#include <linux/slab.h>
#include <linux/mutex.h>
#include <asm/uaccess.h>
+#include <linux/circ_buf.h>
MODULE_LICENSE("GPL");
-#define MAXLEN 4000
+#define MAXLEN 4096
static dev_t devnum;
static struct cdev *dev;
static const char default_greeting[] = "Hello, World!\n";
-struct hello_buffer {
- size_t len;
- char buffer[0];
-};
-static struct hello_buffer *hello;
+static struct circ_buf *hello;
+static struct circ_buf hello_instance;
static DEFINE_MUTEX(hello_mtx);
static int hello_open(struct inode *ino, struct file *fp)
{
- if (mutex_lock_interruptible(&hello_mtx))
- return -ERESTARTSYS;
- if (fp->f_flags & O_TRUNC) {
- memset(hello->buffer, 0, MAXLEN);
- hello->len = 0;
- }
- if (fp->f_flags & O_APPEND)
- fp->f_pos = hello->len;
- mutex_unlock(&hello_mtx);
return 0;
}
loff_t *pos)
{
int r;
+ size_t fsz;
+ size_t ssz;
+ size_t len;
if (mutex_lock_interruptible(&hello_mtx))
return -ERESTARTSYS;
- if (sz + *pos > hello->len)
- sz = hello->len - *pos;
- r = copy_to_user(buf, hello->buffer + *pos, sz);
+ 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;
- *pos += sz;
return sz;
}
loff_t *pos)
{
int r;
+ size_t fsz;
+ size_t ssz;
+ size_t len;
if (mutex_lock_interruptible(&hello_mtx))
return -ERESTARTSYS;
- if (sz + *pos > MAXLEN)
- sz = MAXLEN - *pos;
- r = copy_from_user(hello->buffer + *pos, buf, sz);
- if (r) {
- mutex_unlock(&hello_mtx);
- return -EFAULT;
- }
- *pos += sz;
- if (hello->len < *pos)
- hello->len = *pos;
+ 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 __init ch_init(void)
{
int r = 0;
- hello = kzalloc(sizeof(*hello) + MAXLEN, GFP_KERNEL);
+ hello = &hello_instance;
+ hello->buf = kzalloc(sizeof(*hello) + MAXLEN, GFP_KERNEL);
if (!hello) {
r = -ENOMEM;
goto out;
}
- memcpy(hello->buffer, default_greeting, sizeof(default_greeting));
- hello->len = sizeof(default_greeting);
+ memcpy(hello->buf, default_greeting, sizeof(default_greeting));
+ hello->head = sizeof(default_greeting);
r = alloc_chrdev_region(&devnum, 0, 256, "hello");
if (r)
goto reg_out;
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);