Re: [Qemu-devel] [PATCH] Add USB sys file-system support (v2)

[Jason Wessel]

TJ wrote:
> 
> I agree, maybe it is the serial character-based devices. As I can
> reproduce it with a different VID:PID of the same class it seems more
> likely.
> 


The usb serial devices do not appear to have an alternate interface
and this particular ioctl will always fail for the usb serial driver
in the host kernel.  It might not be the right way to fix it (see
patch below), but it does cause the device to actually work correctly
in the guest.

At this point I was able to use the rs232 usb dongle in the guest
looped back to the rs232 port on the host's motherboard via a null
modem.  This means I can now debug the usb linux console driver with
qemu. :-)

Many thanks for your adding in the code to read from /dev/bus/usb.

Jason.

---
 usb-linux.c |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

--- a/usb-linux.c
+++ b/usb-linux.c
@@ -548,8 +548,7 @@ static int usb_linux_update_endp_table(U
 
         ret = ioctl(s->fd, USBDEVFS_CONTROL, &ct);
         if (ret < 0) {
-            perror("usb_linux_update_endp_table");
-            return 1;
+                alt_interface = interface;
         }
 
         /* the current interface descriptor is the active interface