linux/fs/ioprio.c
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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/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
  31int 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}
  74EXPORT_SYMBOL_GPL(set_task_ioprio);
  75
  76SYSCALL_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        rcu_read_lock();
 107        switch (which) {
 108                case IOPRIO_WHO_PROCESS:
 109                        if (!who)
 110                                p = current;
 111                        else
 112                                p = find_task_by_vpid(who);
 113                        if (p)
 114                                ret = set_task_ioprio(p, ioprio);
 115                        break;
 116                case IOPRIO_WHO_PGRP:
 117                        if (!who)
 118                                pgrp = task_pgrp(current);
 119                        else
 120                                pgrp = find_vpid(who);
 121                        do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
 122                                ret = set_task_ioprio(p, ioprio);
 123                                if (ret)
 124                                        break;
 125                        } while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
 126                        break;
 127                case IOPRIO_WHO_USER:
 128                        if (!who)
 129                                user = current_user();
 130                        else
 131                                user = find_user(who);
 132
 133                        if (!user)
 134                                break;
 135
 136                        do_each_thread(g, p) {
 137                                if (__task_cred(p)->uid != who)
 138                                        continue;
 139                                ret = set_task_ioprio(p, ioprio);
 140                                if (ret)
 141                                        goto free_uid;
 142                        } while_each_thread(g, p);
 143free_uid:
 144                        if (who)
 145                                free_uid(user);
 146                        break;
 147                default:
 148                        ret = -EINVAL;
 149        }
 150
 151        rcu_read_unlock();
 152        return ret;
 153}
 154
 155static int get_task_ioprio(struct task_struct *p)
 156{
 157        int ret;
 158
 159        ret = security_task_getioprio(p);
 160        if (ret)
 161                goto out;
 162        ret = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_NONE, IOPRIO_NORM);
 163        if (p->io_context)
 164                ret = p->io_context->ioprio;
 165out:
 166        return ret;
 167}
 168
 169int ioprio_best(unsigned short aprio, unsigned short bprio)
 170{
 171        unsigned short aclass = IOPRIO_PRIO_CLASS(aprio);
 172        unsigned short bclass = IOPRIO_PRIO_CLASS(bprio);
 173
 174        if (aclass == IOPRIO_CLASS_NONE)
 175                aclass = IOPRIO_CLASS_BE;
 176        if (bclass == IOPRIO_CLASS_NONE)
 177                bclass = IOPRIO_CLASS_BE;
 178
 179        if (aclass == bclass)
 180                return min(aprio, bprio);
 181        if (aclass > bclass)
 182                return bprio;
 183        else
 184                return aprio;
 185}
 186
 187SYSCALL_DEFINE2(ioprio_get, int, which, int, who)
 188{
 189        struct task_struct *g, *p;
 190        struct user_struct *user;
 191        struct pid *pgrp;
 192        int ret = -ESRCH;
 193        int tmpio;
 194
 195        rcu_read_lock();
 196        switch (which) {
 197                case IOPRIO_WHO_PROCESS:
 198                        if (!who)
 199                                p = current;
 200                        else
 201                                p = find_task_by_vpid(who);
 202                        if (p)
 203                                ret = get_task_ioprio(p);
 204                        break;
 205                case IOPRIO_WHO_PGRP:
 206                        if (!who)
 207                                pgrp = task_pgrp(current);
 208                        else
 209                                pgrp = find_vpid(who);
 210                        do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
 211                                tmpio = get_task_ioprio(p);
 212                                if (tmpio < 0)
 213                                        continue;
 214                                if (ret == -ESRCH)
 215                                        ret = tmpio;
 216                                else
 217                                        ret = ioprio_best(ret, tmpio);
 218                        } while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
 219                        break;
 220                case IOPRIO_WHO_USER:
 221                        if (!who)
 222                                user = current_user();
 223                        else
 224                                user = find_user(who);
 225
 226                        if (!user)
 227                                break;
 228
 229                        do_each_thread(g, p) {
 230                                if (__task_cred(p)->uid != user->uid)
 231                                        continue;
 232                                tmpio = get_task_ioprio(p);
 233                                if (tmpio < 0)
 234                                        continue;
 235                                if (ret == -ESRCH)
 236                                        ret = tmpio;
 237                                else
 238                                        ret = ioprio_best(ret, tmpio);
 239                        } while_each_thread(g, p);
 240
 241                        if (who)
 242                                free_uid(user);
 243                        break;
 244                default:
 245                        ret = -EINVAL;
 246        }
 247
 248        rcu_read_unlock();
 249        return ret;
 250}
 251
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