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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 #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         do {
  45                 ioc = task->io_context;
  46                 /* see wmb() in current_io_context() */
  47                 smp_read_barrier_depends();
  48                 if (ioc)
  49                         break;
  50
  51                 ioc = alloc_io_context(GFP_ATOMIC, -1);
  52                 if (!ioc) {
  53                         err = -ENOMEM;
  54                         break;
  55                 }
  56                 task->io_context = ioc;
  57                 ioc->task = task;
  58         } while (1);
  59
  60         if (!err) {
  61                 ioc->ioprio = ioprio;
  62                 ioc->ioprio_changed = 1;
  63         }
  64
  65         task_unlock(task);
  66         return err;
  67 }
  68
  69 asmlinkage long sys_ioprio_set(int which, int who, int ioprio)
  70 {
  71         int class = IOPRIO_PRIO_CLASS(ioprio);
  72         int data = IOPRIO_PRIO_DATA(ioprio);
  73         struct task_struct *p, *g;
  74         struct user_struct *user;
  75         struct pid *pgrp;
  76         int ret;
  77
  78         switch (class) {
  79                 case IOPRIO_CLASS_RT:
  80                         if (!capable(CAP_SYS_ADMIN))
  81                                 return -EPERM;
  82                         /* fall through, rt has prio field too */
  83                 case IOPRIO_CLASS_BE:
  84                         if (data >= IOPRIO_BE_NR || data < 0)
  85                                 return -EINVAL;
  86
  87                         break;
  88                 case IOPRIO_CLASS_IDLE:
  89                         if (!capable(CAP_SYS_ADMIN))
  90                                 return -EPERM;
  91                         break;
  92                 case IOPRIO_CLASS_NONE:
  93                         if (data)
  94                                 return -EINVAL;
  95                         break;
  96                 default:
  97                         return -EINVAL;
  98         }
  99
 100         ret = -ESRCH;
 101         /*
 102          * We want IOPRIO_WHO_PGRP/IOPRIO_WHO_USER to be "atomic",
 103          * so we can't use rcu_read_lock(). See re-copy of ->ioprio
 104          * in copy_process().
 105          */
 106         read_lock(&tasklist_lock);
 107         switch (which) {
 108                 case IOPRIO_WHO_PROCESS:
 109                         if (!who)
 110                                 p = current;
 111                         else
 112                                 p = find_task_by_vpid(who);
 113                         if (p)
 114                                 ret = set_task_ioprio(p, ioprio);
 115                         break;
 116                 case IOPRIO_WHO_PGRP:
 117                         if (!who)
 118                                 pgrp = task_pgrp(current);
 119                         else
 120                                 pgrp = find_vpid(who);
 121                         do_each_pid_task(pgrp, PIDTYPE_PGID, p) {
 122                                 ret = set_task_ioprio(p, ioprio);
 123                                 if (ret)
 124                                         break;
 125                         } while_each_pid_task(pgrp, PIDTYPE_PGID, p);
 126                         break;
 127                 case IOPRIO_WHO_USER:
 128                         if (!who)
 129                                 user = current->user;
 130                         else
 131                                 user = find_user(who);
 132
 133                         if (!user)
 134                                 break;
 135
 136                         do_each_thread(g, p) {
 137                                 if (p->uid != who)
 138                                         continue;
 139                                 ret = set_task_ioprio(p, ioprio);
 140                                 if (ret)
 141                                         goto free_uid;
 142                         } while_each_thread(g, p);
 143 free_uid:
 144                         if (who)
 145                                 free_uid(user);
 146                         break;
 147                 default:
 148                         ret = -EINVAL;
 149         }
 150
 151         read_unlock(&tasklist_lock);
 152         return ret;
 153 }
 154
 155 static int get_task_ioprio(struct task_struct *p)
 156 {
 157         int ret;
 158
 159         ret = security_task_getioprio(p);
 160         if (ret)
 161                 goto out;
 162         ret = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_NONE, IOPRIO_NORM);
 163         if (p->io_context)
 164                 ret = p->io_context->ioprio;
 165 out:
 166         return ret;
 167 }
 168
 169 int ioprio_best(unsigned short aprio, unsigned short bprio)
 170 {
 171         unsigned short aclass = IOPRIO_PRIO_CLASS(aprio);
 172         unsigned short bclass = IOPRIO_PRIO_CLASS(bprio);
 173
 174         if (aclass == IOPRIO_CLASS_NONE)
 175                 aclass = IOPRIO_CLASS_BE;
 176         if (bclass == IOPRIO_CLASS_NONE)
 177                 bclass = IOPRIO_CLASS_BE;
 178
 179         if (aclass == bclass)
 180                 return min(aprio, bprio);
 181         if (aclass > bclass)
 182                 return bprio;
 183         else
 184                 return aprio;
 185 }
 186
 187 asmlinkage long sys_ioprio_get(int which, int who)
 188 {
 189         struct task_struct *g, *p;
 190         struct user_struct *user;
 191         struct pid *pgrp;
 192         int ret = -ESRCH;
 193         int tmpio;
 194
 195         read_lock(&tasklist_lock);
 196         switch (which) {
 197                 case IOPRIO_WHO_PROCESS:
 198                         if (!who)
 199                                 p = current;
 200                         else
 201                                 p = find_task_by_vpid(who);
 202                         if (p)
 203                                 ret = get_task_ioprio(p);
 204                         break;
 205                 case IOPRIO_WHO_PGRP:
 206                         if (!who)
 207                                 pgrp = task_pgrp(current);
 208                         else
 209                                 pgrp = find_vpid(who);
 210                         do_each_pid_task(pgrp, PIDTYPE_PGID, p) {
 211                                 tmpio = get_task_ioprio(p);
 212                                 if (tmpio < 0)
 213                                         continue;
 214                                 if (ret == -ESRCH)
 215                                         ret = tmpio;
 216                                 else
 217                                         ret = ioprio_best(ret, tmpio);
 218                         } while_each_pid_task(pgrp, PIDTYPE_PGID, p);
 219                         break;
 220                 case IOPRIO_WHO_USER:
 221                         if (!who)
 222                                 user = current->user;
 223                         else
 224                                 user = find_user(who);
 225
 226                         if (!user)
 227                                 break;
 228
 229                         do_each_thread(g, p) {
 230                                 if (p->uid != user->uid)
 231                                         continue;
 232                                 tmpio = get_task_ioprio(p);
 233                                 if (tmpio < 0)
 234                                         continue;
 235                                 if (ret == -ESRCH)
 236                                         ret = tmpio;
 237                                 else
 238                                         ret = ioprio_best(ret, tmpio);
 239                         } while_each_thread(g, p);
 240
 241                         if (who)
 242                                 free_uid(user);
 243                         break;
 244                 default:
 245                         ret = -EINVAL;
 246         }
 247
 248         read_unlock(&tasklist_lock);
 249         return ret;
 250 }
 251