#include <linux/fs.h>
#include <linux/cdev.h>
#include <linux/slab.h>
+#include <linux/mutex.h>
+#include <asm/uaccess.h>
+#include <linux/circ_buf.h>
+#include <linux/sched.h>
+#include <linux/completion.h>
MODULE_LICENSE("GPL");
+#define MAXLEN 4096
static dev_t devnum;
static struct cdev *dev;
+static const char default_greeting[] = "Hello, World!\n";
+
+static struct circ_buf *hello;
+static struct circ_buf hello_instance;
+static DEFINE_MUTEX(hello_mtx);
+static DECLARE_COMPLETION(hello_wait);
static int hello_open(struct inode *ino, struct file *fp)
{
- printk(KERN_DEBUG "Hello, World!\n");
+ return 0;
+}
+
+static ssize_t hello_read(struct file *fp, char __user *buf, size_t sz,
+ loff_t *pos)
+{
+ int r;
+ size_t fsz;
+ size_t ssz;
+ size_t len;
+ if (mutex_lock_interruptible(&hello_mtx))
+ return -ERESTARTSYS;
+ len = CIRC_CNT(hello->head, hello->tail, MAXLEN);
+ if (sz > len)
+ sz = len;
+ /* First, copy at most until the limit of the buffer */
+ fsz = min(sz, CIRC_CNT_TO_END(hello->head, hello->tail, MAXLEN));
+ r = copy_to_user(buf, hello->buf + hello->tail, fsz);
+ ssz = sz - fsz;
+ if (!r && !ssz)
+ r = copy_to_user(buf + fsz, hello->buf, ssz);
+ if (!r)
+ hello->tail = (hello->tail + sz) & ~MAXLEN;
+ mutex_unlock(&hello_mtx);
+ if (r)
+ return -EFAULT;
+ complete(&hello_wait);
+ return sz;
+}
+
+static ssize_t hello_write(struct file *fp, const char __user *buf, size_t sz,
+ loff_t *pos)
+{
+ int r;
+ size_t fsz;
+ size_t ssz;
+ size_t len;
+ if (mutex_lock_interruptible(&hello_mtx))
+ return -ERESTARTSYS;
+ len = CIRC_SPACE(hello->head, hello->tail, MAXLEN);
+ while (len == 0) {
+ mutex_unlock(&hello_mtx);
+ if (wait_for_completion_interruptible(&hello_wait))
+ return -ERESTARTSYS;
+ if (mutex_lock_interruptible(&hello_mtx))
+ return -ERESTARTSYS;
+ len = CIRC_SPACE(hello->head, hello->tail, MAXLEN);
+ }
+ if (sz > len)
+ sz = len;
+ fsz = min(sz, CIRC_SPACE_TO_END(hello->head, hello->tail, MAXLEN));
+ r = copy_from_user(hello->buf + hello->head, buf, fsz);
+ ssz = sz - fsz;
+ if (!r && !ssz)
+ r = copy_from_user(hello->buf, buf + fsz, ssz);
+ if (!r)
+ hello->head = (hello->head + sz) & ~MAXLEN;
+ mutex_unlock(&hello_mtx);
+ if (r)
+ return -EFAULT;
+ return sz;
+}
+
+static int hello_release(struct inode *ino, struct file *fp)
+{
return 0;
}
static const struct file_operations hello_fops = {
.owner = THIS_MODULE,
.open = hello_open,
+ .release = hello_release,
+ .read = hello_read,
+ .write = hello_write,
};
static int __init ch_init(void)
{
int r = 0;
+ hello = &hello_instance;
+ hello->buf = kzalloc(sizeof(*hello) + MAXLEN, GFP_KERNEL);
+ if (!hello) {
+ r = -ENOMEM;
+ goto out;
+ }
+ memcpy(hello->buf, default_greeting, sizeof(default_greeting));
+ hello->head = sizeof(default_greeting);
r = alloc_chrdev_region(&devnum, 0, 256, "hello");
if (r)
- goto out;
+ goto reg_out;
dev = cdev_alloc();
if (!dev) {
r = -ENOMEM;
r = cdev_add(dev, devnum, 256);
if (r)
goto add_out;
- printk(KERN_DEBUG "Allocate major %d\n", MAJOR(devnum));
return 0;
add_out:
kfree(dev);
cdev_out:
unregister_chrdev_region(devnum, 256);
+reg_out:
+ kfree(hello);
out:
return r;
}
static void __exit ch_exit(void)
{
cdev_del(dev);
- kfree(dev);
unregister_chrdev_region(devnum, 256);
+ kfree(hello->buf);
}
module_init(ch_init);