LXR linux/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
  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        /*
 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);
 148free_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
 160static 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;
 170out:
 171        return ret;
 172}
 173
 174int 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
 192SYSCALL_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}
 256