linux/block/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/export.h>
  25#include <linux/ioprio.h>
  26#include <linux/blkdev.h>
  27#include <linux/capability.h>
  28#include <linux/syscalls.h>
  29#include <linux/security.h>
  30#include <linux/pid_namespace.h>
  31
  32int set_task_ioprio(struct task_struct *task, int ioprio)
  33{
  34        int err;
  35        struct io_context *ioc;
  36        const struct cred *cred = current_cred(), *tcred;
  37
  38        rcu_read_lock();
  39        tcred = __task_cred(task);
  40        if (!uid_eq(tcred->uid, cred->euid) &&
  41            !uid_eq(tcred->uid, cred->uid) && !capable(CAP_SYS_NICE)) {
  42                rcu_read_unlock();
  43                return -EPERM;
  44        }
  45        rcu_read_unlock();
  46
  47        err = security_task_setioprio(task, ioprio);
  48        if (err)
  49                return err;
  50
  51        ioc = get_task_io_context(task, GFP_ATOMIC, NUMA_NO_NODE);
  52        if (ioc) {
  53                ioc->ioprio = ioprio;
  54                put_io_context(ioc);
  55        }
  56
  57        return err;
  58}
  59EXPORT_SYMBOL_GPL(set_task_ioprio);
  60
  61SYSCALL_DEFINE3(ioprio_set, int, which, int, who, int, ioprio)
  62{
  63        int class = IOPRIO_PRIO_CLASS(ioprio);
  64        int data = IOPRIO_PRIO_DATA(ioprio);
  65        struct task_struct *p, *g;
  66        struct user_struct *user;
  67        struct pid *pgrp;
  68        kuid_t uid;
  69        int ret;
  70
  71        switch (class) {
  72                case IOPRIO_CLASS_RT:
  73                        if (!capable(CAP_SYS_ADMIN))
  74                                return -EPERM;
  75                        /* fall through, rt has prio field too */
  76                case IOPRIO_CLASS_BE:
  77                        if (data >= IOPRIO_BE_NR || data < 0)
  78                                return -EINVAL;
  79
  80                        break;
  81                case IOPRIO_CLASS_IDLE:
  82                        break;
  83                case IOPRIO_CLASS_NONE:
  84                        if (data)
  85                                return -EINVAL;
  86                        break;
  87                default:
  88                        return -EINVAL;
  89        }
  90
  91        ret = -ESRCH;
  92        rcu_read_lock();
  93        switch (which) {
  94                case IOPRIO_WHO_PROCESS:
  95                        if (!who)
  96                                p = current;
  97                        else
  98                                p = find_task_by_vpid(who);
  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_thread(pgrp, PIDTYPE_PGID, p) {
 108                                ret = set_task_ioprio(p, ioprio);
 109                                if (ret)
 110                                        break;
 111                        } while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
 112                        break;
 113                case IOPRIO_WHO_USER:
 114                        uid = make_kuid(current_user_ns(), who);
 115                        if (!uid_valid(uid))
 116                                break;
 117                        if (!who)
 118                                user = current_user();
 119                        else
 120                                user = find_user(uid);
 121
 122                        if (!user)
 123                                break;
 124
 125                        do_each_thread(g, p) {
 126                                if (!uid_eq(task_uid(p), uid) ||
 127                                    !task_pid_vnr(p))
 128                                        continue;
 129                                ret = set_task_ioprio(p, ioprio);
 130                                if (ret)
 131                                        goto free_uid;
 132                        } while_each_thread(g, p);
 133free_uid:
 134                        if (who)
 135                                free_uid(user);
 136                        break;
 137                default:
 138                        ret = -EINVAL;
 139        }
 140
 141        rcu_read_unlock();
 142        return ret;
 143}
 144
 145static int get_task_ioprio(struct task_struct *p)
 146{
 147        int ret;
 148
 149        ret = security_task_getioprio(p);
 150        if (ret)
 151                goto out;
 152        ret = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_NONE, IOPRIO_NORM);
 153        task_lock(p);
 154        if (p->io_context)
 155                ret = p->io_context->ioprio;
 156        task_unlock(p);
 157out:
 158        return ret;
 159}
 160
 161int ioprio_best(unsigned short aprio, unsigned short bprio)
 162{
 163        unsigned short aclass;
 164        unsigned short bclass;
 165
 166        if (!ioprio_valid(aprio))
 167                aprio = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_BE, IOPRIO_NORM);
 168        if (!ioprio_valid(bprio))
 169                bprio = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_BE, IOPRIO_NORM);
 170
 171        aclass = IOPRIO_PRIO_CLASS(aprio);
 172        bclass = IOPRIO_PRIO_CLASS(bprio);
 173        if (aclass == bclass)
 174                return min(aprio, bprio);
 175        if (aclass > bclass)
 176                return bprio;
 177        else
 178                return aprio;
 179}
 180
 181SYSCALL_DEFINE2(ioprio_get, int, which, int, who)
 182{
 183        struct task_struct *g, *p;
 184        struct user_struct *user;
 185        struct pid *pgrp;
 186        kuid_t uid;
 187        int ret = -ESRCH;
 188        int tmpio;
 189
 190        rcu_read_lock();
 191        switch (which) {
 192                case IOPRIO_WHO_PROCESS:
 193                        if (!who)
 194                                p = current;
 195                        else
 196                                p = find_task_by_vpid(who);
 197                        if (p)
 198                                ret = get_task_ioprio(p);
 199                        break;
 200                case IOPRIO_WHO_PGRP:
 201                        if (!who)
 202                                pgrp = task_pgrp(current);
 203                        else
 204                                pgrp = find_vpid(who);
 205                        do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
 206                                tmpio = get_task_ioprio(p);
 207                                if (tmpio < 0)
 208                                        continue;
 209                                if (ret == -ESRCH)
 210                                        ret = tmpio;
 211                                else
 212                                        ret = ioprio_best(ret, tmpio);
 213                        } while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
 214                        break;
 215                case IOPRIO_WHO_USER:
 216                        uid = make_kuid(current_user_ns(), who);
 217                        if (!who)
 218                                user = current_user();
 219                        else
 220                                user = find_user(uid);
 221
 222                        if (!user)
 223                                break;
 224
 225                        do_each_thread(g, p) {
 226                                if (!uid_eq(task_uid(p), user->uid) ||
 227                                    !task_pid_vnr(p))
 228                                        continue;
 229                                tmpio = get_task_ioprio(p);
 230                                if (tmpio < 0)
 231                                        continue;
 232                                if (ret == -ESRCH)
 233                                        ret = tmpio;
 234                                else
 235                                        ret = ioprio_best(ret, tmpio);
 236                        } while_each_thread(g, p);
 237
 238                        if (who)
 239                                free_uid(user);
 240                        break;
 241                default:
 242                        ret = -EINVAL;
 243        }
 244
 245        rcu_read_unlock();
 246        return ret;
 247}
 248