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