2 * Copyright (C) 2010 Thadeu Lima de Souza Cascardo <cascardo@holoscopio.com>
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License as published by
6 * the Free Software Foundation; either version 2 of the License, or
7 * (at your option) any later version.
9 * This program is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 * GNU General Public License for more details.
14 * You should have received a copy of the GNU General Public License along
15 * with this program; if not, write to the Free Software Foundation, Inc.,
16 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
19 #include <linux/module.h>
21 #include <linux/cdev.h>
22 #include <linux/slab.h>
23 #include <linux/mutex.h>
24 #include <asm/uaccess.h>
25 #include <linux/circ_buf.h>
27 MODULE_LICENSE("GPL");
31 static struct cdev *dev;
32 static const char default_greeting[] = "Hello, World!\n";
34 static struct circ_buf *hello;
35 static struct circ_buf hello_instance;
36 static DEFINE_MUTEX(hello_mtx);
38 static int hello_open(struct inode *ino, struct file *fp)
43 static ssize_t hello_read(struct file *fp, char __user *buf, size_t sz,
50 if (mutex_lock_interruptible(&hello_mtx))
52 len = CIRC_CNT(hello->head, hello->tail, MAXLEN);
55 /* First, copy at most until the limit of the buffer */
56 fsz = min(sz, CIRC_CNT_TO_END(hello->head, hello->tail, MAXLEN));
57 r = copy_to_user(buf, hello->buf + hello->tail, fsz);
60 r = copy_to_user(buf + fsz, hello->buf, ssz);
62 hello->tail = (hello->tail + sz) & ~MAXLEN;
63 mutex_unlock(&hello_mtx);
69 static ssize_t hello_write(struct file *fp, const char __user *buf, size_t sz,
76 if (mutex_lock_interruptible(&hello_mtx))
78 len = CIRC_SPACE(hello->head, hello->tail, MAXLEN);
81 fsz = min(sz, CIRC_SPACE_TO_END(hello->head, hello->tail, MAXLEN));
82 r = copy_from_user(hello->buf + hello->head, buf, fsz);
85 r = copy_from_user(hello->buf, buf + fsz, ssz);
87 hello->head = (hello->head + sz) & ~MAXLEN;
88 mutex_unlock(&hello_mtx);
94 static int hello_release(struct inode *ino, struct file *fp)
99 static const struct file_operations hello_fops = {
100 .owner = THIS_MODULE,
102 .release = hello_release,
104 .write = hello_write,
107 static int __init ch_init(void)
110 hello = &hello_instance;
111 hello->buf = kzalloc(sizeof(*hello) + MAXLEN, GFP_KERNEL);
116 memcpy(hello->buf, default_greeting, sizeof(default_greeting));
117 hello->head = sizeof(default_greeting);
118 r = alloc_chrdev_region(&devnum, 0, 256, "hello");
126 dev->ops = &hello_fops;
127 r = cdev_add(dev, devnum, 256);
134 unregister_chrdev_region(devnum, 256);
141 static void __exit ch_exit(void)
144 unregister_chrdev_region(devnum, 256);
148 module_init(ch_init);
149 module_exit(ch_exit);