Am Dienstag 06 November 2007 schrieb Andy Greensted:
> Alan Stern wrote:
> > There are two possible approaches. The easy way is just to use a very,
> > very long timeout. Alternatively, when a timeout does occur don't
> > return to the user; instead loop back and submit another usb_bulk_msg.
> >
> > Alan Stern
>
> As suggested, I've modified my driver to continually retry a
> usb_bulk_msg if a timeout occurs (ETIMEDOUT is returned). My read
> function now only returns if data has been read, or another error type
> occurs.
>
> The only problem now is that a program reading from my device will not
> respond to a ^C (or kill). I guess it's stuck in the read loop waiting
> for data!
>
> Any suggestions? Do I need to adjust the way the 'locking' is working
>
> Here is the modified code:
>
> static ssize_t usbDIO_read(struct file *file, char __user *buffer,
> size_t count, loff_t *ppos)
> {
> struct usbDIO_deviceData *deviceData;
> int retval = 0;
> int bytesRead;
>
> deviceData = (struct usbDIO_deviceData *)file->private_data;
>
> mutex_lock(&deviceData->ioMutex);
>
> if (!deviceData->interface)
> {
> // disconnect() was called
> retval = -ENODEV;
> goto exit;
> }
>
> do
> {
> // Do a blocking bulk read to get data from the device
> retval = usb_bulk_msg(deviceData->device,
> usb_rcvbulkpipe(deviceData->device,
> deviceData->bulk_in_endpointAddr),
> deviceData->bulk_in_buffer,
> min(deviceData->bulk_in_size, count),
> &bytesRead,
> HZ); // 1 second
> }
> while(retval == -ETIMEDOUT);
while (retval == -ETIMEDOUT && !signal_pending(current));
>
> if (retval == 0)
> {
> // If successful, copy the data to userspace
> if (copy_to_user(buffer, deviceData->bulk_in_buffer,
> count)) retval = -EFAULT;
> else retval = bytesRead;
> }
> else
> {
if (retval == -ETIMEDOUT && signal_pending(current))
retval = bytesRead ? bytesRead : -EINTR;
else
> err("usbDIO: %s - Read failed, error %d", __FUNCTION__, retval);
> }
>
> exit:
> mutex_unlock(&deviceData->ioMutex);
> return retval;
> }
Regards
Oliver
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