virtio: virtconsole: Use seq_file for debugfs operations

Simplifies the code and is more conventional to what's used in the rest
of the kernel for debugfs ops.
Signed-off-by: Tuomas Tynkkynen <tuomas@tuxera.com>
Reviewed-by: Amit Shah <amit@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/char/virtio_console.c

@@ -1309,51 +1309,35 @@ static const struct attribute_group port_attribute_group = {
 	.attrs = port_sysfs_entries,
 };
 
-static ssize_t debugfs_read(struct file *filp, char __user *ubuf,
-			    size_t count, loff_t *offp)
+static int debugfs_show(struct seq_file *s, void *data)
 {
-	struct port *port;
-	char *buf;
-	ssize_t ret, out_offset, out_count;
-
-	out_count = 1024;
-	buf = kmalloc(out_count, GFP_KERNEL);
-	if (!buf)
-		return -ENOMEM;
-
-	port = filp->private_data;
-	out_offset = 0;
-	out_offset += snprintf(buf + out_offset, out_count,
-			       "name: %s\n", port->name ? port->name : "");
-	out_offset += snprintf(buf + out_offset, out_count - out_offset,
-			       "guest_connected: %d\n", port->guest_connected);
-	out_offset += snprintf(buf + out_offset, out_count - out_offset,
-			       "host_connected: %d\n", port->host_connected);
-	out_offset += snprintf(buf + out_offset, out_count - out_offset,
-			       "outvq_full: %d\n", port->outvq_full);
-	out_offset += snprintf(buf + out_offset, out_count - out_offset,
-			       "bytes_sent: %lu\n", port->stats.bytes_sent);
-	out_offset += snprintf(buf + out_offset, out_count - out_offset,
-			       "bytes_received: %lu\n",
-			       port->stats.bytes_received);
-	out_offset += snprintf(buf + out_offset, out_count - out_offset,
-			       "bytes_discarded: %lu\n",
-			       port->stats.bytes_discarded);
-	out_offset += snprintf(buf + out_offset, out_count - out_offset,
-			       "is_console: %s\n",
+	struct port *port = s->private;
+
+	seq_printf(s, "name: %s\n", port->name ? port->name : "");
+	seq_printf(s, "guest_connected: %d\n", port->guest_connected);
+	seq_printf(s, "host_connected: %d\n", port->host_connected);
+	seq_printf(s, "outvq_full: %d\n", port->outvq_full);
+	seq_printf(s, "bytes_sent: %lu\n", port->stats.bytes_sent);
+	seq_printf(s, "bytes_received: %lu\n", port->stats.bytes_received);
+	seq_printf(s, "bytes_discarded: %lu\n", port->stats.bytes_discarded);
+	seq_printf(s, "is_console: %s\n",
 		   is_console_port(port) ? "yes" : "no");
-	out_offset += snprintf(buf + out_offset, out_count - out_offset,
-			       "console_vtermno: %u\n", port->cons.vtermno);
+	seq_printf(s, "console_vtermno: %u\n", port->cons.vtermno);
 
-	ret = simple_read_from_buffer(ubuf, count, offp, buf, out_offset);
-	kfree(buf);
-	return ret;
+	return 0;
+}
+
+static int debugfs_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, debugfs_show, inode->i_private);
 }
 
 static const struct file_operations port_debugfs_ops = {
 	.owner = THIS_MODULE,
-	.open  = simple_open,
-	.read  = debugfs_read,
+	.open = debugfs_open,
+	.read = seq_read,
+	.llseek = seq_lseek,
+	.release = single_release,
 };
 
 static void set_console_size(struct port *port, u16 rows, u16 cols)