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/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         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
  74 asmlinkage long sys_ioprio_set(int which, int who, int ioprio)
  75 {
  76         int class = IOPRIO_PRIO_CLASS(ioprio);
  77         int data = IOPRIO_PRIO_DATA(ioprio);
  78         struct task_struct *p, *g;
  79         struct user_struct *user;
  80         struct pid *pgrp;
  81         int ret;
  82
  83         switch (class) {
  84                 case IOPRIO_CLASS_RT:
  85                         if (!capable(CAP_SYS_ADMIN))
  86                                 return -EPERM;
  87                         /* fall through, rt has prio field too */
  88                 case IOPRIO_CLASS_BE:
  89                         if (data >= IOPRIO_BE_NR || data < 0)
  90                                 return -EINVAL;
  91
  92                         break;
  93                 case IOPRIO_CLASS_IDLE:
  94                         break;
  95                 case IOPRIO_CLASS_NONE:
  96                         if (data)
  97                                 return -EINVAL;
  98                         break;
  99                 default:
 100                         return -EINVAL;
 101         }
 102
 103         ret = -ESRCH;
 104         /*
 105          * We want IOPRIO_WHO_PGRP/IOPRIO_WHO_USER to be "atomic",
 106          * so we can't use rcu_read_lock(). See re-copy of ->ioprio
 107          * in copy_process().
 108          */
 109         read_lock(&tasklist_lock);
 110         switch (which) {
 111                 case IOPRIO_WHO_PROCESS:
 112                         if (!who)
 113                                 p = current;
 114                         else
 115                                 p = find_task_by_vpid(who);
 116                         if (p)
 117                                 ret = set_task_ioprio(p, ioprio);
 118                         break;
 119                 case IOPRIO_WHO_PGRP:
 120                         if (!who)
 121                                 pgrp = task_pgrp(current);
 122                         else
 123                                 pgrp = find_vpid(who);
 124                         do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
 125                                 ret = set_task_ioprio(p, ioprio);
 126                                 if (ret)
 127                                         break;
 128                         } while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
 129                         break;
 130                 case IOPRIO_WHO_USER:
 131                         if (!who)
 132                                 user = current_user();
 133                         else
 134                                 user = find_user(who);
 135
 136                         if (!user)
 137                                 break;
 138
 139                         do_each_thread(g, p) {
 140                                 if (__task_cred(p)->uid != who)
 141                                         continue;
 142                                 ret = set_task_ioprio(p, ioprio);
 143                                 if (ret)
 144                                         goto free_uid;
 145                         } while_each_thread(g, p);
 146 free_uid:
 147                         if (who)
 148                                 free_uid(user);
 149                         break;
 150                 default:
 151                         ret = -EINVAL;
 152         }
 153
 154         read_unlock(&tasklist_lock);
 155         return ret;
 156 }
 157
 158 static int get_task_ioprio(struct task_struct *p)
 159 {
 160         int ret;
 161
 162         ret = security_task_getioprio(p);
 163         if (ret)
 164                 goto out;
 165         ret = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_NONE, IOPRIO_NORM);
 166         if (p->io_context)
 167                 ret = p->io_context->ioprio;
 168 out:
 169         return ret;
 170 }
 171
 172 int ioprio_best(unsigned short aprio, unsigned short bprio)
 173 {
 174         unsigned short aclass = IOPRIO_PRIO_CLASS(aprio);
 175         unsigned short bclass = IOPRIO_PRIO_CLASS(bprio);
 176
 177         if (aclass == IOPRIO_CLASS_NONE)
 178                 aclass = IOPRIO_CLASS_BE;
 179         if (bclass == IOPRIO_CLASS_NONE)
 180                 bclass = IOPRIO_CLASS_BE;
 181
 182         if (aclass == bclass)
 183                 return min(aprio, bprio);
 184         if (aclass > bclass)
 185                 return bprio;
 186         else
 187                 return aprio;
 188 }
 189
 190 asmlinkage long sys_ioprio_get(int which, int who)
 191 {
 192         struct task_struct *g, *p;
 193         struct user_struct *user;
 194         struct pid *pgrp;
 195         int ret = -ESRCH;
 196         int tmpio;
 197
 198         read_lock(&tasklist_lock);
 199         switch (which) {
 200                 case IOPRIO_WHO_PROCESS:
 201                         if (!who)
 202                                 p = current;
 203                         else
 204                                 p = find_task_by_vpid(who);
 205                         if (p)
 206                                 ret = get_task_ioprio(p);
 207                         break;
 208                 case IOPRIO_WHO_PGRP:
 209                         if (!who)
 210                                 pgrp = task_pgrp(current);
 211                         else
 212                                 pgrp = find_vpid(who);
 213                         do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
 214                                 tmpio = get_task_ioprio(p);
 215                                 if (tmpio < 0)
 216                                         continue;
 217                                 if (ret == -ESRCH)
 218                                         ret = tmpio;
 219                                 else
 220                                         ret = ioprio_best(ret, tmpio);
 221                         } while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
 222                         break;
 223                 case IOPRIO_WHO_USER:
 224                         if (!who)
 225                                 user = current_user();
 226                         else
 227                                 user = find_user(who);
 228
 229                         if (!user)
 230                                 break;
 231
 232                         do_each_thread(g, p) {
 233                                 if (__task_cred(p)->uid != user->uid)
 234                                         continue;
 235                                 tmpio = get_task_ioprio(p);
 236                                 if (tmpio < 0)
 237                                         continue;
 238                                 if (ret == -ESRCH)
 239                                         ret = tmpio;
 240                                 else
 241                                         ret = ioprio_best(ret, tmpio);
 242                         } while_each_thread(g, p);
 243
 244                         if (who)
 245                                 free_uid(user);
 246                         break;
 247                 default:
 248                         ret = -EINVAL;
 249         }
 250
 251         read_unlock(&tasklist_lock);
 252         return ret;
 253 }
 254