Write function.

diff --git a/hellochar.c b/hellochar.c
index c95100e..1649fe3 100644 (file)
--- a/hellochar.c
+++ b/hellochar.c
@@ -20,9 +20,11 @@
 #include <linux/fs.h>
 #include <linux/cdev.h>
 #include <linux/slab.h>
+#include <asm/uaccess.h>
 
 MODULE_LICENSE("GPL");
 
+#define MAXLEN 4000
 static dev_t devnum;
 static struct cdev *dev;
 static const char default_greeting[] = "Hello, World!\n";
@@ -34,17 +36,43 @@ struct hello_buffer {
 
 static int hello_open(struct inode *ino, struct file *fp)
 {
-       struct hello_buffer *hello = kmalloc(sizeof(*hello) + 4000, GFP_KERNEL);
+       struct hello_buffer *hello = kzalloc(sizeof(*hello) + MAXLEN, GFP_KERNEL);
        if (!hello)
                return -ENOMEM;
-       hello->private_data = hello;
+       memcpy(hello->buffer, default_greeting, sizeof(default_greeting));
+       hello->len = sizeof(default_greeting);
+       fp->private_data = hello;
        return 0;
 }
 
 static ssize_t hello_read(struct file *fp, char __user *buf, size_t sz,
        loff_t *pos)
 {
-       return 0;
+       struct hello_buffer *hello = fp->private_data;
+       int r;
+       if (sz + *pos > hello->len)
+               sz = hello->len - *pos;
+       r = copy_to_user(buf, hello->buffer + *pos, sz);
+       if (r)
+               return -EFAULT;
+       *pos += sz;
+       return sz;
+}
+
+static ssize_t hello_write(struct file *fp, const char __user *buf, size_t sz,
+       loff_t *pos)
+{
+       struct hello_buffer *hello = fp->private_data;
+       int r;
+       if (sz + *pos > MAXLEN)
+               sz = MAXLEN - *pos;
+       r = copy_from_user(hello->buffer + *pos, buf, sz);
+       if (r)
+               return -EFAULT;
+       *pos += sz;
+       if (hello->len < *pos)
+               hello->len = *pos;
+       return sz;
 }
 
 static int hello_release(struct inode *ino, struct file *fp)
@@ -58,6 +86,7 @@ static const struct file_operations hello_fops = {
        .open = hello_open,
        .release = hello_release,
        .read = hello_read,
+       .write = hello_write,
 };
 
 static int __init ch_init(void)