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Merge branch 'drm-fixes' of git://people.freedesktop.org/~airlied/linux
[mirror_ubuntu-zesty-kernel.git] / fs / eventfd.c
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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>
5a0e3ad6 14#include <linux/slab.h>
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15#include <linux/list.h>
16#include <linux/spinlock.h>
17#include <linux/anon_inodes.h>
7747cdb2 18#include <linux/syscalls.h>
630d9c47 19#include <linux/export.h>
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20#include <linux/kref.h>
21#include <linux/eventfd.h>
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22#include <linux/proc_fs.h>
23#include <linux/seq_file.h>
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24
25struct eventfd_ctx {
13389010 26 struct kref kref;
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27 wait_queue_head_t wqh;
28 /*
29 * Every time that a write(2) is performed on an eventfd, the
30 * value of the __u64 being written is added to "count" and a
31 * wakeup is performed on "wqh". A read(2) will return the "count"
32 * value to userspace, and will reset "count" to zero. The kernel
13389010 33 * side eventfd_signal() also, adds to the "count" counter and
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34 * issue a wakeup.
35 */
36 __u64 count;
bcd0b235 37 unsigned int flags;
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38};
39
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40/**
41 * eventfd_signal - Adds @n to the eventfd counter.
42 * @ctx: [in] Pointer to the eventfd context.
43 * @n: [in] Value of the counter to be added to the eventfd internal counter.
44 * The value cannot be negative.
45 *
46 * This function is supposed to be called by the kernel in paths that do not
47 * allow sleeping. In this function we allow the counter to reach the ULLONG_MAX
48 * value, and we signal this as overflow condition by returining a POLLERR
49 * to poll(2).
50 *
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51 * Returns the amount by which the counter was incrememnted. This will be less
52 * than @n if the counter has overflowed.
e1ad7468 53 */
ee62c6b2 54__u64 eventfd_signal(struct eventfd_ctx *ctx, __u64 n)
e1ad7468 55{
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56 unsigned long flags;
57
d48eb233 58 spin_lock_irqsave(&ctx->wqh.lock, flags);
e1ad7468 59 if (ULLONG_MAX - ctx->count < n)
ee62c6b2 60 n = ULLONG_MAX - ctx->count;
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61 ctx->count += n;
62 if (waitqueue_active(&ctx->wqh))
39510888 63 wake_up_locked_poll(&ctx->wqh, POLLIN);
d48eb233 64 spin_unlock_irqrestore(&ctx->wqh.lock, flags);
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65
66 return n;
67}
5718607b 68EXPORT_SYMBOL_GPL(eventfd_signal);
e1ad7468 69
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70static void eventfd_free_ctx(struct eventfd_ctx *ctx)
71{
72 kfree(ctx);
73}
74
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75static void eventfd_free(struct kref *kref)
76{
77 struct eventfd_ctx *ctx = container_of(kref, struct eventfd_ctx, kref);
78
562787a5 79 eventfd_free_ctx(ctx);
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80}
81
82/**
83 * eventfd_ctx_get - Acquires a reference to the internal eventfd context.
84 * @ctx: [in] Pointer to the eventfd context.
85 *
86 * Returns: In case of success, returns a pointer to the eventfd context.
87 */
88struct eventfd_ctx *eventfd_ctx_get(struct eventfd_ctx *ctx)
89{
90 kref_get(&ctx->kref);
91 return ctx;
92}
93EXPORT_SYMBOL_GPL(eventfd_ctx_get);
94
95/**
96 * eventfd_ctx_put - Releases a reference to the internal eventfd context.
97 * @ctx: [in] Pointer to eventfd context.
98 *
99 * The eventfd context reference must have been previously acquired either
36182185 100 * with eventfd_ctx_get() or eventfd_ctx_fdget().
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101 */
102void eventfd_ctx_put(struct eventfd_ctx *ctx)
103{
104 kref_put(&ctx->kref, eventfd_free);
105}
106EXPORT_SYMBOL_GPL(eventfd_ctx_put);
107
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108static int eventfd_release(struct inode *inode, struct file *file)
109{
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110 struct eventfd_ctx *ctx = file->private_data;
111
112 wake_up_poll(&ctx->wqh, POLLHUP);
113 eventfd_ctx_put(ctx);
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114 return 0;
115}
116
117static unsigned int eventfd_poll(struct file *file, poll_table *wait)
118{
119 struct eventfd_ctx *ctx = file->private_data;
120 unsigned int events = 0;
e22553e2 121 u64 count;
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122
123 poll_wait(file, &ctx->wqh, wait);
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124 smp_rmb();
125 count = ctx->count;
e1ad7468 126
e22553e2 127 if (count > 0)
e1ad7468 128 events |= POLLIN;
e22553e2 129 if (count == ULLONG_MAX)
e1ad7468 130 events |= POLLERR;
e22553e2 131 if (ULLONG_MAX - 1 > count)
e1ad7468 132 events |= POLLOUT;
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133
134 return events;
135}
136
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137static void eventfd_ctx_do_read(struct eventfd_ctx *ctx, __u64 *cnt)
138{
139 *cnt = (ctx->flags & EFD_SEMAPHORE) ? 1 : ctx->count;
140 ctx->count -= *cnt;
141}
142
143/**
144 * eventfd_ctx_remove_wait_queue - Read the current counter and removes wait queue.
145 * @ctx: [in] Pointer to eventfd context.
146 * @wait: [in] Wait queue to be removed.
36182185 147 * @cnt: [out] Pointer to the 64-bit counter value.
cb289d62 148 *
36182185 149 * Returns %0 if successful, or the following error codes:
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150 *
151 * -EAGAIN : The operation would have blocked.
152 *
153 * This is used to atomically remove a wait queue entry from the eventfd wait
154 * queue head, and read/reset the counter value.
155 */
156int eventfd_ctx_remove_wait_queue(struct eventfd_ctx *ctx, wait_queue_t *wait,
157 __u64 *cnt)
158{
159 unsigned long flags;
160
161 spin_lock_irqsave(&ctx->wqh.lock, flags);
162 eventfd_ctx_do_read(ctx, cnt);
163 __remove_wait_queue(&ctx->wqh, wait);
164 if (*cnt != 0 && waitqueue_active(&ctx->wqh))
165 wake_up_locked_poll(&ctx->wqh, POLLOUT);
166 spin_unlock_irqrestore(&ctx->wqh.lock, flags);
167
168 return *cnt != 0 ? 0 : -EAGAIN;
169}
170EXPORT_SYMBOL_GPL(eventfd_ctx_remove_wait_queue);
171
172/**
173 * eventfd_ctx_read - Reads the eventfd counter or wait if it is zero.
174 * @ctx: [in] Pointer to eventfd context.
175 * @no_wait: [in] Different from zero if the operation should not block.
36182185 176 * @cnt: [out] Pointer to the 64-bit counter value.
cb289d62 177 *
36182185 178 * Returns %0 if successful, or the following error codes:
cb289d62 179 *
36182185 180 * -EAGAIN : The operation would have blocked but @no_wait was non-zero.
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181 * -ERESTARTSYS : A signal interrupted the wait operation.
182 *
183 * If @no_wait is zero, the function might sleep until the eventfd internal
184 * counter becomes greater than zero.
185 */
186ssize_t eventfd_ctx_read(struct eventfd_ctx *ctx, int no_wait, __u64 *cnt)
e1ad7468 187{
e1ad7468 188 ssize_t res;
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189 DECLARE_WAITQUEUE(wait, current);
190
d48eb233 191 spin_lock_irq(&ctx->wqh.lock);
cb289d62 192 *cnt = 0;
e1ad7468 193 res = -EAGAIN;
bcd0b235 194 if (ctx->count > 0)
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195 res = 0;
196 else if (!no_wait) {
e1ad7468 197 __add_wait_queue(&ctx->wqh, &wait);
cb289d62 198 for (;;) {
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199 set_current_state(TASK_INTERRUPTIBLE);
200 if (ctx->count > 0) {
cb289d62 201 res = 0;
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202 break;
203 }
204 if (signal_pending(current)) {
205 res = -ERESTARTSYS;
206 break;
207 }
d48eb233 208 spin_unlock_irq(&ctx->wqh.lock);
e1ad7468 209 schedule();
d48eb233 210 spin_lock_irq(&ctx->wqh.lock);
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211 }
212 __remove_wait_queue(&ctx->wqh, &wait);
213 __set_current_state(TASK_RUNNING);
214 }
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215 if (likely(res == 0)) {
216 eventfd_ctx_do_read(ctx, cnt);
e1ad7468 217 if (waitqueue_active(&ctx->wqh))
39510888 218 wake_up_locked_poll(&ctx->wqh, POLLOUT);
e1ad7468 219 }
d48eb233 220 spin_unlock_irq(&ctx->wqh.lock);
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221
222 return res;
223}
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224EXPORT_SYMBOL_GPL(eventfd_ctx_read);
225
226static ssize_t eventfd_read(struct file *file, char __user *buf, size_t count,
227 loff_t *ppos)
228{
229 struct eventfd_ctx *ctx = file->private_data;
230 ssize_t res;
231 __u64 cnt;
232
233 if (count < sizeof(cnt))
234 return -EINVAL;
235 res = eventfd_ctx_read(ctx, file->f_flags & O_NONBLOCK, &cnt);
236 if (res < 0)
237 return res;
238
239 return put_user(cnt, (__u64 __user *) buf) ? -EFAULT : sizeof(cnt);
240}
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241
242static ssize_t eventfd_write(struct file *file, const char __user *buf, size_t count,
243 loff_t *ppos)
244{
245 struct eventfd_ctx *ctx = file->private_data;
246 ssize_t res;
247 __u64 ucnt;
248 DECLARE_WAITQUEUE(wait, current);
249
250 if (count < sizeof(ucnt))
251 return -EINVAL;
252 if (copy_from_user(&ucnt, buf, sizeof(ucnt)))
253 return -EFAULT;
254 if (ucnt == ULLONG_MAX)
255 return -EINVAL;
d48eb233 256 spin_lock_irq(&ctx->wqh.lock);
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257 res = -EAGAIN;
258 if (ULLONG_MAX - ctx->count > ucnt)
259 res = sizeof(ucnt);
260 else if (!(file->f_flags & O_NONBLOCK)) {
261 __add_wait_queue(&ctx->wqh, &wait);
262 for (res = 0;;) {
263 set_current_state(TASK_INTERRUPTIBLE);
264 if (ULLONG_MAX - ctx->count > ucnt) {
265 res = sizeof(ucnt);
266 break;
267 }
268 if (signal_pending(current)) {
269 res = -ERESTARTSYS;
270 break;
271 }
d48eb233 272 spin_unlock_irq(&ctx->wqh.lock);
e1ad7468 273 schedule();
d48eb233 274 spin_lock_irq(&ctx->wqh.lock);
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275 }
276 __remove_wait_queue(&ctx->wqh, &wait);
277 __set_current_state(TASK_RUNNING);
278 }
bcd0b235 279 if (likely(res > 0)) {
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280 ctx->count += ucnt;
281 if (waitqueue_active(&ctx->wqh))
39510888 282 wake_up_locked_poll(&ctx->wqh, POLLIN);
e1ad7468 283 }
d48eb233 284 spin_unlock_irq(&ctx->wqh.lock);
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285
286 return res;
287}
288
cbac5542 289#ifdef CONFIG_PROC_FS
a3816ab0 290static void eventfd_show_fdinfo(struct seq_file *m, struct file *f)
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291{
292 struct eventfd_ctx *ctx = f->private_data;
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293
294 spin_lock_irq(&ctx->wqh.lock);
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295 seq_printf(m, "eventfd-count: %16llx\n",
296 (unsigned long long)ctx->count);
cbac5542 297 spin_unlock_irq(&ctx->wqh.lock);
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298}
299#endif
300
e1ad7468 301static const struct file_operations eventfd_fops = {
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302#ifdef CONFIG_PROC_FS
303 .show_fdinfo = eventfd_show_fdinfo,
304#endif
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305 .release = eventfd_release,
306 .poll = eventfd_poll,
307 .read = eventfd_read,
308 .write = eventfd_write,
6038f373 309 .llseek = noop_llseek,
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310};
311
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312/**
313 * eventfd_fget - Acquire a reference of an eventfd file descriptor.
314 * @fd: [in] Eventfd file descriptor.
315 *
316 * Returns a pointer to the eventfd file structure in case of success, or the
317 * following error pointer:
318 *
319 * -EBADF : Invalid @fd file descriptor.
320 * -EINVAL : The @fd file descriptor is not an eventfd file.
321 */
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322struct file *eventfd_fget(int fd)
323{
324 struct file *file;
325
326 file = fget(fd);
327 if (!file)
328 return ERR_PTR(-EBADF);
329 if (file->f_op != &eventfd_fops) {
330 fput(file);
331 return ERR_PTR(-EINVAL);
332 }
333
334 return file;
335}
5718607b 336EXPORT_SYMBOL_GPL(eventfd_fget);
e1ad7468 337
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338/**
339 * eventfd_ctx_fdget - Acquires a reference to the internal eventfd context.
340 * @fd: [in] Eventfd file descriptor.
341 *
342 * Returns a pointer to the internal eventfd context, otherwise the error
343 * pointers returned by the following functions:
344 *
345 * eventfd_fget
346 */
347struct eventfd_ctx *eventfd_ctx_fdget(int fd)
348{
13389010 349 struct eventfd_ctx *ctx;
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350 struct fd f = fdget(fd);
351 if (!f.file)
352 return ERR_PTR(-EBADF);
353 ctx = eventfd_ctx_fileget(f.file);
354 fdput(f);
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355 return ctx;
356}
357EXPORT_SYMBOL_GPL(eventfd_ctx_fdget);
358
359/**
360 * eventfd_ctx_fileget - Acquires a reference to the internal eventfd context.
361 * @file: [in] Eventfd file pointer.
362 *
363 * Returns a pointer to the internal eventfd context, otherwise the error
364 * pointer:
365 *
366 * -EINVAL : The @fd file descriptor is not an eventfd file.
367 */
368struct eventfd_ctx *eventfd_ctx_fileget(struct file *file)
369{
370 if (file->f_op != &eventfd_fops)
371 return ERR_PTR(-EINVAL);
372
373 return eventfd_ctx_get(file->private_data);
374}
375EXPORT_SYMBOL_GPL(eventfd_ctx_fileget);
376
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377/**
378 * eventfd_file_create - Creates an eventfd file pointer.
379 * @count: Initial eventfd counter value.
380 * @flags: Flags for the eventfd file.
381 *
382 * This function creates an eventfd file pointer, w/out installing it into
383 * the fd table. This is useful when the eventfd file is used during the
384 * initialization of data structures that require extra setup after the eventfd
385 * creation. So the eventfd creation is split into the file pointer creation
386 * phase, and the file descriptor installation phase.
387 * In this way races with userspace closing the newly installed file descriptor
388 * can be avoided.
389 * Returns an eventfd file pointer, or a proper error pointer.
390 */
391struct file *eventfd_file_create(unsigned int count, int flags)
e1ad7468 392{
562787a5 393 struct file *file;
e1ad7468 394 struct eventfd_ctx *ctx;
e1ad7468 395
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396 /* Check the EFD_* constants for consistency. */
397 BUILD_BUG_ON(EFD_CLOEXEC != O_CLOEXEC);
398 BUILD_BUG_ON(EFD_NONBLOCK != O_NONBLOCK);
399
bcd0b235 400 if (flags & ~EFD_FLAGS_SET)
562787a5 401 return ERR_PTR(-EINVAL);
b087498e 402
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403 ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
404 if (!ctx)
562787a5 405 return ERR_PTR(-ENOMEM);
e1ad7468 406
13389010 407 kref_init(&ctx->kref);
e1ad7468 408 init_waitqueue_head(&ctx->wqh);
e1ad7468 409 ctx->count = count;
bcd0b235 410 ctx->flags = flags;
e1ad7468 411
562787a5 412 file = anon_inode_getfile("[eventfd]", &eventfd_fops, ctx,
628ff7c1 413 O_RDWR | (flags & EFD_SHARED_FCNTL_FLAGS));
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414 if (IS_ERR(file))
415 eventfd_free_ctx(ctx);
416
417 return file;
418}
419
420SYSCALL_DEFINE2(eventfd2, unsigned int, count, int, flags)
421{
422 int fd, error;
423 struct file *file;
424
425 error = get_unused_fd_flags(flags & EFD_SHARED_FCNTL_FLAGS);
426 if (error < 0)
427 return error;
428 fd = error;
429
430 file = eventfd_file_create(count, flags);
431 if (IS_ERR(file)) {
432 error = PTR_ERR(file);
433 goto err_put_unused_fd;
434 }
435 fd_install(fd, file);
436
2030a42c 437 return fd;
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438
439err_put_unused_fd:
440 put_unused_fd(fd);
441
442 return error;
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443}
444
d4e82042 445SYSCALL_DEFINE1(eventfd, unsigned int, count)
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446{
447 return sys_eventfd2(count, 0);
448}
bcd0b235 449