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