if (tmpio < 0)
 210                                         continue;
 211                                 if (ret == -ESRCH)
 212                                         ret = tmpio;
 213                                 else
 214                                         ret = ioprio_best(ret, tmpio);
 215                         } while_each_thread(g, p);
 216
 217                         if (who)
 218                                 free_uid(user);
 219                         break;
 220                 default:
 221                         ret = -EINVAL;
 222         }
 223
 224         read_unlock(&tasklist_lock);
 225         return ret;
 226 }
 227