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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>
5a0e3ad6 17#include <linux/slab.h>
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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>
45cc2b96 24#include <linux/syscalls.h>
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25
26struct timerfd_ctx {
27 struct hrtimer tmr;
28 ktime_t tintv;
b215e283 29 wait_queue_head_t wqh;
4d672e7a 30 u64 ticks;
b215e283 31 int expired;
4d672e7a 32 int clockid;
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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,
4d672e7a 38 * tintv.tv64 != 0) until the timer is accessed.
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39 */
40static 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
18963c01 45 spin_lock_irqsave(&ctx->wqh.lock, flags);
b215e283 46 ctx->expired = 1;
4d672e7a 47 ctx->ticks++;
b215e283 48 wake_up_locked(&ctx->wqh);
18963c01 49 spin_unlock_irqrestore(&ctx->wqh.lock, flags);
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50
51 return HRTIMER_NORESTART;
52}
53
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54static ktime_t timerfd_get_remaining(struct timerfd_ctx *ctx)
55{
76369470 56 ktime_t remaining;
4d672e7a 57
76369470 58 remaining = hrtimer_expires_remaining(&ctx->tmr);
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59 return remaining.tv64 < 0 ? ktime_set(0, 0): remaining;
60}
61
62static void timerfd_setup(struct timerfd_ctx *ctx, int flags,
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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;
4d672e7a 73 ctx->ticks = 0;
b215e283 74 ctx->tintv = timespec_to_ktime(ktmr->it_interval);
4d672e7a 75 hrtimer_init(&ctx->tmr, ctx->clockid, htmode);
76369470 76 hrtimer_set_expires(&ctx->tmr, texp);
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77 ctx->tmr.function = timerfd_tmrproc;
78 if (texp.tv64 != 0)
79 hrtimer_start(&ctx->tmr, texp, htmode);
80}
81
82static 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
91static 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
18963c01 99 spin_lock_irqsave(&ctx->wqh.lock, flags);
4d672e7a 100 if (ctx->ticks)
b215e283 101 events |= POLLIN;
18963c01 102 spin_unlock_irqrestore(&ctx->wqh.lock, flags);
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103
104 return events;
105}
106
107static 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;
09828402 112 u64 ticks = 0;
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113
114 if (count < sizeof(ticks))
115 return -EINVAL;
18963c01 116 spin_lock_irq(&ctx->wqh.lock);
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117 if (file->f_flags & O_NONBLOCK)
118 res = -EAGAIN;
119 else
120 res = wait_event_interruptible_locked_irq(ctx->wqh, ctx->ticks);
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121 if (ctx->ticks) {
122 ticks = ctx->ticks;
123 if (ctx->expired && ctx->tintv.tv64) {
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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 */
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130 ticks += hrtimer_forward_now(&ctx->tmr,
131 ctx->tintv) - 1;
b215e283 132 hrtimer_restart(&ctx->tmr);
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133 }
134 ctx->expired = 0;
135 ctx->ticks = 0;
b215e283 136 }
18963c01 137 spin_unlock_irq(&ctx->wqh.lock);
b215e283 138 if (ticks)
09828402 139 res = put_user(ticks, (u64 __user *) buf) ? -EFAULT: sizeof(ticks);
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140 return res;
141}
142
143static const struct file_operations timerfd_fops = {
144 .release = timerfd_release,
145 .poll = timerfd_poll,
146 .read = timerfd_read,
147};
148
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149static struct file *timerfd_fget(int fd)
150{
151 struct file *file;
152
153 file = fget(fd);
154 if (!file)
155 return ERR_PTR(-EBADF);
156 if (file->f_op != &timerfd_fops) {
157 fput(file);
158 return ERR_PTR(-EINVAL);
159 }
160
161 return file;
162}
163
836f92ad 164SYSCALL_DEFINE2(timerfd_create, int, clockid, int, flags)
b215e283 165{
2030a42c 166 int ufd;
b215e283 167 struct timerfd_ctx *ctx;
b215e283 168
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169 /* Check the TFD_* constants for consistency. */
170 BUILD_BUG_ON(TFD_CLOEXEC != O_CLOEXEC);
171 BUILD_BUG_ON(TFD_NONBLOCK != O_NONBLOCK);
172
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173 if ((flags & ~TFD_CREATE_FLAGS) ||
174 (clockid != CLOCK_MONOTONIC &&
175 clockid != CLOCK_REALTIME))
b215e283 176 return -EINVAL;
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177
178 ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
179 if (!ctx)
180 return -ENOMEM;
181
182 init_waitqueue_head(&ctx->wqh);
183 ctx->clockid = clockid;
184 hrtimer_init(&ctx->tmr, clockid, HRTIMER_MODE_ABS);
185
11fcb6c1 186 ufd = anon_inode_getfd("[timerfd]", &timerfd_fops, ctx,
628ff7c1 187 O_RDWR | (flags & TFD_SHARED_FCNTL_FLAGS));
2030a42c 188 if (ufd < 0)
4d672e7a 189 kfree(ctx);
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190
191 return ufd;
192}
193
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194SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
195 const struct itimerspec __user *, utmr,
196 struct itimerspec __user *, otmr)
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197{
198 struct file *file;
199 struct timerfd_ctx *ctx;
200 struct itimerspec ktmr, kotmr;
201
202 if (copy_from_user(&ktmr, utmr, sizeof(ktmr)))
203 return -EFAULT;
204
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205 if ((flags & ~TFD_SETTIME_FLAGS) ||
206 !timespec_valid(&ktmr.it_value) ||
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207 !timespec_valid(&ktmr.it_interval))
208 return -EINVAL;
209
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210 file = timerfd_fget(ufd);
211 if (IS_ERR(file))
212 return PTR_ERR(file);
213 ctx = file->private_data;
b215e283 214
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215 /*
216 * We need to stop the existing timer before reprogramming
217 * it to the new values.
218 */
219 for (;;) {
220 spin_lock_irq(&ctx->wqh.lock);
221 if (hrtimer_try_to_cancel(&ctx->tmr) >= 0)
222 break;
18963c01 223 spin_unlock_irq(&ctx->wqh.lock);
4d672e7a 224 cpu_relax();
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225 }
226
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227 /*
228 * If the timer is expired and it's periodic, we need to advance it
229 * because the caller may want to know the previous expiration time.
230 * We do not update "ticks" and "expired" since the timer will be
231 * re-programmed again in the following timerfd_setup() call.
232 */
233 if (ctx->expired && ctx->tintv.tv64)
234 hrtimer_forward_now(&ctx->tmr, ctx->tintv);
b215e283 235
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236 kotmr.it_value = ktime_to_timespec(timerfd_get_remaining(ctx));
237 kotmr.it_interval = ktime_to_timespec(ctx->tintv);
238
239 /*
240 * Re-program the timer to the new value ...
241 */
242 timerfd_setup(ctx, flags, &ktmr);
243
244 spin_unlock_irq(&ctx->wqh.lock);
245 fput(file);
246 if (otmr && copy_to_user(otmr, &kotmr, sizeof(kotmr)))
247 return -EFAULT;
248
249 return 0;
250}
251
d4e82042 252SYSCALL_DEFINE2(timerfd_gettime, int, ufd, struct itimerspec __user *, otmr)
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253{
254 struct file *file;
255 struct timerfd_ctx *ctx;
256 struct itimerspec kotmr;
257
258 file = timerfd_fget(ufd);
259 if (IS_ERR(file))
260 return PTR_ERR(file);
261 ctx = file->private_data;
262
263 spin_lock_irq(&ctx->wqh.lock);
264 if (ctx->expired && ctx->tintv.tv64) {
265 ctx->expired = 0;
266 ctx->ticks +=
267 hrtimer_forward_now(&ctx->tmr, ctx->tintv) - 1;
268 hrtimer_restart(&ctx->tmr);
269 }
270 kotmr.it_value = ktime_to_timespec(timerfd_get_remaining(ctx));
271 kotmr.it_interval = ktime_to_timespec(ctx->tintv);
272 spin_unlock_irq(&ctx->wqh.lock);
273 fput(file);
274
275 return copy_to_user(otmr, &kotmr, sizeof(kotmr)) ? -EFAULT: 0;
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276}
277