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