Hi Alan,
On 11/8/2017 9:23 PM, Alan Stern wrote:
> The USB kerneldoc says that the actual_length field "is read in
> non-iso completion functions", but the usbfs driver uses it for all
> URB types in processcompl(). Since not all of the host controller
> drivers set actual_length for isochronous URBs, programs using usbfs
> with some host controllers don't work properly. For example, Minas
> reports that a USB camera controlled by libusb doesn't work properly
> with a dwc2 controller.
Issue reported not by me, but by William Wu (wlf <wulf@xxxxxxxxxxxxxx>)
>
> It doesn't seem worthwhile to change the HCDs and the documentation,
> since the in-kernel USB class drivers evidently don't rely on
> actual_length for isochronous transfers. The easiest solution is for
> usbfs to calculate the actual_length value for itself, by adding up
> the lengths of the individual packets in an isochronous transfer.
>
> Signed-off-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
> CC: Minas Harutyunyan <Minas.Harutyunyan@xxxxxxxxxxxx>
> Reported-and-tested-by: wlf <wulf@xxxxxxxxxxxxxx>
> CC: <stable@xxxxxxxxxxxxxxx>
>
> ---
>
>
> [as1853]
>
>
> drivers/usb/core/devio.c | 14 ++++++++++++++
> 1 file changed, 14 insertions(+)
>
> Index: usb-4.x/drivers/usb/core/devio.c
> ===================================================================
> --- usb-4.x.orig/drivers/usb/core/devio.c
> +++ usb-4.x/drivers/usb/core/devio.c
> @@ -1828,6 +1828,18 @@ static int proc_unlinkurb(struct usb_dev
> return 0;
> }
>
> +static void compute_isochronous_actual_length(struct urb *urb)
> +{
> + unsigned int i;
> +
> + if (urb->number_of_packets > 0) {
> + urb->actual_length = 0;
> + for (i = 0; i < urb->number_of_packets; i++)
> + urb->actual_length +=
> + urb->iso_frame_desc[i].actual_length;
> + }
> +}
> +
> static int processcompl(struct async *as, void __user * __user *arg)
> {
> struct urb *urb = as->urb;
> @@ -1835,6 +1847,7 @@ static int processcompl(struct async *as
> void __user *addr = as->userurb;
> unsigned int i;
>
> + compute_isochronous_actual_length(urb);
> if (as->userbuffer && urb->actual_length) {
> if (copy_urb_data_to_user(as->userbuffer, urb))
> goto err_out;
> @@ -2003,6 +2016,7 @@ static int processcompl_compat(struct as
> void __user *addr = as->userurb;
> unsigned int i;
>
> + compute_isochronous_actual_length(urb);
> if (as->userbuffer && urb->actual_length) {
> if (copy_urb_data_to_user(as->userbuffer, urb))
> return -EFAULT;
>
>
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