1 /*
2 * userio kernel serio device emulation module
3 * Copyright (C) 2015 Red Hat
4 * Copyright (C) 2015 Stephen Chandler Paul <thatslyude@gmail.com>
5 *
6 * This program is free software; you can redistribute it and/or modify it
7 * under the terms of the GNU Lesser General Public License as published by
8 * the Free Software Foundation; either version 2 of the License, or (at
9 * your option) any later version.
10 *
11 * This program is distributed in the hope that it will be useful, but
12 * WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser
14 * General Public License for more details.
15 */
16
17 #include <linux/circ_buf.h>
18 #include <linux/mutex.h>
19 #include <linux/module.h>
20 #include <linux/init.h>
21 #include <linux/kernel.h>
22 #include <linux/serio.h>
23 #include <linux/slab.h>
24 #include <linux/fs.h>
25 #include <linux/miscdevice.h>
26 #include <linux/sched.h>
27 #include <linux/poll.h>
28 #include <uapi/linux/userio.h>
29
30 #define USERIO_NAME "userio"
31 #define USERIO_BUFSIZE 16
32
33 static struct miscdevice userio_misc;
34
35 struct userio_device {
36 struct serio *serio;
37 struct mutex mutex;
38
39 bool running;
40
41 u8 head;
42 u8 tail;
43
44 spinlock_t buf_lock;
45 unsigned char buf[USERIO_BUFSIZE];
46
47 wait_queue_head_t waitq;
48 };
49
50 /**
51 * userio_device_write - Write data from serio to a userio device in userspace
52 * @id: The serio port for the userio device
53 * @val: The data to write to the device
54 */
userio_device_write(struct serio * id,unsigned char val)55 static int userio_device_write(struct serio *id, unsigned char val)
56 {
57 struct userio_device *userio = id->port_data;
58 unsigned long flags;
59
60 spin_lock_irqsave(&userio->buf_lock, flags);
61
62 userio->buf[userio->head] = val;
63 userio->head = (userio->head + 1) % USERIO_BUFSIZE;
64
65 if (userio->head == userio->tail)
66 dev_warn(userio_misc.this_device,
67 "Buffer overflowed, userio client isn't keeping up");
68
69 spin_unlock_irqrestore(&userio->buf_lock, flags);
70
71 wake_up_interruptible(&userio->waitq);
72
73 return 0;
74 }
75
userio_char_open(struct inode * inode,struct file * file)76 static int userio_char_open(struct inode *inode, struct file *file)
77 {
78 struct userio_device *userio;
79
80 userio = kzalloc(sizeof(struct userio_device), GFP_KERNEL);
81 if (!userio)
82 return -ENOMEM;
83
84 mutex_init(&userio->mutex);
85 spin_lock_init(&userio->buf_lock);
86 init_waitqueue_head(&userio->waitq);
87
88 userio->serio = kzalloc(sizeof(struct serio), GFP_KERNEL);
89 if (!userio->serio) {
90 kfree(userio);
91 return -ENOMEM;
92 }
93
94 userio->serio->write = userio_device_write;
95 userio->serio->port_data = userio;
96
97 file->private_data = userio;
98
99 return 0;
100 }
101
userio_char_release(struct inode * inode,struct file * file)102 static int userio_char_release(struct inode *inode, struct file *file)
103 {
104 struct userio_device *userio = file->private_data;
105
106 if (userio->running) {
107 /*
108 * Don't free the serio port here, serio_unregister_port()
109 * does it for us.
110 */
111 serio_unregister_port(userio->serio);
112 } else {
113 kfree(userio->serio);
114 }
115
116 kfree(userio);
117
118 return 0;
119 }
120
userio_char_read(struct file * file,char __user * user_buffer,size_t count,loff_t * ppos)121 static ssize_t userio_char_read(struct file *file, char __user *user_buffer,
122 size_t count, loff_t *ppos)
123 {
124 struct userio_device *userio = file->private_data;
125 int error;
126 size_t nonwrap_len, copylen;
127 unsigned char buf[USERIO_BUFSIZE];
128 unsigned long flags;
129
130 /*
131 * By the time we get here, the data that was waiting might have
132 * been taken by another thread. Grab the buffer lock and check if
133 * there's still any data waiting, otherwise repeat this process
134 * until we have data (unless the file descriptor is non-blocking
135 * of course).
136 */
137 for (;;) {
138 spin_lock_irqsave(&userio->buf_lock, flags);
139
140 nonwrap_len = CIRC_CNT_TO_END(userio->head,
141 userio->tail,
142 USERIO_BUFSIZE);
143 copylen = min(nonwrap_len, count);
144 if (copylen) {
145 memcpy(buf, &userio->buf[userio->tail], copylen);
146 userio->tail = (userio->tail + copylen) %
147 USERIO_BUFSIZE;
148 }
149
150 spin_unlock_irqrestore(&userio->buf_lock, flags);
151
152 if (nonwrap_len)
153 break;
154
155 /* buffer was/is empty */
156 if (file->f_flags & O_NONBLOCK)
157 return -EAGAIN;
158
159 /*
160 * count == 0 is special - no IO is done but we check
161 * for error conditions (see above).
162 */
163 if (count == 0)
164 return 0;
165
166 error = wait_event_interruptible(userio->waitq,
167 userio->head != userio->tail);
168 if (error)
169 return error;
170 }
171
172 if (copylen)
173 if (copy_to_user(user_buffer, buf, copylen))
174 return -EFAULT;
175
176 return copylen;
177 }
178
userio_char_write(struct file * file,const char __user * buffer,size_t count,loff_t * ppos)179 static ssize_t userio_char_write(struct file *file, const char __user *buffer,
180 size_t count, loff_t *ppos)
181 {
182 struct userio_device *userio = file->private_data;
183 struct userio_cmd cmd;
184 int error;
185
186 if (count != sizeof(cmd)) {
187 dev_warn(userio_misc.this_device, "Invalid payload size\n");
188 return -EINVAL;
189 }
190
191 if (copy_from_user(&cmd, buffer, sizeof(cmd)))
192 return -EFAULT;
193
194 error = mutex_lock_interruptible(&userio->mutex);
195 if (error)
196 return error;
197
198 switch (cmd.type) {
199 case USERIO_CMD_REGISTER:
200 if (!userio->serio->id.type) {
201 dev_warn(userio_misc.this_device,
202 "No port type given on /dev/userio\n");
203
204 error = -EINVAL;
205 goto out;
206 }
207
208 if (userio->running) {
209 dev_warn(userio_misc.this_device,
210 "Begin command sent, but we're already running\n");
211 error = -EBUSY;
212 goto out;
213 }
214
215 userio->running = true;
216 serio_register_port(userio->serio);
217 break;
218
219 case USERIO_CMD_SET_PORT_TYPE:
220 if (userio->running) {
221 dev_warn(userio_misc.this_device,
222 "Can't change port type on an already running userio instance\n");
223 error = -EBUSY;
224 goto out;
225 }
226
227 userio->serio->id.type = cmd.data;
228 break;
229
230 case USERIO_CMD_SEND_INTERRUPT:
231 if (!userio->running) {
232 dev_warn(userio_misc.this_device,
233 "The device must be registered before sending interrupts\n");
234 error = -ENODEV;
235 goto out;
236 }
237
238 serio_interrupt(userio->serio, cmd.data, 0);
239 break;
240
241 default:
242 error = -EOPNOTSUPP;
243 goto out;
244 }
245
246 out:
247 mutex_unlock(&userio->mutex);
248 return error ?: count;
249 }
250
userio_char_poll(struct file * file,poll_table * wait)251 static __poll_t userio_char_poll(struct file *file, poll_table *wait)
252 {
253 struct userio_device *userio = file->private_data;
254
255 poll_wait(file, &userio->waitq, wait);
256
257 if (userio->head != userio->tail)
258 return EPOLLIN | EPOLLRDNORM;
259
260 return 0;
261 }
262
263 static const struct file_operations userio_fops = {
264 .owner = THIS_MODULE,
265 .open = userio_char_open,
266 .release = userio_char_release,
267 .read = userio_char_read,
268 .write = userio_char_write,
269 .poll = userio_char_poll,
270 .llseek = no_llseek,
271 };
272
273 static struct miscdevice userio_misc = {
274 .fops = &userio_fops,
275 .minor = USERIO_MINOR,
276 .name = USERIO_NAME,
277 };
278 module_driver(userio_misc, misc_register, misc_deregister);
279
280 MODULE_ALIAS_MISCDEV(USERIO_MINOR);
281 MODULE_ALIAS("devname:" USERIO_NAME);
282
283 MODULE_AUTHOR("Stephen Chandler Paul <thatslyude@gmail.com>");
284 MODULE_DESCRIPTION("Virtual Serio Device Support");
285 MODULE_LICENSE("GPL");
286