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/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

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