+ complete(&dev->bulk_in_completion);
+}
+
+static int skel_do_read_io(struct usb_skel *dev, size_t count)
+{
+ int rv;
+
+ /* prepare a read */
+ usb_fill_bulk_urb(dev->bulk_in_urb,
+ dev->udev,
+ usb_rcvbulkpipe(dev->udev,
+ dev->bulk_in_endpointAddr),
+ dev->bulk_in_buffer,
+ min(dev->bulk_in_size, count),
+ skel_read_bulk_callback,
+ dev);
+ /* tell everybody to leave the URB alone */
+ spin_lock_irq(&dev->err_lock);
+ dev->ongoing_read = 1;
+ spin_unlock_irq(&dev->err_lock);
+
+ /* do it */
+ rv = usb_submit_urb(dev->bulk_in_urb, GFP_KERNEL);
+ if (rv < 0) {
+ err("%s - failed submitting read urb, error %d",
+ __func__, rv);
+ dev->bulk_in_filled = 0;
+ rv = (rv == -ENOMEM) ? rv : -EIO;
+ spin_lock_irq(&dev->err_lock);
+ dev->ongoing_read = 0;
+ spin_unlock_irq(&dev->err_lock);
+ }
+
+ return rv;
+}
+
+static ssize_t skel_read(struct file *file, char *buffer, size_t count,
+ loff_t *ppos)
+{
+ struct usb_skel *dev;
+ int rv;
+ bool ongoing_io;
+
+ dev = (struct usb_skel *)file->private_data;
+
+ /* if we cannot read at all, return EOF */
+ if (!dev->bulk_in_urb || !count)
+ return 0;
+
+ /* no concurrent readers */
+ rv = mutex_lock_interruptible(&dev->io_mutex);
+ if (rv < 0)
+ return rv;
+
+ if (!dev->interface) { /* disconnect() was called */
+ rv = -ENODEV;
+ goto exit;
+ }
+
+ /* if IO is under way, we must not touch things */
+retry:
+ spin_lock_irq(&dev->err_lock);
+ ongoing_io = dev->ongoing_read;
+ spin_unlock_irq(&dev->err_lock);
+
+ if (ongoing_io) {
+ /* nonblocking IO shall not wait */
+ if (file->f_flags & O_NONBLOCK) {
+ rv = -EAGAIN;
+ goto exit;
+ }
+ /*
+ * IO may take forever
+ * hence wait in an interruptible state
+ */
+ rv = wait_for_completion_interruptible(&dev->bulk_in_completion);
+ if (rv < 0)
+ goto exit;
+ /*
+ * by waiting we also semiprocessed the urb
+ * we must finish now
+ */
+ dev->bulk_in_copied = 0;
+ dev->processed_urb = 1;
+ }
+
+ if (!dev->processed_urb) {
+ /*
+ * the URB hasn't been processed
+ * do it now
+ */
+ wait_for_completion(&dev->bulk_in_completion);
+ dev->bulk_in_copied = 0;
+ dev->processed_urb = 1;
+ }
+
+ /* errors must be reported */
+ rv = dev->errors;
+ if (rv < 0) {
+ /* any error is reported once */
+ dev->errors = 0;
+ /* to preserve notifications about reset */
+ rv = (rv == -EPIPE) ? rv : -EIO;
+ /* no data to deliver */
+ dev->bulk_in_filled = 0;
+ /* report it */
+ goto exit;
+ }
+
+ /*
+ * if the buffer is filled we may satisfy the read
+ * else we need to start IO
+ */
+
+ if (dev->bulk_in_filled) {
+ /* we had read data */
+ size_t available = dev->bulk_in_filled - dev->bulk_in_copied;
+ size_t chunk = min(available, count);
+
+ if (!available) {
+ /*
+ * all data has been used
+ * actual IO needs to be done
+ */
+ rv = skel_do_read_io(dev, count);
+ if (rv < 0)
+ goto exit;
+ else
+ goto retry;
+ }
+ /*
+ * data is available
+ * chunk tells us how much shall be copied
+ */
+
+ if (copy_to_user(buffer,
+ dev->bulk_in_buffer + dev->bulk_in_copied,
+ chunk))
+ rv = -EFAULT;
+ else
+ rv = chunk;
+
+ dev->bulk_in_copied += chunk;
+
+ /*
+ * if we are asked for more than we have,
+ * we start IO but don't wait
+ */
+ if (available < count)
+ skel_do_read_io(dev, count - chunk);
+ } else {
+ /* no data in the buffer */
+ rv = skel_do_read_io(dev, count);
+ if (rv < 0)
+ goto exit;
+ else if (!(file->f_flags & O_NONBLOCK))
+ goto retry;
+ rv = -EAGAIN;
+ }
+exit:
+ mutex_unlock(&dev->io_mutex);
+ return rv;