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                         if (!who)
 115                                 p = current;
 116                         else
 117                                 p = find_task_by_vpid(who);
 118                         if (p)
 119                                 ret = set_task_ioprio(p, ioprio);
 120                         break;
 121                 case IOPRIO_WHO_PGRP:
 122                         if (!who)
 123                                 pgrp = task_pgrp(current);
 124                         else
 125                                 pgrp = find_vpid(who);
 126                         do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
 127                                 ret = set_task_ioprio(p, ioprio);
 128                                 if (ret)
 129                                         break;
 130                         } while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
 131                         break;
 132                 case IOPRIO_WHO_USER:
 133                         if (!who)
 134                                 user = current_user();
 135                         else
 136                                 user = find_user(who);
 137
 138                         if (!user)
 139                                 break;
 140
 141                         do_each_thread(g, p) {
 142                                 if (__task_cred(p)->uid != who)
 143                                         continue;
 144                                 ret = set_task_ioprio(p, ioprio);
 145                                 if (ret)
 146                                         goto free_uid;
 147                         } while_each_thread(g, p);
 148 free_uid:
 149                         if (who)
 150                                 free_uid(user);
 151                         break;
 152                 default:
 153                         ret = -EINVAL;
 154         }
 155
 156         read_unlock(&tasklist_lock);
 157         return ret;
 158 }
 159
 160 static int get_task_ioprio(struct task_struct *p)
 161 {
 162         int ret;
 163
 164         ret = security_task_getioprio(p);
 165         if (ret)
 166                 goto out;
 167         ret = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_NONE, IOPRIO_NORM);
 168         if (p->io_context)
 169                 ret = p->io_context->ioprio;
 170 out:
 171         return ret;
 172 }
 173
 174 int ioprio_best(unsigned short aprio, unsigned short bprio)
 175 {
 176         unsigned short aclass = IOPRIO_PRIO_CLASS(aprio);
 177         unsigned short bclass = IOPRIO_PRIO_CLASS(bprio);
 178
 179         if (aclass == IOPRIO_CLASS_NONE)
 180                 aclass = IOPRIO_CLASS_BE;
 181         if (bclass == IOPRIO_CLASS_NONE)
 182                 bclass = IOPRIO_CLASS_BE;
 183
 184         if (aclass == bclass)
 185                 return min(aprio, bprio);
 186         if (aclass > bclass)
 187                 return bprio;
 188         else
 189                 return aprio;
 190 }
 191
 192 SYSCALL_DEFINE2(ioprio_get, int, which, int, who)
 193 {
 194         struct task_struct *g, *p;
 195         struct user_struct *user;
 196         struct pid *pgrp;
 197         int ret = -ESRCH;
 198         int tmpio;
 199
 200         read_lock(&tasklist_lock);
 201         switch (which) {
 202                 case IOPRIO_WHO_PROCESS:
 203                         if (!who)
 204                                 p = current;
 205                         else
 206                                 p = find_task_by_vpid(who);
 207                         if (p)
 208                                 ret = get_task_ioprio(p);
 209                         break;
 210                 case IOPRIO_WHO_PGRP:
 211                         if (!who)
 212                                 pgrp = task_pgrp(current);
 213                         else
 214                                 pgrp = find_vpid(who);
 215                         do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
 216                                 tmpio = get_task_ioprio(p);
 217                                 if (tmpio < 0)
 218                                         continue;
 219                                 if (ret == -ESRCH)
 220                                         ret = tmpio;
 221                                 else
 222                                         ret = ioprio_best(ret, tmpio);
 223                         } while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
 224                         break;
 225                 case IOPRIO_WHO_USER:
 226                         if (!who)
 227                                 user = current_user();
 228                         else
 229                                 user = find_user(who);
 230
 231                         if (!user)
 232                                 break;
 233
 234                         do_each_thread(g, p) {
 235                                 if (__task_cred(p)->uid != user->uid)
 236                                         continue;
 237                                 tmpio = get_task_ioprio(p);
 238                                 if (tmpio < 0)
 239                                         continue;
 240                                 if (ret == -ESRCH)
 241                                         ret = tmpio;
 242                                 else
 243                                         ret = ioprio_best(ret, tmpio);
 244                         } while_each_thread(g, p);
 245
 246                         if (who)
 247                                 free_uid(user);
 248                         break;
 249                 default:
 250                         ret = -EINVAL;
 251         }
 252
 253         read_unlock(&tasklist_lock);
 254         return ret;
 255 }