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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         struct pid *pgrp;
  64         int ret;
  65
  66         switch (class) {
  67                 case IOPRIO_CLASS_RT:
  68                         if (!capable(CAP_SYS_ADMIN))
  69                                 return -EPERM;
  70                         /* fall through, rt has prio field too */
  71                 case IOPRIO_CLASS_BE:
  72                         if (data >= IOPRIO_BE_NR || data < 0)
  73                                 return -EINVAL;
  74
  75                         break;
  76                 case IOPRIO_CLASS_IDLE:
  77                         if (!capable(CAP_SYS_ADMIN))
  78                                 return -EPERM;
  79                         break;
  80                 default:
  81                         return -EINVAL;
  82         }
  83
  84         ret = -ESRCH;
  85         /*
  86          * We want IOPRIO_WHO_PGRP/IOPRIO_WHO_USER to be "atomic",
  87          * so we can't use rcu_read_lock(). See re-copy of ->ioprio
  88          * in copy_process().
  89          */
  90         read_lock(&tasklist_lock);
  91         switch (which) {
  92                 case IOPRIO_WHO_PROCESS:
  93                         if (!who)
  94                                 p = current;
  95                         else
  96                                 p = find_task_by_pid(who);
  97                         if (p)
  98                                 ret = set_task_ioprio(p, ioprio);
  99                         break;
 100                 case IOPRIO_WHO_PGRP:
 101                         if (!who)
 102                                 pgrp = task_pgrp(current);
 103                         else
 104                                 pgrp = find_pid(who);
 105                         do_each_pid_task(pgrp, PIDTYPE_PGID, p) {
 106                                 ret = set_task_ioprio(p, ioprio);
 107                                 if (ret)
 108                                         break;
 109                         } while_each_pid_task(pgrp, PIDTYPE_PGID, p);
 110                         break;
 111                 case IOPRIO_WHO_USER:
 112                         if (!who)
 113                                 user = current->user;
 114                         else
 115                                 user = find_user(who);
 116
 117                         if (!user)
 118                                 break;
 119
 120                         do_each_thread(g, p) {
 121                                 if (p->uid != who)
 122                                         continue;
 123                                 ret = set_task_ioprio(p, ioprio);
 124                                 if (ret)
 125                                         goto free_uid;
 126                         } while_each_thread(g, p);
 127 free_uid:
 128                         if (who)
 129                                 free_uid(user);
 130                         break;
 131                 default:
 132                         ret = -EINVAL;
 133         }
 134
 135         read_unlock(&tasklist_lock);
 136         return ret;
 137 }
 138
 139 static int get_task_ioprio(struct task_struct *p)
 140 {
 141         int ret;
 142
 143         ret = security_task_getioprio(p);
 144         if (ret)
 145                 goto out;
 146         ret = p->ioprio;
 147 out:
 148         return ret;
 149 }
 150
 151 int ioprio_best(unsigned short aprio, unsigned short bprio)
 152 {
 153         unsigned short aclass = IOPRIO_PRIO_CLASS(aprio);
 154         unsigned short bclass = IOPRIO_PRIO_CLASS(bprio);
 155
 156         if (aclass == IOPRIO_CLASS_NONE)
 157                 aclass = IOPRIO_CLASS_BE;
 158         if (bclass == IOPRIO_CLASS_NONE)
 159                 bclass = IOPRIO_CLASS_BE;
 160
 161         if (aclass == bclass)
 162                 return min(aprio, bprio);
 163         if (aclass > bclass)
 164                 return bprio;
 165         else
 166                 return aprio;
 167 }
 168
 169 asmlinkage long sys_ioprio_get(int which, int who)
 170 {
 171         struct task_struct *g, *p;
 172         struct user_struct *user;
 173         struct pid *pgrp;
 174         int ret = -ESRCH;
 175         int tmpio;
 176
 177         read_lock(&tasklist_lock);
 178         switch (which) {
 179                 case IOPRIO_WHO_PROCESS:
 180                         if (!who)
 181                                 p = current;
 182                         else
 183                                 p = find_task_by_pid(who);
 184                         if (p)
 185                                 ret = get_task_ioprio(p);
 186                         break;
 187                 case IOPRIO_WHO_PGRP:
 188                         if (!who)
 189                                 pgrp = task_pgrp(current);
 190                         else
 191                                 pgrp = find_pid(who);
 192                         do_each_pid_task(pgrp, PIDTYPE_PGID, p) {
 193                                 tmpio = get_task_ioprio(p);
 194                                 if (tmpio < 0)
 195                                         continue;
 196                                 if (ret == -ESRCH)
 197                                         ret = tmpio;
 198                                 else
 199                                         ret = ioprio_best(ret, tmpio);
 200                         } while_each_pid_task(pgrp, PIDTYPE_PGID, p);
 201                         break;
 202                 case IOPRIO_WHO_USER:
 203                         if (!who)
 204                                 user = current->user;
 205                         else
 206                                 user = find_user(who);
 207
 208                         if (!user)
 209                                 break;
 210
 211                         do_each_thread(g, p) {
 212                                 if (p->uid != user->uid)
 213                                         continue;
 214                                 tmpio = get_task_ioprio(p);
 215                                 if (tmpio < 0)
 216                                         continue;
 217                                 if (ret == -ESRCH)
 218                                         ret = tmpio;
 219                                 else
 220                                         ret = ioprio_best(ret, tmpio);
 221                         } while_each_thread(g, p);
 222
 223                         if (who)
 224                                 free_uid(user);
 225                         break;
 226                 default:
 227                         ret = -EINVAL;
 228         }
 229
 230         read_unlock(&tasklist_lock);
 231         return ret;
 232 }
 233