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/gfp.h>
  23 #include <linux/kernel.h>
  24 #include <linux/ioprio.h>
  25 #include <linux/blkdev.h>
  26 #include <linux/capability.h>
  27 #include <linux/syscalls.h>
  28 #include <linux/security.h>
  29 #include <linux/pid_namespace.h>
  30
  31 int set_task_ioprio(struct task_struct *task, int ioprio)
  32 {
  33         int err;
  34         struct io_context *ioc;
  35         const struct cred *cred = current_cred(), *tcred;
  36
  37         rcu_read_lock();
  38         tcred = __task_cred(task);
  39         if (tcred->uid != cred->euid &&
  40             tcred->uid != cred->uid && !capable(CAP_SYS_NICE)) {
  41                 rcu_read_unlock();
  42                 return -EPERM;
  43         }
  44         rcu_read_unlock();
  45
  46         err = security_task_setioprio(task, ioprio);
  47         if (err)
  48                 return err;
  49
  50         task_lock(task);
  51         do {
  52                 ioc = task->io_context;
  53                 /* see wmb() in current_io_context() */
  54                 smp_read_barrier_depends();
  55                 if (ioc)
  56                         break;
  57
  58                 ioc = alloc_io_context(GFP_ATOMIC, -1);
  59                 if (!ioc) {
  60                         err = -ENOMEM;
  61                         break;
  62                 }
  63                 task->io_context = ioc;
  64         } while (1);
  65
  66         if (!err) {
  67                 ioc->ioprio = ioprio;
  68                 ioc->ioprio_changed = 1;
  69         }
  70
  71         task_unlock(task);
  72         return err;
  73 }
  74 EXPORT_SYMBOL_GPL(set_task_ioprio);
  75
  76 SYSCALL_DEFINE3(ioprio_set, int, which, int, who, int, ioprio)
  77 {
  78         int class = IOPRIO_PRIO_CLASS(ioprio);
  79         int data = IOPRIO_PRIO_DATA(ioprio);
  80         struct task_struct *p, *g;
  81         struct user_struct *user;
  82         struct pid *pgrp;
  83         int ret;
  84
  85         switch (class) {
  86                 case IOPRIO_CLASS_RT:
  87                         if (!capable(CAP_SYS_ADMIN))
  88                                 return -EPERM;
  89                         /* fall through, rt has prio field too */
  90                 case IOPRIO_CLASS_BE:
  91                         if (data >= IOPRIO_BE_NR || data < 0)
  92                                 return -EINVAL;
  93
  94                         break;
  95                 case IOPRIO_CLASS_IDLE:
  96                         break;
  97                 case IOPRIO_CLASS_NONE:
  98                         if (data)
  99                                 return -EINVAL;
 100                         break;
 101                 default:
 102                         return -EINVAL;
 103         }
 104
 105         ret = -ESRCH;
 106         /*
 107          * We want IOPRIO_WHO_PGRP/IOPRIO_WHO_USER to be "atomic",
 108          * so we can't use rcu_read_lock(). See re-copy of ->ioprio
 109          * in copy_process().
 110          */
 111         read_lock(&tasklist_lock);
 112         switch (which) {
 113                 case IOPRIO_WHO_PROCESS:
 114                         rcu_read_lock();
 115                         if (!who)
 116                                 p = current;
 117                         else
 118                                 p = find_task_by_vpid(who);
 119                         if (p)
 120                                 ret = set_task_ioprio(p, ioprio);
 121                         rcu_read_unlock();
 122                         break;
 123                 case IOPRIO_WHO_PGRP:
 124                         if (!who)
 125                                 pgrp = task_pgrp(current);
 126                         else
 127                                 pgrp = find_vpid(who);
 128                         do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
 129                                 ret = set_task_ioprio(p, ioprio);
 130                                 if (ret)
 131                                         break;
 132                         } while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
 133                         break;
 134                 case IOPRIO_WHO_USER:
 135                         if (!who)
 136                                 user = current_user();
 137                         else
 138                                 user = find_user(who);
 139
 140                         if (!user)
 141                                 break;
 142
 143                         do_each_thread(g, p) {
 144                                 int match;
 145
 146                                 rcu_read_lock();
 147                                 match = __task_cred(p)->uid == who;
 148                                 rcu_read_unlock();
 149                                 if (!match)
 150                                         continue;
 151                                 ret = set_task_ioprio(p, ioprio);
 152                                 if (ret)
 153                                         goto free_uid;
 154                         } while_each_thread(g, p);
 155 free_uid:
 156                         if (who)
 157                                 free_uid(user);
 158                         break;
 159                 default:
 160                         ret = -EINVAL;
 161         }
 162
 163         read_unlock(&tasklist_lock);
 164         return ret;
 165 }
 166
 167 static int get_task_ioprio(struct task_struct *p)
 168 {
 169         int ret;
 170
 171         ret = security_task_getioprio(p);
 172         if (ret)
 173                 goto out;
 174         ret = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_NONE, IOPRIO_NORM);
 175         if (p->io_context)
 176                 ret = p->io_context->ioprio;
 177 out:
 178         return ret;
 179 }
 180
 181 int ioprio_best(unsigned short aprio, unsigned short bprio)
 182 {
 183         unsigned short aclass = IOPRIO_PRIO_CLASS(aprio);
 184         unsigned short bclass = IOPRIO_PRIO_CLASS(bprio);
 185
 186         if (aclass == IOPRIO_CLASS_NONE)
 187                 aclass = IOPRIO_CLASS_BE;
 188         if (bclass == IOPRIO_CLASS_NONE)
 189                 bclass = IOPRIO_CLASS_BE;
 190
 191         if (aclass == bclass)
 192                 return min(aprio, bprio);
 193         if (aclass > bclass)
 194                 return bprio;
 195         else
 196                 return aprio;
 197 }
 198
 199 SYSCALL_DEFINE2(ioprio_get, int, which, int, who)
 200 {
 201         struct task_struct *g, *p;
 202         struct user_struct *user;
 203         struct pid *pgrp;
 204         int ret = -ESRCH;
 205         int tmpio;
 206
 207         read_lock(&tasklist_lock);
 208         switch (which) {
 209                 case IOPRIO_WHO_PROCESS:
 210                         rcu_read_lock();
 211                         if (!who)
 212                                 p = current;
 213                         else
 214                                 p = find_task_by_vpid(who);
 215                         if (p)
 216                                 ret = get_task_ioprio(p);
 217                         rcu_read_unlock();
 218                         break;
 219                 case IOPRIO_WHO_PGRP:
 220                         if (!who)
 221                                 pgrp = task_pgrp(current);
 222                         else
 223                                 pgrp = find_vpid(who);
 224                         do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
 225                                 tmpio = get_task_ioprio(p);
 226                                 if (tmpio < 0)
 227                                         continue;
 228                                 if (ret == -ESRCH)
 229                                         ret = tmpio;
 230                                 else
 231                                         ret = ioprio_best(ret, tmpio);
 232                         } while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
 233                         break;
 234                 case IOPRIO_WHO_USER:
 235                         if (!who)
 236                                 user = current_user();
 237                         else
 238                                 user = find_user(who);
 239
 240                         if (!user)
 241                                 break;
 242
 243                         do_each_thread(g, p) {
 244                                 int match;
 245
 246                                 rcu_read_lock();
 247                                 match = __task_cred(p)->uid == user->uid;
 248                                 rcu_read_unlock();
 249                                 if (!match)
 250                                         continue;
 251                                 tmpio = get_task_ioprio(p);
 252                                 if (tmpio < 0)
 253                                         continue;
 254                                 if (ret == -ESRCH)
 255                                         ret = tmpio;
 256                                 else
 257                                         ret = ioprio_best(ret, tmpio);
 258                         } while_each_thread(g, p);
 259
 260                         if (who)
 261                                 free_uid(user);
 262                         break;
 263                 default:
 264                         ret = -EINVAL;
 265         }
 266
 267         read_unlock(&tasklist_lock);
 268         return ret;
 269 }