On Thu, 9 Feb 2006, mail mail wrote:
> Hi,
>
> I wrote a USB smart card device driver for kernel 2.6. I can run it
> with no error on kernel 2.6.11, but fail on kernel 2.6.8 and 2.6.14.
> Now I can locate that the problem exist in copy_to_user() system call.
> My environment is Debian Sarge 2.6.8-2-386.
>
> In skel_read(), there are:
> ......
> /* do a blocking bulk read to get data from the device */
> retval = usb_bulk_msg(dev->udev,
> usb_rcvbulkpipe(dev->udev,
> dev->bulk_in_endpointAddr),
> dev->bulk_in_buffer,
> min(dev->bulk_in_size, count),
> //dev->bulk_in_size,
> &count, HZ*10);
>
> info("retval of skel_read %d", retval);
>
> /* if the read was successful, copy the data to userspace */
> if (!retval) {
> if (copy_to_user(buffer, dev->bulk_in_buffer, count)) {
> info("fault");
> retval = -EFAULT;
> }
> else
> {
> retval = count;
> info("good");
> info("retval of copy_to_user is %d", retval);
> }
> }
> ......
>
> The output of the above code is :
> Feb 9 15:03:36 localhost kernel: /root/bnewDT3500/kernel/DT3500.c:
> retval of skel_read 0
> Feb 9 15:03:36 localhost kernel: /root/bnewDT3500/kernel/DT3500.c: good
> Feb 9 15:03:36 localhost kernel: /root/bnewDT3500/kernel/DT3500.c:
> retval of copy_to_user is 10
>
> In the right case, the return value of copy_to_user should be 4 on my
> PC, and 4 is also the value on kernel 2.6.11 which can run the driver
> successfully.
Without getting too involved in this, I'd like to point out that your
driver fragment doesn't print out the value returned by copy_to_user. It
prints out the value of count, which is the actual transfer length from
usb_bulk_msg. The fact that you see the "retval of copy_to_user" message
at all means that copy_to_user actually returned 0.
Alan Stern
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