fs/ioprio.c

   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 #include <linux/pid_namespace.h>
  29
  30 static int set_task_ioprio(struct task_struct *task, int ioprio)
  31 {
  32         int err;
  33         struct io_context *ioc;
  34
  35         if (task->uid != current->euid &&
  36             task->uid != current->uid && !capable(CAP_SYS_NICE))
  37                 return -EPERM;
  38
  39         err = security_task_setioprio(task, ioprio);
  40         if (err)
  41                 return err;
  42
  43         task_lock(task);
  44
  45         task->ioprio = ioprio;
  46
  47         ioc = task->io_context;
  48         /* see wmb() in current_io_context() */
  49         smp_read_barrier_depends();
  50
  51         if (ioc)
  52                 ioc->ioprio_changed = 1;
  53
  54         task_unlock(task);
  55         return 0;
  56 }
  57
  58 asmlinkage long sys_ioprio_set(int which, int who, int ioprio)
  59 {
  60         int class = IOPRIO_PRIO_CLASS(ioprio);
  61         int data = IOPRIO_PRIO_DATA(ioprio);
  62         struct task_struct *p, *g;
  63         struct user_struct *user;
  64         struct pid *pgrp;
  65         int ret;
  66
  67         switch (class) {
  68                 case IOPRIO_CLASS_RT:
  69                         if (!capable(CAP_SYS_ADMIN))
  70                                 return -EPERM;
  71                         /* fall through, rt has prio field too */
  72                 case IOPRIO_CLASS_BE:
  73                         if (data >= IOPRIO_BE_NR || data < 0)
  74                                 return -EINVAL;
  75
  76                         break;
  77                 case IOPRIO_CLASS_IDLE:
  78                         if (!capable(CAP_SYS_ADMIN))
  79                                 return -EPERM;
  80                         break;
  81                 case IOPRIO_CLASS_NONE:
  82                         if (data)
  83                                 return -EINVAL;
  84                         break;
  85                 default:
  86                         return -EINVAL;
  87         }
  88
  89         ret = -ESRCH;
  90         /*
  91          * We want IOPRIO_WHO_PGRP/IOPRIO_WHO_USER to be "atomic",
  92          * so we can't use rcu_read_lock(). See re-copy of ->ioprio
  93          * in copy_process().
  94          */
  95         read_lock(&tasklist_lock);
  96         switch (which) {
  97                 case IOPRIO_WHO_PROCESS:
  98                         if (!who)
  99                                 p = current;
 100                         else
 101                                 p = find_task_by_vpid(who);
 102                         if (p)
 103                                 ret = set_task_ioprio(p, ioprio);
 104                         break;
 105                 case IOPRIO_WHO_PGRP:
 106                         if (!who)
 107                                 pgrp = task_pgrp(current);
 108                         else
 109                                 pgrp = find_vpid(who);
 110                         do_each_pid_task(pgrp, PIDTYPE_PGID, p) {
 111                                 ret = set_task_ioprio(p, ioprio);
 112                                 if (ret)
 113                                         break;
 114                         } while_each_pid_task(pgrp, PIDTYPE_PGID, p);
 115                         break;
 116                 case IOPRIO_WHO_USER:
 117                         if (!who)
 118                                 user = current->user;
 119                         else
 120                                 user = find_user(who);
 121
 122                         if (!user)
 123                                 break;
 124
 125                         do_each_thread(g, p) {
 126                                 if (p->uid != who)
 127                                         continue;
 128                                 ret = set_task_ioprio(p, ioprio);
 129                                 if (ret)
 130                                         goto free_uid;
 131                         } while_each_thread(g, p);
 132 free_uid:
 133                         if (who)
 134                                 free_uid(user);
 135                         break;
 136                 default:
 137                         ret = -EINVAL;
 138         }
 139
 140         read_unlock(&tasklist_lock);
 141         return ret;
 142 }
 143
 144 static int get_task_ioprio(struct task_struct *p)
 145 {
 146         int ret;
 147
 148         ret = security_task_getioprio(p);
 149         if (ret)
 150                 goto out;
 151         ret = p->ioprio;
 152 out:
 153         return ret;
 154 }
 155
 156 int ioprio_best(unsigned short aprio, unsigned short bprio)
 157 {
 158         unsigned short aclass = IOPRIO_PRIO_CLASS(aprio);
 159         unsigned short bclass = IOPRIO_PRIO_CLASS(bprio);
 160
 161         if (aclass == IOPRIO_CLASS_NONE)
 162                 aclass = IOPRIO_CLASS_BE;
 163         if (bclass == IOPRIO_CLASS_NONE)
 164                 bclass = IOPRIO_CLASS_BE;
 165
 166         if (aclass == bclass)
 167                 return min(aprio, bprio);
 168         if (aclass > bclass)
 169                 return bprio;
 170         else
 171                 return aprio;
 172 }
 173
 174 asmlinkage long sys_ioprio_get(int which, int who)
 175 {
 176         struct task_struct *g, *p;
 177         struct user_struct *user;
 178         struct pid *pgrp;
 179         int ret = -ESRCH;
 180         int tmpio;
 181
 182         read_lock(&tasklist_lock);
 183         switch (which) {
 184                 case IOPRIO_WHO_PROCESS:
 185                         if (!who)
 186                                 p = current;
 187                         else
 188                                 p = find_task_by_vpid(who);
 189                         if (p)
 190                                 ret = get_task_ioprio(p);
 191                         break;
 192                 case IOPRIO_WHO_PGRP:
 193                         if (!who)
 194                                 pgrp = task_pgrp(current);
 195                         else
 196                                 pgrp = find_vpid(who);
 197                         do_each_pid_task(pgrp, PIDTYPE_PGID, p) {
 198                                 tmpio = get_task_ioprio(p);
 199                                 if (tmpio < 0)
 200                                         continue;
 201                                 if (ret == -ESRCH)
 202                                         ret = tmpio;
 203                                 else
 204                                         ret = ioprio_best(ret, tmpio);
 205                         } while_each_pid_task(pgrp, PIDTYPE_PGID, p);
 206                         break;
 207                 case IOPRIO_WHO_USER:
 208                         if (!who)
 209                                 user = current->user;
 210                         else
 211                                 user = find_user(who);
 212
 213                         if (!user)
 214                                 break;
 215
 216                         do_each_thread(g, p) {
 217                                 if (p->uid != user->uid)
 218                                         continue;
 219                                 tmpio = get_task_ioprio(p);
 220                                 if (tmpio < 0)
 221                                         continue;
 222                                 if (ret == -ESRCH)
 223                                         ret = tmpio;
 224                                 else
 225                                         ret = ioprio_best(ret, tmpio);
 226                         } while_each_thread(g, p);
 227
 228                         if (who)
 229                                 free_uid(user);
 230                         break;
 231                 default:
 232                         ret = -EINVAL;
 233         }
 234
 235         read_unlock(&tasklist_lock);
 236         return ret;
 237 }
 238