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);
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
{
err("usbDIO: %s - Read failed, error %d", __FUNCTION__, retval);
}
exit:
mutex_unlock(&deviceData->ioMutex);
return retval;
}
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