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e1ad7468 DL |
1 | /* |
2 | * fs/eventfd.c | |
3 | * | |
4 | * Copyright (C) 2007 Davide Libenzi <davidel@xmailserver.org> | |
5 | * | |
6 | */ | |
7 | ||
8 | #include <linux/file.h> | |
9 | #include <linux/poll.h> | |
10 | #include <linux/init.h> | |
11 | #include <linux/fs.h> | |
12 | #include <linux/sched.h> | |
13 | #include <linux/kernel.h> | |
14 | #include <linux/list.h> | |
15 | #include <linux/spinlock.h> | |
16 | #include <linux/anon_inodes.h> | |
7747cdb2 | 17 | #include <linux/syscalls.h> |
5718607b | 18 | #include <linux/module.h> |
13389010 DL |
19 | #include <linux/kref.h> |
20 | #include <linux/eventfd.h> | |
e1ad7468 DL |
21 | |
22 | struct eventfd_ctx { | |
13389010 | 23 | struct kref kref; |
e1ad7468 DL |
24 | wait_queue_head_t wqh; |
25 | /* | |
26 | * Every time that a write(2) is performed on an eventfd, the | |
27 | * value of the __u64 being written is added to "count" and a | |
28 | * wakeup is performed on "wqh". A read(2) will return the "count" | |
29 | * value to userspace, and will reset "count" to zero. The kernel | |
13389010 | 30 | * side eventfd_signal() also, adds to the "count" counter and |
e1ad7468 DL |
31 | * issue a wakeup. |
32 | */ | |
33 | __u64 count; | |
bcd0b235 | 34 | unsigned int flags; |
e1ad7468 DL |
35 | }; |
36 | ||
13389010 DL |
37 | /** |
38 | * eventfd_signal - Adds @n to the eventfd counter. | |
39 | * @ctx: [in] Pointer to the eventfd context. | |
40 | * @n: [in] Value of the counter to be added to the eventfd internal counter. | |
41 | * The value cannot be negative. | |
42 | * | |
43 | * This function is supposed to be called by the kernel in paths that do not | |
44 | * allow sleeping. In this function we allow the counter to reach the ULLONG_MAX | |
45 | * value, and we signal this as overflow condition by returining a POLLERR | |
46 | * to poll(2). | |
47 | * | |
48 | * Returns @n in case of success, a non-negative number lower than @n in case | |
49 | * of overflow, or the following error codes: | |
50 | * | |
51 | * -EINVAL : The value of @n is negative. | |
e1ad7468 | 52 | */ |
13389010 | 53 | int eventfd_signal(struct eventfd_ctx *ctx, int n) |
e1ad7468 | 54 | { |
e1ad7468 DL |
55 | unsigned long flags; |
56 | ||
57 | if (n < 0) | |
58 | return -EINVAL; | |
d48eb233 | 59 | spin_lock_irqsave(&ctx->wqh.lock, flags); |
e1ad7468 DL |
60 | if (ULLONG_MAX - ctx->count < n) |
61 | n = (int) (ULLONG_MAX - ctx->count); | |
62 | ctx->count += n; | |
63 | if (waitqueue_active(&ctx->wqh)) | |
39510888 | 64 | wake_up_locked_poll(&ctx->wqh, POLLIN); |
d48eb233 | 65 | spin_unlock_irqrestore(&ctx->wqh.lock, flags); |
e1ad7468 DL |
66 | |
67 | return n; | |
68 | } | |
5718607b | 69 | EXPORT_SYMBOL_GPL(eventfd_signal); |
e1ad7468 | 70 | |
562787a5 DL |
71 | static void eventfd_free_ctx(struct eventfd_ctx *ctx) |
72 | { | |
73 | kfree(ctx); | |
74 | } | |
75 | ||
13389010 DL |
76 | static void eventfd_free(struct kref *kref) |
77 | { | |
78 | struct eventfd_ctx *ctx = container_of(kref, struct eventfd_ctx, kref); | |
79 | ||
562787a5 | 80 | eventfd_free_ctx(ctx); |
13389010 DL |
81 | } |
82 | ||
83 | /** | |
84 | * eventfd_ctx_get - Acquires a reference to the internal eventfd context. | |
85 | * @ctx: [in] Pointer to the eventfd context. | |
86 | * | |
87 | * Returns: In case of success, returns a pointer to the eventfd context. | |
88 | */ | |
89 | struct eventfd_ctx *eventfd_ctx_get(struct eventfd_ctx *ctx) | |
90 | { | |
91 | kref_get(&ctx->kref); | |
92 | return ctx; | |
93 | } | |
94 | EXPORT_SYMBOL_GPL(eventfd_ctx_get); | |
95 | ||
96 | /** | |
97 | * eventfd_ctx_put - Releases a reference to the internal eventfd context. | |
98 | * @ctx: [in] Pointer to eventfd context. | |
99 | * | |
100 | * The eventfd context reference must have been previously acquired either | |
101 | * with eventfd_ctx_get() or eventfd_ctx_fdget()). | |
102 | */ | |
103 | void eventfd_ctx_put(struct eventfd_ctx *ctx) | |
104 | { | |
105 | kref_put(&ctx->kref, eventfd_free); | |
106 | } | |
107 | EXPORT_SYMBOL_GPL(eventfd_ctx_put); | |
108 | ||
e1ad7468 DL |
109 | static int eventfd_release(struct inode *inode, struct file *file) |
110 | { | |
13389010 DL |
111 | struct eventfd_ctx *ctx = file->private_data; |
112 | ||
113 | wake_up_poll(&ctx->wqh, POLLHUP); | |
114 | eventfd_ctx_put(ctx); | |
e1ad7468 DL |
115 | return 0; |
116 | } | |
117 | ||
118 | static unsigned int eventfd_poll(struct file *file, poll_table *wait) | |
119 | { | |
120 | struct eventfd_ctx *ctx = file->private_data; | |
121 | unsigned int events = 0; | |
122 | unsigned long flags; | |
123 | ||
124 | poll_wait(file, &ctx->wqh, wait); | |
125 | ||
d48eb233 | 126 | spin_lock_irqsave(&ctx->wqh.lock, flags); |
e1ad7468 DL |
127 | if (ctx->count > 0) |
128 | events |= POLLIN; | |
129 | if (ctx->count == ULLONG_MAX) | |
130 | events |= POLLERR; | |
131 | if (ULLONG_MAX - 1 > ctx->count) | |
132 | events |= POLLOUT; | |
d48eb233 | 133 | spin_unlock_irqrestore(&ctx->wqh.lock, flags); |
e1ad7468 DL |
134 | |
135 | return events; | |
136 | } | |
137 | ||
cb289d62 DL |
138 | static void eventfd_ctx_do_read(struct eventfd_ctx *ctx, __u64 *cnt) |
139 | { | |
140 | *cnt = (ctx->flags & EFD_SEMAPHORE) ? 1 : ctx->count; | |
141 | ctx->count -= *cnt; | |
142 | } | |
143 | ||
144 | /** | |
145 | * eventfd_ctx_remove_wait_queue - Read the current counter and removes wait queue. | |
146 | * @ctx: [in] Pointer to eventfd context. | |
147 | * @wait: [in] Wait queue to be removed. | |
148 | * @cnt: [out] Pointer to the 64bit conter value. | |
149 | * | |
150 | * Returns zero if successful, or the following error codes: | |
151 | * | |
152 | * -EAGAIN : The operation would have blocked. | |
153 | * | |
154 | * This is used to atomically remove a wait queue entry from the eventfd wait | |
155 | * queue head, and read/reset the counter value. | |
156 | */ | |
157 | int eventfd_ctx_remove_wait_queue(struct eventfd_ctx *ctx, wait_queue_t *wait, | |
158 | __u64 *cnt) | |
159 | { | |
160 | unsigned long flags; | |
161 | ||
162 | spin_lock_irqsave(&ctx->wqh.lock, flags); | |
163 | eventfd_ctx_do_read(ctx, cnt); | |
164 | __remove_wait_queue(&ctx->wqh, wait); | |
165 | if (*cnt != 0 && waitqueue_active(&ctx->wqh)) | |
166 | wake_up_locked_poll(&ctx->wqh, POLLOUT); | |
167 | spin_unlock_irqrestore(&ctx->wqh.lock, flags); | |
168 | ||
169 | return *cnt != 0 ? 0 : -EAGAIN; | |
170 | } | |
171 | EXPORT_SYMBOL_GPL(eventfd_ctx_remove_wait_queue); | |
172 | ||
173 | /** | |
174 | * eventfd_ctx_read - Reads the eventfd counter or wait if it is zero. | |
175 | * @ctx: [in] Pointer to eventfd context. | |
176 | * @no_wait: [in] Different from zero if the operation should not block. | |
177 | * @cnt: [out] Pointer to the 64bit conter value. | |
178 | * | |
179 | * Returns zero if successful, or the following error codes: | |
180 | * | |
181 | * -EAGAIN : The operation would have blocked but @no_wait was nonzero. | |
182 | * -ERESTARTSYS : A signal interrupted the wait operation. | |
183 | * | |
184 | * If @no_wait is zero, the function might sleep until the eventfd internal | |
185 | * counter becomes greater than zero. | |
186 | */ | |
187 | ssize_t eventfd_ctx_read(struct eventfd_ctx *ctx, int no_wait, __u64 *cnt) | |
e1ad7468 | 188 | { |
e1ad7468 | 189 | ssize_t res; |
e1ad7468 DL |
190 | DECLARE_WAITQUEUE(wait, current); |
191 | ||
d48eb233 | 192 | spin_lock_irq(&ctx->wqh.lock); |
cb289d62 | 193 | *cnt = 0; |
e1ad7468 | 194 | res = -EAGAIN; |
bcd0b235 | 195 | if (ctx->count > 0) |
cb289d62 DL |
196 | res = 0; |
197 | else if (!no_wait) { | |
e1ad7468 | 198 | __add_wait_queue(&ctx->wqh, &wait); |
cb289d62 | 199 | for (;;) { |
e1ad7468 DL |
200 | set_current_state(TASK_INTERRUPTIBLE); |
201 | if (ctx->count > 0) { | |
cb289d62 | 202 | res = 0; |
e1ad7468 DL |
203 | break; |
204 | } | |
205 | if (signal_pending(current)) { | |
206 | res = -ERESTARTSYS; | |
207 | break; | |
208 | } | |
d48eb233 | 209 | spin_unlock_irq(&ctx->wqh.lock); |
e1ad7468 | 210 | schedule(); |
d48eb233 | 211 | spin_lock_irq(&ctx->wqh.lock); |
e1ad7468 DL |
212 | } |
213 | __remove_wait_queue(&ctx->wqh, &wait); | |
214 | __set_current_state(TASK_RUNNING); | |
215 | } | |
cb289d62 DL |
216 | if (likely(res == 0)) { |
217 | eventfd_ctx_do_read(ctx, cnt); | |
e1ad7468 | 218 | if (waitqueue_active(&ctx->wqh)) |
39510888 | 219 | wake_up_locked_poll(&ctx->wqh, POLLOUT); |
e1ad7468 | 220 | } |
d48eb233 | 221 | spin_unlock_irq(&ctx->wqh.lock); |
e1ad7468 DL |
222 | |
223 | return res; | |
224 | } | |
cb289d62 DL |
225 | EXPORT_SYMBOL_GPL(eventfd_ctx_read); |
226 | ||
227 | static ssize_t eventfd_read(struct file *file, char __user *buf, size_t count, | |
228 | loff_t *ppos) | |
229 | { | |
230 | struct eventfd_ctx *ctx = file->private_data; | |
231 | ssize_t res; | |
232 | __u64 cnt; | |
233 | ||
234 | if (count < sizeof(cnt)) | |
235 | return -EINVAL; | |
236 | res = eventfd_ctx_read(ctx, file->f_flags & O_NONBLOCK, &cnt); | |
237 | if (res < 0) | |
238 | return res; | |
239 | ||
240 | return put_user(cnt, (__u64 __user *) buf) ? -EFAULT : sizeof(cnt); | |
241 | } | |
e1ad7468 DL |
242 | |
243 | static ssize_t eventfd_write(struct file *file, const char __user *buf, size_t count, | |
244 | loff_t *ppos) | |
245 | { | |
246 | struct eventfd_ctx *ctx = file->private_data; | |
247 | ssize_t res; | |
248 | __u64 ucnt; | |
249 | DECLARE_WAITQUEUE(wait, current); | |
250 | ||
251 | if (count < sizeof(ucnt)) | |
252 | return -EINVAL; | |
253 | if (copy_from_user(&ucnt, buf, sizeof(ucnt))) | |
254 | return -EFAULT; | |
255 | if (ucnt == ULLONG_MAX) | |
256 | return -EINVAL; | |
d48eb233 | 257 | spin_lock_irq(&ctx->wqh.lock); |
e1ad7468 DL |
258 | res = -EAGAIN; |
259 | if (ULLONG_MAX - ctx->count > ucnt) | |
260 | res = sizeof(ucnt); | |
261 | else if (!(file->f_flags & O_NONBLOCK)) { | |
262 | __add_wait_queue(&ctx->wqh, &wait); | |
263 | for (res = 0;;) { | |
264 | set_current_state(TASK_INTERRUPTIBLE); | |
265 | if (ULLONG_MAX - ctx->count > ucnt) { | |
266 | res = sizeof(ucnt); | |
267 | break; | |
268 | } | |
269 | if (signal_pending(current)) { | |
270 | res = -ERESTARTSYS; | |
271 | break; | |
272 | } | |
d48eb233 | 273 | spin_unlock_irq(&ctx->wqh.lock); |
e1ad7468 | 274 | schedule(); |
d48eb233 | 275 | spin_lock_irq(&ctx->wqh.lock); |
e1ad7468 DL |
276 | } |
277 | __remove_wait_queue(&ctx->wqh, &wait); | |
278 | __set_current_state(TASK_RUNNING); | |
279 | } | |
bcd0b235 | 280 | if (likely(res > 0)) { |
e1ad7468 DL |
281 | ctx->count += ucnt; |
282 | if (waitqueue_active(&ctx->wqh)) | |
39510888 | 283 | wake_up_locked_poll(&ctx->wqh, POLLIN); |
e1ad7468 | 284 | } |
d48eb233 | 285 | spin_unlock_irq(&ctx->wqh.lock); |
e1ad7468 DL |
286 | |
287 | return res; | |
288 | } | |
289 | ||
290 | static const struct file_operations eventfd_fops = { | |
291 | .release = eventfd_release, | |
292 | .poll = eventfd_poll, | |
293 | .read = eventfd_read, | |
294 | .write = eventfd_write, | |
295 | }; | |
296 | ||
13389010 DL |
297 | /** |
298 | * eventfd_fget - Acquire a reference of an eventfd file descriptor. | |
299 | * @fd: [in] Eventfd file descriptor. | |
300 | * | |
301 | * Returns a pointer to the eventfd file structure in case of success, or the | |
302 | * following error pointer: | |
303 | * | |
304 | * -EBADF : Invalid @fd file descriptor. | |
305 | * -EINVAL : The @fd file descriptor is not an eventfd file. | |
306 | */ | |
e1ad7468 DL |
307 | struct file *eventfd_fget(int fd) |
308 | { | |
309 | struct file *file; | |
310 | ||
311 | file = fget(fd); | |
312 | if (!file) | |
313 | return ERR_PTR(-EBADF); | |
314 | if (file->f_op != &eventfd_fops) { | |
315 | fput(file); | |
316 | return ERR_PTR(-EINVAL); | |
317 | } | |
318 | ||
319 | return file; | |
320 | } | |
5718607b | 321 | EXPORT_SYMBOL_GPL(eventfd_fget); |
e1ad7468 | 322 | |
13389010 DL |
323 | /** |
324 | * eventfd_ctx_fdget - Acquires a reference to the internal eventfd context. | |
325 | * @fd: [in] Eventfd file descriptor. | |
326 | * | |
327 | * Returns a pointer to the internal eventfd context, otherwise the error | |
328 | * pointers returned by the following functions: | |
329 | * | |
330 | * eventfd_fget | |
331 | */ | |
332 | struct eventfd_ctx *eventfd_ctx_fdget(int fd) | |
333 | { | |
334 | struct file *file; | |
335 | struct eventfd_ctx *ctx; | |
336 | ||
337 | file = eventfd_fget(fd); | |
338 | if (IS_ERR(file)) | |
339 | return (struct eventfd_ctx *) file; | |
340 | ctx = eventfd_ctx_get(file->private_data); | |
341 | fput(file); | |
342 | ||
343 | return ctx; | |
344 | } | |
345 | EXPORT_SYMBOL_GPL(eventfd_ctx_fdget); | |
346 | ||
347 | /** | |
348 | * eventfd_ctx_fileget - Acquires a reference to the internal eventfd context. | |
349 | * @file: [in] Eventfd file pointer. | |
350 | * | |
351 | * Returns a pointer to the internal eventfd context, otherwise the error | |
352 | * pointer: | |
353 | * | |
354 | * -EINVAL : The @fd file descriptor is not an eventfd file. | |
355 | */ | |
356 | struct eventfd_ctx *eventfd_ctx_fileget(struct file *file) | |
357 | { | |
358 | if (file->f_op != &eventfd_fops) | |
359 | return ERR_PTR(-EINVAL); | |
360 | ||
361 | return eventfd_ctx_get(file->private_data); | |
362 | } | |
363 | EXPORT_SYMBOL_GPL(eventfd_ctx_fileget); | |
364 | ||
562787a5 DL |
365 | /** |
366 | * eventfd_file_create - Creates an eventfd file pointer. | |
367 | * @count: Initial eventfd counter value. | |
368 | * @flags: Flags for the eventfd file. | |
369 | * | |
370 | * This function creates an eventfd file pointer, w/out installing it into | |
371 | * the fd table. This is useful when the eventfd file is used during the | |
372 | * initialization of data structures that require extra setup after the eventfd | |
373 | * creation. So the eventfd creation is split into the file pointer creation | |
374 | * phase, and the file descriptor installation phase. | |
375 | * In this way races with userspace closing the newly installed file descriptor | |
376 | * can be avoided. | |
377 | * Returns an eventfd file pointer, or a proper error pointer. | |
378 | */ | |
379 | struct file *eventfd_file_create(unsigned int count, int flags) | |
e1ad7468 | 380 | { |
562787a5 | 381 | struct file *file; |
e1ad7468 | 382 | struct eventfd_ctx *ctx; |
e1ad7468 | 383 | |
e38b36f3 UD |
384 | /* Check the EFD_* constants for consistency. */ |
385 | BUILD_BUG_ON(EFD_CLOEXEC != O_CLOEXEC); | |
386 | BUILD_BUG_ON(EFD_NONBLOCK != O_NONBLOCK); | |
387 | ||
bcd0b235 | 388 | if (flags & ~EFD_FLAGS_SET) |
562787a5 | 389 | return ERR_PTR(-EINVAL); |
b087498e | 390 | |
e1ad7468 DL |
391 | ctx = kmalloc(sizeof(*ctx), GFP_KERNEL); |
392 | if (!ctx) | |
562787a5 | 393 | return ERR_PTR(-ENOMEM); |
e1ad7468 | 394 | |
13389010 | 395 | kref_init(&ctx->kref); |
e1ad7468 | 396 | init_waitqueue_head(&ctx->wqh); |
e1ad7468 | 397 | ctx->count = count; |
bcd0b235 | 398 | ctx->flags = flags; |
e1ad7468 | 399 | |
562787a5 | 400 | file = anon_inode_getfile("[eventfd]", &eventfd_fops, ctx, |
628ff7c1 | 401 | O_RDWR | (flags & EFD_SHARED_FCNTL_FLAGS)); |
562787a5 DL |
402 | if (IS_ERR(file)) |
403 | eventfd_free_ctx(ctx); | |
404 | ||
405 | return file; | |
406 | } | |
407 | ||
408 | SYSCALL_DEFINE2(eventfd2, unsigned int, count, int, flags) | |
409 | { | |
410 | int fd, error; | |
411 | struct file *file; | |
412 | ||
413 | error = get_unused_fd_flags(flags & EFD_SHARED_FCNTL_FLAGS); | |
414 | if (error < 0) | |
415 | return error; | |
416 | fd = error; | |
417 | ||
418 | file = eventfd_file_create(count, flags); | |
419 | if (IS_ERR(file)) { | |
420 | error = PTR_ERR(file); | |
421 | goto err_put_unused_fd; | |
422 | } | |
423 | fd_install(fd, file); | |
424 | ||
2030a42c | 425 | return fd; |
562787a5 DL |
426 | |
427 | err_put_unused_fd: | |
428 | put_unused_fd(fd); | |
429 | ||
430 | return error; | |
e1ad7468 DL |
431 | } |
432 | ||
d4e82042 | 433 | SYSCALL_DEFINE1(eventfd, unsigned int, count) |
b087498e UD |
434 | { |
435 | return sys_eventfd2(count, 0); | |
436 | } | |
bcd0b235 | 437 |