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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 int set_task_ioprio(struct task_struct *task, int ioprio)
  31 {
  32         int err;
  33         struct io_context *ioc;
  34         const struct cred *cred = current_cred(), *tcred;
  35
  36         rcu_read_lock();
  37         tcred = __task_cred(task);
  38         if (tcred->uid != cred->euid &&
  39             tcred->uid != cred->uid && !capable(CAP_SYS_NICE)) {
  40                 rcu_read_unlock();
  41                 return -EPERM;
  42         }
  43         rcu_read_unlock();
  44
  45         err = security_task_setioprio(task, ioprio);
  46         if (err)
  47                 return err;
  48
  49         task_lock(task);
  50         do {
  51                 ioc = task->io_context;
  52                 /* see wmb() in current_io_context() */
  53                 smp_read_barrier_depends();
  54                 if (ioc)
  55                         break;
  56
  57                 ioc = alloc_io_context(GFP_ATOMIC, -1);
  58                 if (!ioc) {
  59                         err = -ENOMEM;
  60                         break;
  61                 }
  62                 task->io_context = ioc;
  63         } while (1);
  64
  65         if (!err) {
  66                 ioc->ioprio = ioprio;
  67                 ioc->ioprio_changed = 1;
  68         }
  69
  70         task_unlock(task);
  71         return err;
  72 }
  73 EXPORT_SYMBOL_GPL(set_task_ioprio);
  74
  75 SYSCALL_DEFINE3(ioprio_set, int, which, int, who, int, ioprio)
  76 {
  77         int class = IOPRIO_PRIO_CLASS(ioprio);
  78         int data = IOPRIO_PRIO_DATA(ioprio);
  79         struct task_struct *p, *g;
  80         struct user_struct *user;
  81         struct pid *pgrp;
  82         int ret;
  83
  84         switch (class) {
  85                 case IOPRIO_CLASS_RT:
  86                         if (!capable(CAP_SYS_ADMIN))
  87                                 return -EPERM;
  88                         /* fall through, rt has prio field too */
  89                 case IOPRIO_CLASS_BE:
  90                         if (data >= IOPRIO_BE_NR || data < 0)
  91                                 return -EINVAL;
  92
  93                         break;
  94                 case IOPRIO_CLASS_IDLE:
  95                         break;
  96                 case IOPRIO_CLASS_NONE:
  97                         if (data)
  98                                 return -EINVAL;
  99                         break;
 100                 default:
 101                         return -EINVAL;
 102         }
 103
 104         ret = -ESRCH;
 105         /*
 106          * We want IOPRIO_WHO_PGRP/IOPRIO_WHO_USER to be "atomic",
 107          * so we can't use rcu_read_lock(). See re-copy of ->ioprio
 108          * in copy_process().
 109          */
 110         read_lock(&tasklist_lock);
 111         switch (which) {
 112                 case IOPRIO_WHO_PROCESS:
 113                         if (!who)
 114                                 p = current;
 115                         else
 116                                 p = find_task_by_vpid(who);
 117                         if (p)
 118                                 ret = set_task_ioprio(p, ioprio);
 119                         break;
 120                 case IOPRIO_WHO_PGRP:
 121                         if (!who)
 122                                 pgrp = task_pgrp(current);
 123                         else
 124                                 pgrp = find_vpid(who);
 125                         do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
 126                                 ret = set_task_ioprio(p, ioprio);
 127                                 if (ret)
 128                                         break;
 129                         } while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
 130                         break;
 131                 case IOPRIO_WHO_USER:
 132                         if (!who)
 133                                 user = current_user();
 134                         else
 135                                 user = find_user(who);
 136
 137                         if (!user)
 138                                 break;
 139
 140                         do_each_thread(g, p) {
 141                                 if (__task_cred(p)->uid != who)
 142                                         continue;
 143                                 ret = set_task_ioprio(p, ioprio);
 144                                 if (ret)
 145                                         goto free_uid;
 146                         } while_each_thread(g, p);
 147 free_uid:
 148                         if (who)
 149                                 free_uid(user);
 150                         break;
 151                 default:
 152                         ret = -EINVAL;
 153         }
 154
 155         read_unlock(&tasklist_lock);
 156         return ret;
 157 }
 158
 159 static int get_task_ioprio(struct task_struct *p)
 160 {
 161         int ret;
 162
 163         ret = security_task_getioprio(p);
 164         if (ret)
 165                 goto out;
 166         ret = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_NONE, IOPRIO_NORM);
 167         if (p->io_context)
 168                 ret = p->io_context->ioprio;
 169 out:
 170         return ret;
 171 }
 172
 173 int ioprio_best(unsigned short aprio, unsigned short bprio)
 174 {
 175         unsigned short aclass = IOPRIO_PRIO_CLASS(aprio);
 176         unsigned short bclass = IOPRIO_PRIO_CLASS(bprio);
 177
 178         if (aclass == IOPRIO_CLASS_NONE)
 179                 aclass = IOPRIO_CLASS_BE;
 180         if (bclass == IOPRIO_CLASS_NONE)
 181                 bclass = IOPRIO_CLASS_BE;
 182
 183         if (aclass == bclass)
 184                 return min(aprio, bprio);
 185         if (aclass > bclass)
 186                 return bprio;
 187         else
 188                 return aprio;
 189 }
 190
 191 SYSCALL_DEFINE2(ioprio_get, int, which, int, who)
 192 {
 193         struct task_struct *g, *p;
 194         struct user_struct *user;
 195         struct pid *pgrp;
 196         int ret = -ESRCH;
 197         int tmpio;
 198
 199         read_lock(&tasklist_lock);
 200         switch (which) {
 201                 case IOPRIO_WHO_PROCESS:
 202                         if (!who)
 203                                 p = current;
 204                         else
 205                                 p = find_task_by_vpid(who);
 206                         if (p)
 207                                 ret = get_task_ioprio(p);
 208                         break;
 209                 case IOPRIO_WHO_PGRP:
 210                         if (!who)
 211                                 pgrp = task_pgrp(current);
 212                         else
 213                                 pgrp = find_vpid(who);
 214                         do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
 215                                 tmpio = get_task_ioprio(p);
 216                                 if (tmpio < 0)
 217                                         continue;
 218                                 if (ret == -ESRCH)
 219                                         ret = tmpio;
 220                                 else
 221                                         ret = ioprio_best(ret, tmpio);
 222                         } while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
 223                         break;
 224                 case IOPRIO_WHO_USER:
 225                         if (!who)
 226                                 user = current_user();
 227                         else
 228                                 user = find_user(who);
 229
 230                         if (!user)
 231                                 break;
 232
 233                         do_each_thread(g, p) {
 234                                 if (__task_cred(p)->uid != user->uid)
 235                                         continue;
 236                                 tmpio = get_task_ioprio(p);
 237                                 if (tmpio < 0)
 238                                         continue;
 239                                 if (ret == -ESRCH)
 240                                         ret = tmpio;
 241                                 else
 242                                         ret = ioprio_best(ret, tmpio);
 243                         } while_each_thread(g, p);
 244
 245                         if (who)
 246                                 free_uid(user);
 247                         break;
 248                 default:
 249                         ret = -EINVAL;
 250         }
 251
 252         read_unlock(&tasklist_lock);
 253         return ret;
 254 }