Added len attribute.

diff --git a/hellochar.c b/hellochar.c
index e601e38..940bfeb 100644 (file)
--- a/hellochar.c
+++ b/hellochar.c
@@ -117,6 +117,18 @@ static const struct file_operations hello_fops = {
        .write = hello_write,
 };
 
+static ssize_t hello_len_show(struct device *dev, struct device_attribute *attr,
+       char *buffer)
+{
+       size_t len = CIRC_CNT(hello->head, hello->tail, MAXLEN);
+       return sprintf(buffer, "%d\n", len);
+}
+
+static const struct device_attribute hello_len_attr = {
+       .attr = { .name = "len", .mode = 0444, },
+       .show = hello_len_show,
+};
+
 static struct class *hello_class;
 static struct device *hello_dev;
 
@@ -144,6 +156,9 @@ static int __init ch_init(void)
                r = -ENODEV;
                goto dev_out;
        }
+       r = device_create_file(hello_dev, &hello_len_attr);
+       if (r)
+               goto file_out;
        dev = cdev_alloc();
        if (!dev) {
                r = -ENOMEM;
@@ -157,6 +172,8 @@ static int __init ch_init(void)
 add_out:
        kfree(dev);
 cdev_out:
+       device_remove_file(hello_dev, &hello_len_attr);
+file_out:
        device_destroy(hello_class, devnum);
 dev_out:
        unregister_chrdev_region(devnum, 256);
@@ -171,6 +188,7 @@ out:
 static void __exit ch_exit(void)
 {
        cdev_del(dev);
+       device_remove_file(hello_dev, &hello_len_attr);
        device_destroy(hello_class, devnum);
        unregister_chrdev_region(devnum, 256);
        kfree(hello->buf);