Root/fs/timerfd.c

1/*
2 * fs/timerfd.c
3 *
4 * Copyright (C) 2007 Davide Libenzi <davidel@xmailserver.org>
5 *
6 *
7 * Thanks to Thomas Gleixner for code reviews and useful comments.
8 *
9 */
10
11#include <linux/file.h>
12#include <linux/poll.h>
13#include <linux/init.h>
14#include <linux/fs.h>
15#include <linux/sched.h>
16#include <linux/kernel.h>
17#include <linux/list.h>
18#include <linux/spinlock.h>
19#include <linux/time.h>
20#include <linux/hrtimer.h>
21#include <linux/anon_inodes.h>
22#include <linux/timerfd.h>
23#include <linux/syscalls.h>
24
25struct timerfd_ctx {
26    struct hrtimer tmr;
27    ktime_t tintv;
28    wait_queue_head_t wqh;
29    u64 ticks;
30    int expired;
31    int clockid;
32};
33
34/*
35 * This gets called when the timer event triggers. We set the "expired"
36 * flag, but we do not re-arm the timer (in case it's necessary,
37 * tintv.tv64 != 0) until the timer is accessed.
38 */
39static enum hrtimer_restart timerfd_tmrproc(struct hrtimer *htmr)
40{
41    struct timerfd_ctx *ctx = container_of(htmr, struct timerfd_ctx, tmr);
42    unsigned long flags;
43
44    spin_lock_irqsave(&ctx->wqh.lock, flags);
45    ctx->expired = 1;
46    ctx->ticks++;
47    wake_up_locked(&ctx->wqh);
48    spin_unlock_irqrestore(&ctx->wqh.lock, flags);
49
50    return HRTIMER_NORESTART;
51}
52
53static ktime_t timerfd_get_remaining(struct timerfd_ctx *ctx)
54{
55    ktime_t remaining;
56
57    remaining = hrtimer_expires_remaining(&ctx->tmr);
58    return remaining.tv64 < 0 ? ktime_set(0, 0): remaining;
59}
60
61static void timerfd_setup(struct timerfd_ctx *ctx, int flags,
62              const struct itimerspec *ktmr)
63{
64    enum hrtimer_mode htmode;
65    ktime_t texp;
66
67    htmode = (flags & TFD_TIMER_ABSTIME) ?
68        HRTIMER_MODE_ABS: HRTIMER_MODE_REL;
69
70    texp = timespec_to_ktime(ktmr->it_value);
71    ctx->expired = 0;
72    ctx->ticks = 0;
73    ctx->tintv = timespec_to_ktime(ktmr->it_interval);
74    hrtimer_init(&ctx->tmr, ctx->clockid, htmode);
75    hrtimer_set_expires(&ctx->tmr, texp);
76    ctx->tmr.function = timerfd_tmrproc;
77    if (texp.tv64 != 0)
78        hrtimer_start(&ctx->tmr, texp, htmode);
79}
80
81static int timerfd_release(struct inode *inode, struct file *file)
82{
83    struct timerfd_ctx *ctx = file->private_data;
84
85    hrtimer_cancel(&ctx->tmr);
86    kfree(ctx);
87    return 0;
88}
89
90static unsigned int timerfd_poll(struct file *file, poll_table *wait)
91{
92    struct timerfd_ctx *ctx = file->private_data;
93    unsigned int events = 0;
94    unsigned long flags;
95
96    poll_wait(file, &ctx->wqh, wait);
97
98    spin_lock_irqsave(&ctx->wqh.lock, flags);
99    if (ctx->ticks)
100        events |= POLLIN;
101    spin_unlock_irqrestore(&ctx->wqh.lock, flags);
102
103    return events;
104}
105
106static ssize_t timerfd_read(struct file *file, char __user *buf, size_t count,
107                loff_t *ppos)
108{
109    struct timerfd_ctx *ctx = file->private_data;
110    ssize_t res;
111    u64 ticks = 0;
112    DECLARE_WAITQUEUE(wait, current);
113
114    if (count < sizeof(ticks))
115        return -EINVAL;
116    spin_lock_irq(&ctx->wqh.lock);
117    res = -EAGAIN;
118    if (!ctx->ticks && !(file->f_flags & O_NONBLOCK)) {
119        __add_wait_queue(&ctx->wqh, &wait);
120        for (res = 0;;) {
121            set_current_state(TASK_INTERRUPTIBLE);
122            if (ctx->ticks) {
123                res = 0;
124                break;
125            }
126            if (signal_pending(current)) {
127                res = -ERESTARTSYS;
128                break;
129            }
130            spin_unlock_irq(&ctx->wqh.lock);
131            schedule();
132            spin_lock_irq(&ctx->wqh.lock);
133        }
134        __remove_wait_queue(&ctx->wqh, &wait);
135        __set_current_state(TASK_RUNNING);
136    }
137    if (ctx->ticks) {
138        ticks = ctx->ticks;
139        if (ctx->expired && ctx->tintv.tv64) {
140            /*
141             * If tintv.tv64 != 0, this is a periodic timer that
142             * needs to be re-armed. We avoid doing it in the timer
143             * callback to avoid DoS attacks specifying a very
144             * short timer period.
145             */
146            ticks += hrtimer_forward_now(&ctx->tmr,
147                             ctx->tintv) - 1;
148            hrtimer_restart(&ctx->tmr);
149        }
150        ctx->expired = 0;
151        ctx->ticks = 0;
152    }
153    spin_unlock_irq(&ctx->wqh.lock);
154    if (ticks)
155        res = put_user(ticks, (u64 __user *) buf) ? -EFAULT: sizeof(ticks);
156    return res;
157}
158
159static const struct file_operations timerfd_fops = {
160    .release = timerfd_release,
161    .poll = timerfd_poll,
162    .read = timerfd_read,
163};
164
165static struct file *timerfd_fget(int fd)
166{
167    struct file *file;
168
169    file = fget(fd);
170    if (!file)
171        return ERR_PTR(-EBADF);
172    if (file->f_op != &timerfd_fops) {
173        fput(file);
174        return ERR_PTR(-EINVAL);
175    }
176
177    return file;
178}
179
180SYSCALL_DEFINE2(timerfd_create, int, clockid, int, flags)
181{
182    int ufd;
183    struct timerfd_ctx *ctx;
184
185    /* Check the TFD_* constants for consistency. */
186    BUILD_BUG_ON(TFD_CLOEXEC != O_CLOEXEC);
187    BUILD_BUG_ON(TFD_NONBLOCK != O_NONBLOCK);
188
189    if ((flags & ~TFD_CREATE_FLAGS) ||
190        (clockid != CLOCK_MONOTONIC &&
191         clockid != CLOCK_REALTIME))
192        return -EINVAL;
193
194    ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
195    if (!ctx)
196        return -ENOMEM;
197
198    init_waitqueue_head(&ctx->wqh);
199    ctx->clockid = clockid;
200    hrtimer_init(&ctx->tmr, clockid, HRTIMER_MODE_ABS);
201
202    ufd = anon_inode_getfd("[timerfd]", &timerfd_fops, ctx,
203                   flags & TFD_SHARED_FCNTL_FLAGS);
204    if (ufd < 0)
205        kfree(ctx);
206
207    return ufd;
208}
209
210SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
211        const struct itimerspec __user *, utmr,
212        struct itimerspec __user *, otmr)
213{
214    struct file *file;
215    struct timerfd_ctx *ctx;
216    struct itimerspec ktmr, kotmr;
217
218    if (copy_from_user(&ktmr, utmr, sizeof(ktmr)))
219        return -EFAULT;
220
221    if ((flags & ~TFD_SETTIME_FLAGS) ||
222        !timespec_valid(&ktmr.it_value) ||
223        !timespec_valid(&ktmr.it_interval))
224        return -EINVAL;
225
226    file = timerfd_fget(ufd);
227    if (IS_ERR(file))
228        return PTR_ERR(file);
229    ctx = file->private_data;
230
231    /*
232     * We need to stop the existing timer before reprogramming
233     * it to the new values.
234     */
235    for (;;) {
236        spin_lock_irq(&ctx->wqh.lock);
237        if (hrtimer_try_to_cancel(&ctx->tmr) >= 0)
238            break;
239        spin_unlock_irq(&ctx->wqh.lock);
240        cpu_relax();
241    }
242
243    /*
244     * If the timer is expired and it's periodic, we need to advance it
245     * because the caller may want to know the previous expiration time.
246     * We do not update "ticks" and "expired" since the timer will be
247     * re-programmed again in the following timerfd_setup() call.
248     */
249    if (ctx->expired && ctx->tintv.tv64)
250        hrtimer_forward_now(&ctx->tmr, ctx->tintv);
251
252    kotmr.it_value = ktime_to_timespec(timerfd_get_remaining(ctx));
253    kotmr.it_interval = ktime_to_timespec(ctx->tintv);
254
255    /*
256     * Re-program the timer to the new value ...
257     */
258    timerfd_setup(ctx, flags, &ktmr);
259
260    spin_unlock_irq(&ctx->wqh.lock);
261    fput(file);
262    if (otmr && copy_to_user(otmr, &kotmr, sizeof(kotmr)))
263        return -EFAULT;
264
265    return 0;
266}
267
268SYSCALL_DEFINE2(timerfd_gettime, int, ufd, struct itimerspec __user *, otmr)
269{
270    struct file *file;
271    struct timerfd_ctx *ctx;
272    struct itimerspec kotmr;
273
274    file = timerfd_fget(ufd);
275    if (IS_ERR(file))
276        return PTR_ERR(file);
277    ctx = file->private_data;
278
279    spin_lock_irq(&ctx->wqh.lock);
280    if (ctx->expired && ctx->tintv.tv64) {
281        ctx->expired = 0;
282        ctx->ticks +=
283            hrtimer_forward_now(&ctx->tmr, ctx->tintv) - 1;
284        hrtimer_restart(&ctx->tmr);
285    }
286    kotmr.it_value = ktime_to_timespec(timerfd_get_remaining(ctx));
287    kotmr.it_interval = ktime_to_timespec(ctx->tintv);
288    spin_unlock_irq(&ctx->wqh.lock);
289    fput(file);
290
291    return copy_to_user(otmr, &kotmr, sizeof(kotmr)) ? -EFAULT: 0;
292}
293
294

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