Root/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
30int 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}
73EXPORT_SYMBOL_GPL(set_task_ioprio);
74
75SYSCALL_DEFINE3(ioprio_set, int, which, int, who, int, ioprio)
76{
77    int class = IOPRIO_PRIO_CLASS(ioprio);
78    int data = IOPRIO_PRIO_DATA(ioprio);
79    struct task_struct *p, *g;
80    struct user_struct *user;
81    struct pid *pgrp;
82    int ret;
83
84    switch (class) {
85        case IOPRIO_CLASS_RT:
86            if (!capable(CAP_SYS_ADMIN))
87                return -EPERM;
88            /* fall through, rt has prio field too */
89        case IOPRIO_CLASS_BE:
90            if (data >= IOPRIO_BE_NR || data < 0)
91                return -EINVAL;
92
93            break;
94        case IOPRIO_CLASS_IDLE:
95            break;
96        case IOPRIO_CLASS_NONE:
97            if (data)
98                return -EINVAL;
99            break;
100        default:
101            return -EINVAL;
102    }
103
104    ret = -ESRCH;
105    /*
106     * We want IOPRIO_WHO_PGRP/IOPRIO_WHO_USER to be "atomic",
107     * so we can't use rcu_read_lock(). See re-copy of ->ioprio
108     * in copy_process().
109     */
110    read_lock(&tasklist_lock);
111    switch (which) {
112        case IOPRIO_WHO_PROCESS:
113            if (!who)
114                p = current;
115            else
116                p = find_task_by_vpid(who);
117            if (p)
118                ret = set_task_ioprio(p, ioprio);
119            break;
120        case IOPRIO_WHO_PGRP:
121            if (!who)
122                pgrp = task_pgrp(current);
123            else
124                pgrp = find_vpid(who);
125            do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
126                ret = set_task_ioprio(p, ioprio);
127                if (ret)
128                    break;
129            } while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
130            break;
131        case IOPRIO_WHO_USER:
132            if (!who)
133                user = current_user();
134            else
135                user = find_user(who);
136
137            if (!user)
138                break;
139
140            do_each_thread(g, p) {
141                if (__task_cred(p)->uid != who)
142                    continue;
143                ret = set_task_ioprio(p, ioprio);
144                if (ret)
145                    goto free_uid;
146            } while_each_thread(g, p);
147free_uid:
148            if (who)
149                free_uid(user);
150            break;
151        default:
152            ret = -EINVAL;
153    }
154
155    read_unlock(&tasklist_lock);
156    return ret;
157}
158
159static int get_task_ioprio(struct task_struct *p)
160{
161    int ret;
162
163    ret = security_task_getioprio(p);
164    if (ret)
165        goto out;
166    ret = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_NONE, IOPRIO_NORM);
167    if (p->io_context)
168        ret = p->io_context->ioprio;
169out:
170    return ret;
171}
172
173int ioprio_best(unsigned short aprio, unsigned short bprio)
174{
175    unsigned short aclass = IOPRIO_PRIO_CLASS(aprio);
176    unsigned short bclass = IOPRIO_PRIO_CLASS(bprio);
177
178    if (aclass == IOPRIO_CLASS_NONE)
179        aclass = IOPRIO_CLASS_BE;
180    if (bclass == IOPRIO_CLASS_NONE)
181        bclass = IOPRIO_CLASS_BE;
182
183    if (aclass == bclass)
184        return min(aprio, bprio);
185    if (aclass > bclass)
186        return bprio;
187    else
188        return aprio;
189}
190
191SYSCALL_DEFINE2(ioprio_get, int, which, int, who)
192{
193    struct task_struct *g, *p;
194    struct user_struct *user;
195    struct pid *pgrp;
196    int ret = -ESRCH;
197    int tmpio;
198
199    read_lock(&tasklist_lock);
200    switch (which) {
201        case IOPRIO_WHO_PROCESS:
202            if (!who)
203                p = current;
204            else
205                p = find_task_by_vpid(who);
206            if (p)
207                ret = get_task_ioprio(p);
208            break;
209        case IOPRIO_WHO_PGRP:
210            if (!who)
211                pgrp = task_pgrp(current);
212            else
213                pgrp = find_vpid(who);
214            do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
215                tmpio = get_task_ioprio(p);
216                if (tmpio < 0)
217                    continue;
218                if (ret == -ESRCH)
219                    ret = tmpio;
220                else
221                    ret = ioprio_best(ret, tmpio);
222            } while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
223            break;
224        case IOPRIO_WHO_USER:
225            if (!who)
226                user = current_user();
227            else
228                user = find_user(who);
229
230            if (!user)
231                break;
232
233            do_each_thread(g, p) {
234                if (__task_cred(p)->uid != user->uid)
235                    continue;
236                tmpio = get_task_ioprio(p);
237                if (tmpio < 0)
238                    continue;
239                if (ret == -ESRCH)
240                    ret = tmpio;
241                else
242                    ret = ioprio_best(ret, tmpio);
243            } while_each_thread(g, p);
244
245            if (who)
246                free_uid(user);
247            break;
248        default:
249            ret = -EINVAL;
250    }
251
252    read_unlock(&tasklist_lock);
253    return ret;
254}
255

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