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