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>
17 #include <linux/syscalls.h>
18 #include <linux/module.h>
19 #include <linux/kref.h>
20 #include <linux/eventfd.h>
21
22 struct eventfd_ctx {
23 struct kref kref;
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
30 * side eventfd_signal() also, adds to the "count" counter and
31 * issue a wakeup.
32 */
33 __u64 count;
34 unsigned int flags;
35 };
36
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.
52 */
53 int eventfd_signal(struct eventfd_ctx *ctx, int n)
54 {
55 unsigned long flags;
56
57 if (n < 0)
58 return -EINVAL;
59 spin_lock_irqsave(&ctx->wqh.lock, flags);
60 if (ULLONG_MAX - ctx->count < n)
61 n = (int) (ULLONG_MAX - ctx->count);
62 ctx->count += n;
63 if (waitqueue_active(&ctx->wqh))
64 wake_up_locked_poll(&ctx->wqh, POLLIN);
65 spin_unlock_irqrestore(&ctx->wqh.lock, flags);
66
67 return n;
68 }
69 EXPORT_SYMBOL_GPL(eventfd_signal);
70
71 static void eventfd_free(struct kref *kref)
72 {
73 struct eventfd_ctx *ctx = container_of(kref, struct eventfd_ctx, kref);
74
75 kfree(ctx);
76 }
77
78 /**
79 * eventfd_ctx_get - Acquires a reference to the internal eventfd context.
80 * @ctx: [in] Pointer to the eventfd context.
81 *
82 * Returns: In case of success, returns a pointer to the eventfd context.
83 */
84 struct eventfd_ctx *eventfd_ctx_get(struct eventfd_ctx *ctx)
85 {
86 kref_get(&ctx->kref);
87 return ctx;
88 }
89 EXPORT_SYMBOL_GPL(eventfd_ctx_get);
90
91 /**
92 * eventfd_ctx_put - Releases a reference to the internal eventfd context.
93 * @ctx: [in] Pointer to eventfd context.
94 *
95 * The eventfd context reference must have been previously acquired either
96 * with eventfd_ctx_get() or eventfd_ctx_fdget()).
97 */
98 void eventfd_ctx_put(struct eventfd_ctx *ctx)
99 {
100 kref_put(&ctx->kref, eventfd_free);
101 }
102 EXPORT_SYMBOL_GPL(eventfd_ctx_put);
103
104 static int eventfd_release(struct inode *inode, struct file *file)
105 {
106 struct eventfd_ctx *ctx = file->private_data;
107
108 wake_up_poll(&ctx->wqh, POLLHUP);
109 eventfd_ctx_put(ctx);
110 return 0;
111 }
112
113 static unsigned int eventfd_poll(struct file *file, poll_table *wait)
114 {
115 struct eventfd_ctx *ctx = file->private_data;
116 unsigned int events = 0;
117 unsigned long flags;
118
119 poll_wait(file, &ctx->wqh, wait);
120
121 spin_lock_irqsave(&ctx->wqh.lock, flags);
122 if (ctx->count > 0)
123 events |= POLLIN;
124 if (ctx->count == ULLONG_MAX)
125 events |= POLLERR;
126 if (ULLONG_MAX - 1 > ctx->count)
127 events |= POLLOUT;
128 spin_unlock_irqrestore(&ctx->wqh.lock, flags);
129
130 return events;
131 }
132
133 static ssize_t eventfd_read(struct file *file, char __user *buf, size_t count,
134 loff_t *ppos)
135 {
136 struct eventfd_ctx *ctx = file->private_data;
137 ssize_t res;
138 __u64 ucnt = 0;
139 DECLARE_WAITQUEUE(wait, current);
140
141 if (count < sizeof(ucnt))
142 return -EINVAL;
143 spin_lock_irq(&ctx->wqh.lock);
144 res = -EAGAIN;
145 if (ctx->count > 0)
146 res = sizeof(ucnt);
147 else if (!(file->f_flags & O_NONBLOCK)) {
148 __add_wait_queue(&ctx->wqh, &wait);
149 for (res = 0;;) {
150 set_current_state(TASK_INTERRUPTIBLE);
151 if (ctx->count > 0) {
152 res = sizeof(ucnt);
153 break;
154 }
155 if (signal_pending(current)) {
156 res = -ERESTARTSYS;
157 break;
158 }
159 spin_unlock_irq(&ctx->wqh.lock);
160 schedule();
161 spin_lock_irq(&ctx->wqh.lock);
162 }
163 __remove_wait_queue(&ctx->wqh, &wait);
164 __set_current_state(TASK_RUNNING);
165 }
166 if (likely(res > 0)) {
167 ucnt = (ctx->flags & EFD_SEMAPHORE) ? 1 : ctx->count;
168 ctx->count -= ucnt;
169 if (waitqueue_active(&ctx->wqh))
170 wake_up_locked_poll(&ctx->wqh, POLLOUT);
171 }
172 spin_unlock_irq(&ctx->wqh.lock);
173 if (res > 0 && put_user(ucnt, (__u64 __user *) buf))
174 return -EFAULT;
175
176 return res;
177 }
178
179 static ssize_t eventfd_write(struct file *file, const char __user *buf, size_t count,
180 loff_t *ppos)
181 {
182 struct eventfd_ctx *ctx = file->private_data;
183 ssize_t res;
184 __u64 ucnt;
185 DECLARE_WAITQUEUE(wait, current);
186
187 if (count < sizeof(ucnt))
188 return -EINVAL;
189 if (copy_from_user(&ucnt, buf, sizeof(ucnt)))
190 return -EFAULT;
191 if (ucnt == ULLONG_MAX)
192 return -EINVAL;
193 spin_lock_irq(&ctx->wqh.lock);
194 res = -EAGAIN;
195 if (ULLONG_MAX - ctx->count > ucnt)
196 res = sizeof(ucnt);
197 else if (!(file->f_flags & O_NONBLOCK)) {
198 __add_wait_queue(&ctx->wqh, &wait);
199 for (res = 0;;) {
200 set_current_state(TASK_INTERRUPTIBLE);
201 if (ULLONG_MAX - ctx->count > ucnt) {
202 res = sizeof(ucnt);
203 break;
204 }
205 if (signal_pending(current)) {
206 res = -ERESTARTSYS;
207 break;
208 }
209 spin_unlock_irq(&ctx->wqh.lock);
210 schedule();
211 spin_lock_irq(&ctx->wqh.lock);
212 }
213 __remove_wait_queue(&ctx->wqh, &wait);
214 __set_current_state(TASK_RUNNING);
215 }
216 if (likely(res > 0)) {
217 ctx->count += ucnt;
218 if (waitqueue_active(&ctx->wqh))
219 wake_up_locked_poll(&ctx->wqh, POLLIN);
220 }
221 spin_unlock_irq(&ctx->wqh.lock);
222
223 return res;
224 }
225
226 static const struct file_operations eventfd_fops = {
227 .release = eventfd_release,
228 .poll = eventfd_poll,
229 .read = eventfd_read,
230 .write = eventfd_write,
231 };
232
233 /**
234 * eventfd_fget - Acquire a reference of an eventfd file descriptor.
235 * @fd: [in] Eventfd file descriptor.
236 *
237 * Returns a pointer to the eventfd file structure in case of success, or the
238 * following error pointer:
239 *
240 * -EBADF : Invalid @fd file descriptor.
241 * -EINVAL : The @fd file descriptor is not an eventfd file.
242 */
243 struct file *eventfd_fget(int fd)
244 {
245 struct file *file;
246
247 file = fget(fd);
248 if (!file)
249 return ERR_PTR(-EBADF);
250 if (file->f_op != &eventfd_fops) {
251 fput(file);
252 return ERR_PTR(-EINVAL);
253 }
254
255 return file;
256 }
257 EXPORT_SYMBOL_GPL(eventfd_fget);
258
259 /**
260 * eventfd_ctx_fdget - Acquires a reference to the internal eventfd context.
261 * @fd: [in] Eventfd file descriptor.
262 *
263 * Returns a pointer to the internal eventfd context, otherwise the error
264 * pointers returned by the following functions:
265 *
266 * eventfd_fget
267 */
268 struct eventfd_ctx *eventfd_ctx_fdget(int fd)
269 {
270 struct file *file;
271 struct eventfd_ctx *ctx;
272
273 file = eventfd_fget(fd);
274 if (IS_ERR(file))
275 return (struct eventfd_ctx *) file;
276 ctx = eventfd_ctx_get(file->private_data);
277 fput(file);
278
279 return ctx;
280 }
281 EXPORT_SYMBOL_GPL(eventfd_ctx_fdget);
282
283 /**
284 * eventfd_ctx_fileget - Acquires a reference to the internal eventfd context.
285 * @file: [in] Eventfd file pointer.
286 *
287 * Returns a pointer to the internal eventfd context, otherwise the error
288 * pointer:
289 *
290 * -EINVAL : The @fd file descriptor is not an eventfd file.
291 */
292 struct eventfd_ctx *eventfd_ctx_fileget(struct file *file)
293 {
294 if (file->f_op != &eventfd_fops)
295 return ERR_PTR(-EINVAL);
296
297 return eventfd_ctx_get(file->private_data);
298 }
299 EXPORT_SYMBOL_GPL(eventfd_ctx_fileget);
300
301 SYSCALL_DEFINE2(eventfd2, unsigned int, count, int, flags)
302 {
303 int fd;
304 struct eventfd_ctx *ctx;
305
306 /* Check the EFD_* constants for consistency. */
307 BUILD_BUG_ON(EFD_CLOEXEC != O_CLOEXEC);
308 BUILD_BUG_ON(EFD_NONBLOCK != O_NONBLOCK);
309
310 if (flags & ~EFD_FLAGS_SET)
311 return -EINVAL;
312
313 ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
314 if (!ctx)
315 return -ENOMEM;
316
317 kref_init(&ctx->kref);
318 init_waitqueue_head(&ctx->wqh);
319 ctx->count = count;
320 ctx->flags = flags;
321
322 /*
323 * When we call this, the initialization must be complete, since
324 * anon_inode_getfd() will install the fd.
325 */
326 fd = anon_inode_getfd("[eventfd]", &eventfd_fops, ctx,
327 flags & EFD_SHARED_FCNTL_FLAGS);
328 if (fd < 0)
329 kfree(ctx);
330 return fd;
331 }
332
333 SYSCALL_DEFINE1(eventfd, unsigned int, count)
334 {
335 return sys_eventfd2(count, 0);
336 }
337
338
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