Hi All,
I've written a custom device driver based on the usb-skeleton.c file in
the kernel source.
I want the driver to act in a similar way to when you read from a serial
port. ie, when you do this:
cat /dev/ttyS0
it will wait for data to appear on the port and output to the terminal.
It doesn't timeout, or close the connection when no data is available.
In my case the data source is an IN endpoint from a custom usb board.
The problem is how do I stop cat (or any other program) closing the
connection when the read function timesout (the condition when no data
is yet available).
I've tried checking to see if the return value from usb_bulk_msg is
ETIMEDOUT and returning 0 (no bytes read) from my read function rather
than the error, but cat still exits.
I've also tried setting the timeout parameter in usb_bulk_msg to 0 (wait
forever). But then you can't exit (^c) or even kill the program reading
from the port.
My read function is below.
Many thanks
Andy
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 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
info("usbDIO: Read retval: %d, count: %lu, bytesRead: %d",
retval, count, bytesRead);
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)
{
info("usbDIO: Read timeout");
// If timedout, just return 0 bytes read
retval = 0;
}
}
exit:
mutex_unlock(&deviceData->ioMutex);
return retval;
}
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