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b215e283 DL |
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 | ||
24 | struct timerfd_ctx { | |
25 | struct hrtimer tmr; | |
26 | ktime_t tintv; | |
27 | spinlock_t lock; | |
28 | wait_queue_head_t wqh; | |
29 | int expired; | |
30 | }; | |
31 | ||
32 | /* | |
33 | * This gets called when the timer event triggers. We set the "expired" | |
34 | * flag, but we do not re-arm the timer (in case it's necessary, | |
35 | * tintv.tv64 != 0) until the timer is read. | |
36 | */ | |
37 | static enum hrtimer_restart timerfd_tmrproc(struct hrtimer *htmr) | |
38 | { | |
39 | struct timerfd_ctx *ctx = container_of(htmr, struct timerfd_ctx, tmr); | |
40 | unsigned long flags; | |
41 | ||
42 | spin_lock_irqsave(&ctx->lock, flags); | |
43 | ctx->expired = 1; | |
44 | wake_up_locked(&ctx->wqh); | |
45 | spin_unlock_irqrestore(&ctx->lock, flags); | |
46 | ||
47 | return HRTIMER_NORESTART; | |
48 | } | |
49 | ||
50 | static void timerfd_setup(struct timerfd_ctx *ctx, int clockid, int flags, | |
51 | const struct itimerspec *ktmr) | |
52 | { | |
53 | enum hrtimer_mode htmode; | |
54 | ktime_t texp; | |
55 | ||
56 | htmode = (flags & TFD_TIMER_ABSTIME) ? | |
57 | HRTIMER_MODE_ABS: HRTIMER_MODE_REL; | |
58 | ||
59 | texp = timespec_to_ktime(ktmr->it_value); | |
60 | ctx->expired = 0; | |
61 | ctx->tintv = timespec_to_ktime(ktmr->it_interval); | |
62 | hrtimer_init(&ctx->tmr, clockid, htmode); | |
63 | ctx->tmr.expires = texp; | |
64 | ctx->tmr.function = timerfd_tmrproc; | |
65 | if (texp.tv64 != 0) | |
66 | hrtimer_start(&ctx->tmr, texp, htmode); | |
67 | } | |
68 | ||
69 | static int timerfd_release(struct inode *inode, struct file *file) | |
70 | { | |
71 | struct timerfd_ctx *ctx = file->private_data; | |
72 | ||
73 | hrtimer_cancel(&ctx->tmr); | |
74 | kfree(ctx); | |
75 | return 0; | |
76 | } | |
77 | ||
78 | static unsigned int timerfd_poll(struct file *file, poll_table *wait) | |
79 | { | |
80 | struct timerfd_ctx *ctx = file->private_data; | |
81 | unsigned int events = 0; | |
82 | unsigned long flags; | |
83 | ||
84 | poll_wait(file, &ctx->wqh, wait); | |
85 | ||
86 | spin_lock_irqsave(&ctx->lock, flags); | |
87 | if (ctx->expired) | |
88 | events |= POLLIN; | |
89 | spin_unlock_irqrestore(&ctx->lock, flags); | |
90 | ||
91 | return events; | |
92 | } | |
93 | ||
94 | static ssize_t timerfd_read(struct file *file, char __user *buf, size_t count, | |
95 | loff_t *ppos) | |
96 | { | |
97 | struct timerfd_ctx *ctx = file->private_data; | |
98 | ssize_t res; | |
99 | u32 ticks = 0; | |
100 | DECLARE_WAITQUEUE(wait, current); | |
101 | ||
102 | if (count < sizeof(ticks)) | |
103 | return -EINVAL; | |
104 | spin_lock_irq(&ctx->lock); | |
105 | res = -EAGAIN; | |
106 | if (!ctx->expired && !(file->f_flags & O_NONBLOCK)) { | |
107 | __add_wait_queue(&ctx->wqh, &wait); | |
108 | for (res = 0;;) { | |
109 | set_current_state(TASK_INTERRUPTIBLE); | |
110 | if (ctx->expired) { | |
111 | res = 0; | |
112 | break; | |
113 | } | |
114 | if (signal_pending(current)) { | |
115 | res = -ERESTARTSYS; | |
116 | break; | |
117 | } | |
118 | spin_unlock_irq(&ctx->lock); | |
119 | schedule(); | |
120 | spin_lock_irq(&ctx->lock); | |
121 | } | |
122 | __remove_wait_queue(&ctx->wqh, &wait); | |
123 | __set_current_state(TASK_RUNNING); | |
124 | } | |
125 | if (ctx->expired) { | |
126 | ctx->expired = 0; | |
127 | if (ctx->tintv.tv64 != 0) { | |
128 | /* | |
129 | * If tintv.tv64 != 0, this is a periodic timer that | |
130 | * needs to be re-armed. We avoid doing it in the timer | |
131 | * callback to avoid DoS attacks specifying a very | |
132 | * short timer period. | |
133 | */ | |
134 | ticks = (u32) | |
135 | hrtimer_forward(&ctx->tmr, | |
136 | hrtimer_cb_get_time(&ctx->tmr), | |
137 | ctx->tintv); | |
138 | hrtimer_restart(&ctx->tmr); | |
139 | } else | |
140 | ticks = 1; | |
141 | } | |
142 | spin_unlock_irq(&ctx->lock); | |
143 | if (ticks) | |
144 | res = put_user(ticks, buf) ? -EFAULT: sizeof(ticks); | |
145 | return res; | |
146 | } | |
147 | ||
148 | static const struct file_operations timerfd_fops = { | |
149 | .release = timerfd_release, | |
150 | .poll = timerfd_poll, | |
151 | .read = timerfd_read, | |
152 | }; | |
153 | ||
154 | asmlinkage long sys_timerfd(int ufd, int clockid, int flags, | |
155 | const struct itimerspec __user *utmr) | |
156 | { | |
157 | int error; | |
158 | struct timerfd_ctx *ctx; | |
159 | struct file *file; | |
160 | struct inode *inode; | |
161 | struct itimerspec ktmr; | |
162 | ||
163 | if (copy_from_user(&ktmr, utmr, sizeof(ktmr))) | |
164 | return -EFAULT; | |
165 | ||
166 | if (clockid != CLOCK_MONOTONIC && | |
167 | clockid != CLOCK_REALTIME) | |
168 | return -EINVAL; | |
169 | if (!timespec_valid(&ktmr.it_value) || | |
170 | !timespec_valid(&ktmr.it_interval)) | |
171 | return -EINVAL; | |
172 | ||
173 | if (ufd == -1) { | |
174 | ctx = kmalloc(sizeof(*ctx), GFP_KERNEL); | |
175 | if (!ctx) | |
176 | return -ENOMEM; | |
177 | ||
178 | init_waitqueue_head(&ctx->wqh); | |
179 | spin_lock_init(&ctx->lock); | |
180 | ||
181 | timerfd_setup(ctx, clockid, flags, &ktmr); | |
182 | ||
183 | /* | |
184 | * When we call this, the initialization must be complete, since | |
185 | * anon_inode_getfd() will install the fd. | |
186 | */ | |
187 | error = anon_inode_getfd(&ufd, &inode, &file, "[timerfd]", | |
188 | &timerfd_fops, ctx); | |
189 | if (error) | |
190 | goto err_tmrcancel; | |
191 | } else { | |
192 | file = fget(ufd); | |
193 | if (!file) | |
194 | return -EBADF; | |
195 | ctx = file->private_data; | |
196 | if (file->f_op != &timerfd_fops) { | |
197 | fput(file); | |
198 | return -EINVAL; | |
199 | } | |
200 | /* | |
201 | * We need to stop the existing timer before reprogramming | |
202 | * it to the new values. | |
203 | */ | |
204 | for (;;) { | |
205 | spin_lock_irq(&ctx->lock); | |
206 | if (hrtimer_try_to_cancel(&ctx->tmr) >= 0) | |
207 | break; | |
208 | spin_unlock_irq(&ctx->lock); | |
209 | cpu_relax(); | |
210 | } | |
211 | /* | |
212 | * Re-program the timer to the new value ... | |
213 | */ | |
214 | timerfd_setup(ctx, clockid, flags, &ktmr); | |
215 | ||
216 | spin_unlock_irq(&ctx->lock); | |
217 | fput(file); | |
218 | } | |
219 | ||
220 | return ufd; | |
221 | ||
222 | err_tmrcancel: | |
223 | hrtimer_cancel(&ctx->tmr); | |
224 | kfree(ctx); | |
225 | return error; | |
226 | } | |
227 |