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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 | |
279 |
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