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
25 struct 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 */
39 static 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
53 static 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
61 static 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
81 static 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
90 static 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
106 static 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
159 static const struct file_operations timerfd_fops = {
160 .release = timerfd_release,
161 .poll = timerfd_poll,
162 .read = timerfd_read,
163 };
164
165 static 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
180 SYSCALL_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
210 SYSCALL_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
268 SYSCALL_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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