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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/slab.h> |
15 | #include <linux/list.h> |
16 | #include <linux/spinlock.h> |
17 | #include <linux/anon_inodes.h> |
18 | #include <linux/syscalls.h> |
19 | #include <linux/module.h> |
20 | #include <linux/kref.h> |
21 | #include <linux/eventfd.h> |
22 | |
23 | struct eventfd_ctx { |
24 | struct kref kref; |
25 | wait_queue_head_t wqh; |
26 | /* |
27 | * Every time that a write(2) is performed on an eventfd, the |
28 | * value of the __u64 being written is added to "count" and a |
29 | * wakeup is performed on "wqh". A read(2) will return the "count" |
30 | * value to userspace, and will reset "count" to zero. The kernel |
31 | * side eventfd_signal() also, adds to the "count" counter and |
32 | * issue a wakeup. |
33 | */ |
34 | __u64 count; |
35 | unsigned int flags; |
36 | }; |
37 | |
38 | /** |
39 | * eventfd_signal - Adds @n to the eventfd counter. |
40 | * @ctx: [in] Pointer to the eventfd context. |
41 | * @n: [in] Value of the counter to be added to the eventfd internal counter. |
42 | * The value cannot be negative. |
43 | * |
44 | * This function is supposed to be called by the kernel in paths that do not |
45 | * allow sleeping. In this function we allow the counter to reach the ULLONG_MAX |
46 | * value, and we signal this as overflow condition by returining a POLLERR |
47 | * to poll(2). |
48 | * |
49 | * Returns @n in case of success, a non-negative number lower than @n in case |
50 | * of overflow, or the following error codes: |
51 | * |
52 | * -EINVAL : The value of @n is negative. |
53 | */ |
54 | int eventfd_signal(struct eventfd_ctx *ctx, int n) |
55 | { |
56 | unsigned long flags; |
57 | |
58 | if (n < 0) |
59 | return -EINVAL; |
60 | spin_lock_irqsave(&ctx->wqh.lock, flags); |
61 | if (ULLONG_MAX - ctx->count < n) |
62 | n = (int) (ULLONG_MAX - ctx->count); |
63 | ctx->count += n; |
64 | if (waitqueue_active(&ctx->wqh)) |
65 | wake_up_locked_poll(&ctx->wqh, POLLIN); |
66 | spin_unlock_irqrestore(&ctx->wqh.lock, flags); |
67 | |
68 | return n; |
69 | } |
70 | EXPORT_SYMBOL_GPL(eventfd_signal); |
71 | |
72 | static void eventfd_free_ctx(struct eventfd_ctx *ctx) |
73 | { |
74 | kfree(ctx); |
75 | } |
76 | |
77 | static void eventfd_free(struct kref *kref) |
78 | { |
79 | struct eventfd_ctx *ctx = container_of(kref, struct eventfd_ctx, kref); |
80 | |
81 | eventfd_free_ctx(ctx); |
82 | } |
83 | |
84 | /** |
85 | * eventfd_ctx_get - Acquires a reference to the internal eventfd context. |
86 | * @ctx: [in] Pointer to the eventfd context. |
87 | * |
88 | * Returns: In case of success, returns a pointer to the eventfd context. |
89 | */ |
90 | struct eventfd_ctx *eventfd_ctx_get(struct eventfd_ctx *ctx) |
91 | { |
92 | kref_get(&ctx->kref); |
93 | return ctx; |
94 | } |
95 | EXPORT_SYMBOL_GPL(eventfd_ctx_get); |
96 | |
97 | /** |
98 | * eventfd_ctx_put - Releases a reference to the internal eventfd context. |
99 | * @ctx: [in] Pointer to eventfd context. |
100 | * |
101 | * The eventfd context reference must have been previously acquired either |
102 | * with eventfd_ctx_get() or eventfd_ctx_fdget(). |
103 | */ |
104 | void eventfd_ctx_put(struct eventfd_ctx *ctx) |
105 | { |
106 | kref_put(&ctx->kref, eventfd_free); |
107 | } |
108 | EXPORT_SYMBOL_GPL(eventfd_ctx_put); |
109 | |
110 | static int eventfd_release(struct inode *inode, struct file *file) |
111 | { |
112 | struct eventfd_ctx *ctx = file->private_data; |
113 | |
114 | wake_up_poll(&ctx->wqh, POLLHUP); |
115 | eventfd_ctx_put(ctx); |
116 | return 0; |
117 | } |
118 | |
119 | static unsigned int eventfd_poll(struct file *file, poll_table *wait) |
120 | { |
121 | struct eventfd_ctx *ctx = file->private_data; |
122 | unsigned int events = 0; |
123 | unsigned long flags; |
124 | |
125 | poll_wait(file, &ctx->wqh, wait); |
126 | |
127 | spin_lock_irqsave(&ctx->wqh.lock, flags); |
128 | if (ctx->count > 0) |
129 | events |= POLLIN; |
130 | if (ctx->count == ULLONG_MAX) |
131 | events |= POLLERR; |
132 | if (ULLONG_MAX - 1 > ctx->count) |
133 | events |= POLLOUT; |
134 | spin_unlock_irqrestore(&ctx->wqh.lock, flags); |
135 | |
136 | return events; |
137 | } |
138 | |
139 | static void eventfd_ctx_do_read(struct eventfd_ctx *ctx, __u64 *cnt) |
140 | { |
141 | *cnt = (ctx->flags & EFD_SEMAPHORE) ? 1 : ctx->count; |
142 | ctx->count -= *cnt; |
143 | } |
144 | |
145 | /** |
146 | * eventfd_ctx_remove_wait_queue - Read the current counter and removes wait queue. |
147 | * @ctx: [in] Pointer to eventfd context. |
148 | * @wait: [in] Wait queue to be removed. |
149 | * @cnt: [out] Pointer to the 64-bit counter value. |
150 | * |
151 | * Returns %0 if successful, or the following error codes: |
152 | * |
153 | * -EAGAIN : The operation would have blocked. |
154 | * |
155 | * This is used to atomically remove a wait queue entry from the eventfd wait |
156 | * queue head, and read/reset the counter value. |
157 | */ |
158 | int eventfd_ctx_remove_wait_queue(struct eventfd_ctx *ctx, wait_queue_t *wait, |
159 | __u64 *cnt) |
160 | { |
161 | unsigned long flags; |
162 | |
163 | spin_lock_irqsave(&ctx->wqh.lock, flags); |
164 | eventfd_ctx_do_read(ctx, cnt); |
165 | __remove_wait_queue(&ctx->wqh, wait); |
166 | if (*cnt != 0 && waitqueue_active(&ctx->wqh)) |
167 | wake_up_locked_poll(&ctx->wqh, POLLOUT); |
168 | spin_unlock_irqrestore(&ctx->wqh.lock, flags); |
169 | |
170 | return *cnt != 0 ? 0 : -EAGAIN; |
171 | } |
172 | EXPORT_SYMBOL_GPL(eventfd_ctx_remove_wait_queue); |
173 | |
174 | /** |
175 | * eventfd_ctx_read - Reads the eventfd counter or wait if it is zero. |
176 | * @ctx: [in] Pointer to eventfd context. |
177 | * @no_wait: [in] Different from zero if the operation should not block. |
178 | * @cnt: [out] Pointer to the 64-bit counter value. |
179 | * |
180 | * Returns %0 if successful, or the following error codes: |
181 | * |
182 | * -EAGAIN : The operation would have blocked but @no_wait was non-zero. |
183 | * -ERESTARTSYS : A signal interrupted the wait operation. |
184 | * |
185 | * If @no_wait is zero, the function might sleep until the eventfd internal |
186 | * counter becomes greater than zero. |
187 | */ |
188 | ssize_t eventfd_ctx_read(struct eventfd_ctx *ctx, int no_wait, __u64 *cnt) |
189 | { |
190 | ssize_t res; |
191 | DECLARE_WAITQUEUE(wait, current); |
192 | |
193 | spin_lock_irq(&ctx->wqh.lock); |
194 | *cnt = 0; |
195 | res = -EAGAIN; |
196 | if (ctx->count > 0) |
197 | res = 0; |
198 | else if (!no_wait) { |
199 | __add_wait_queue(&ctx->wqh, &wait); |
200 | for (;;) { |
201 | set_current_state(TASK_INTERRUPTIBLE); |
202 | if (ctx->count > 0) { |
203 | res = 0; |
204 | break; |
205 | } |
206 | if (signal_pending(current)) { |
207 | res = -ERESTARTSYS; |
208 | break; |
209 | } |
210 | spin_unlock_irq(&ctx->wqh.lock); |
211 | schedule(); |
212 | spin_lock_irq(&ctx->wqh.lock); |
213 | } |
214 | __remove_wait_queue(&ctx->wqh, &wait); |
215 | __set_current_state(TASK_RUNNING); |
216 | } |
217 | if (likely(res == 0)) { |
218 | eventfd_ctx_do_read(ctx, cnt); |
219 | if (waitqueue_active(&ctx->wqh)) |
220 | wake_up_locked_poll(&ctx->wqh, POLLOUT); |
221 | } |
222 | spin_unlock_irq(&ctx->wqh.lock); |
223 | |
224 | return res; |
225 | } |
226 | EXPORT_SYMBOL_GPL(eventfd_ctx_read); |
227 | |
228 | static ssize_t eventfd_read(struct file *file, char __user *buf, size_t count, |
229 | loff_t *ppos) |
230 | { |
231 | struct eventfd_ctx *ctx = file->private_data; |
232 | ssize_t res; |
233 | __u64 cnt; |
234 | |
235 | if (count < sizeof(cnt)) |
236 | return -EINVAL; |
237 | res = eventfd_ctx_read(ctx, file->f_flags & O_NONBLOCK, &cnt); |
238 | if (res < 0) |
239 | return res; |
240 | |
241 | return put_user(cnt, (__u64 __user *) buf) ? -EFAULT : sizeof(cnt); |
242 | } |
243 | |
244 | static ssize_t eventfd_write(struct file *file, const char __user *buf, size_t count, |
245 | loff_t *ppos) |
246 | { |
247 | struct eventfd_ctx *ctx = file->private_data; |
248 | ssize_t res; |
249 | __u64 ucnt; |
250 | DECLARE_WAITQUEUE(wait, current); |
251 | |
252 | if (count < sizeof(ucnt)) |
253 | return -EINVAL; |
254 | if (copy_from_user(&ucnt, buf, sizeof(ucnt))) |
255 | return -EFAULT; |
256 | if (ucnt == ULLONG_MAX) |
257 | return -EINVAL; |
258 | spin_lock_irq(&ctx->wqh.lock); |
259 | res = -EAGAIN; |
260 | if (ULLONG_MAX - ctx->count > ucnt) |
261 | res = sizeof(ucnt); |
262 | else if (!(file->f_flags & O_NONBLOCK)) { |
263 | __add_wait_queue(&ctx->wqh, &wait); |
264 | for (res = 0;;) { |
265 | set_current_state(TASK_INTERRUPTIBLE); |
266 | if (ULLONG_MAX - ctx->count > ucnt) { |
267 | res = sizeof(ucnt); |
268 | break; |
269 | } |
270 | if (signal_pending(current)) { |
271 | res = -ERESTARTSYS; |
272 | break; |
273 | } |
274 | spin_unlock_irq(&ctx->wqh.lock); |
275 | schedule(); |
276 | spin_lock_irq(&ctx->wqh.lock); |
277 | } |
278 | __remove_wait_queue(&ctx->wqh, &wait); |
279 | __set_current_state(TASK_RUNNING); |
280 | } |
281 | if (likely(res > 0)) { |
282 | ctx->count += ucnt; |
283 | if (waitqueue_active(&ctx->wqh)) |
284 | wake_up_locked_poll(&ctx->wqh, POLLIN); |
285 | } |
286 | spin_unlock_irq(&ctx->wqh.lock); |
287 | |
288 | return res; |
289 | } |
290 | |
291 | static const struct file_operations eventfd_fops = { |
292 | .release = eventfd_release, |
293 | .poll = eventfd_poll, |
294 | .read = eventfd_read, |
295 | .write = eventfd_write, |
296 | .llseek = noop_llseek, |
297 | }; |
298 | |
299 | /** |
300 | * eventfd_fget - Acquire a reference of an eventfd file descriptor. |
301 | * @fd: [in] Eventfd file descriptor. |
302 | * |
303 | * Returns a pointer to the eventfd file structure in case of success, or the |
304 | * following error pointer: |
305 | * |
306 | * -EBADF : Invalid @fd file descriptor. |
307 | * -EINVAL : The @fd file descriptor is not an eventfd file. |
308 | */ |
309 | struct file *eventfd_fget(int fd) |
310 | { |
311 | struct file *file; |
312 | |
313 | file = fget(fd); |
314 | if (!file) |
315 | return ERR_PTR(-EBADF); |
316 | if (file->f_op != &eventfd_fops) { |
317 | fput(file); |
318 | return ERR_PTR(-EINVAL); |
319 | } |
320 | |
321 | return file; |
322 | } |
323 | EXPORT_SYMBOL_GPL(eventfd_fget); |
324 | |
325 | /** |
326 | * eventfd_ctx_fdget - Acquires a reference to the internal eventfd context. |
327 | * @fd: [in] Eventfd file descriptor. |
328 | * |
329 | * Returns a pointer to the internal eventfd context, otherwise the error |
330 | * pointers returned by the following functions: |
331 | * |
332 | * eventfd_fget |
333 | */ |
334 | struct eventfd_ctx *eventfd_ctx_fdget(int fd) |
335 | { |
336 | struct file *file; |
337 | struct eventfd_ctx *ctx; |
338 | |
339 | file = eventfd_fget(fd); |
340 | if (IS_ERR(file)) |
341 | return (struct eventfd_ctx *) file; |
342 | ctx = eventfd_ctx_get(file->private_data); |
343 | fput(file); |
344 | |
345 | return ctx; |
346 | } |
347 | EXPORT_SYMBOL_GPL(eventfd_ctx_fdget); |
348 | |
349 | /** |
350 | * eventfd_ctx_fileget - Acquires a reference to the internal eventfd context. |
351 | * @file: [in] Eventfd file pointer. |
352 | * |
353 | * Returns a pointer to the internal eventfd context, otherwise the error |
354 | * pointer: |
355 | * |
356 | * -EINVAL : The @fd file descriptor is not an eventfd file. |
357 | */ |
358 | struct eventfd_ctx *eventfd_ctx_fileget(struct file *file) |
359 | { |
360 | if (file->f_op != &eventfd_fops) |
361 | return ERR_PTR(-EINVAL); |
362 | |
363 | return eventfd_ctx_get(file->private_data); |
364 | } |
365 | EXPORT_SYMBOL_GPL(eventfd_ctx_fileget); |
366 | |
367 | /** |
368 | * eventfd_file_create - Creates an eventfd file pointer. |
369 | * @count: Initial eventfd counter value. |
370 | * @flags: Flags for the eventfd file. |
371 | * |
372 | * This function creates an eventfd file pointer, w/out installing it into |
373 | * the fd table. This is useful when the eventfd file is used during the |
374 | * initialization of data structures that require extra setup after the eventfd |
375 | * creation. So the eventfd creation is split into the file pointer creation |
376 | * phase, and the file descriptor installation phase. |
377 | * In this way races with userspace closing the newly installed file descriptor |
378 | * can be avoided. |
379 | * Returns an eventfd file pointer, or a proper error pointer. |
380 | */ |
381 | struct file *eventfd_file_create(unsigned int count, int flags) |
382 | { |
383 | struct file *file; |
384 | struct eventfd_ctx *ctx; |
385 | |
386 | /* Check the EFD_* constants for consistency. */ |
387 | BUILD_BUG_ON(EFD_CLOEXEC != O_CLOEXEC); |
388 | BUILD_BUG_ON(EFD_NONBLOCK != O_NONBLOCK); |
389 | |
390 | if (flags & ~EFD_FLAGS_SET) |
391 | return ERR_PTR(-EINVAL); |
392 | |
393 | ctx = kmalloc(sizeof(*ctx), GFP_KERNEL); |
394 | if (!ctx) |
395 | return ERR_PTR(-ENOMEM); |
396 | |
397 | kref_init(&ctx->kref); |
398 | init_waitqueue_head(&ctx->wqh); |
399 | ctx->count = count; |
400 | ctx->flags = flags; |
401 | |
402 | file = anon_inode_getfile("[eventfd]", &eventfd_fops, ctx, |
403 | O_RDWR | (flags & EFD_SHARED_FCNTL_FLAGS)); |
404 | if (IS_ERR(file)) |
405 | eventfd_free_ctx(ctx); |
406 | |
407 | return file; |
408 | } |
409 | |
410 | SYSCALL_DEFINE2(eventfd2, unsigned int, count, int, flags) |
411 | { |
412 | int fd, error; |
413 | struct file *file; |
414 | |
415 | error = get_unused_fd_flags(flags & EFD_SHARED_FCNTL_FLAGS); |
416 | if (error < 0) |
417 | return error; |
418 | fd = error; |
419 | |
420 | file = eventfd_file_create(count, flags); |
421 | if (IS_ERR(file)) { |
422 | error = PTR_ERR(file); |
423 | goto err_put_unused_fd; |
424 | } |
425 | fd_install(fd, file); |
426 | |
427 | return fd; |
428 | |
429 | err_put_unused_fd: |
430 | put_unused_fd(fd); |
431 | |
432 | return error; |
433 | } |
434 | |
435 | SYSCALL_DEFINE1(eventfd, unsigned int, count) |
436 | { |
437 | return sys_eventfd2(count, 0); |
438 | } |
439 | |
440 |
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