combined-packet: Add a workaround for Linux usbfs + live migration

Older versions (anything but the latest) of Linux usbfs + libusb(x),
will submit larger (bulk) transfers split into multiple 16k submissions,
which means that rather then all tds getting linked into the queue in
one atomic operarion they get linked in a bunch at a time, which could
cause problems if:
1) We scan the queue while libusb is in the middle of submitting a split
   bulk transfer
2) While this bulk transfer is pending we migrate to another host.

The problem is that after 2, the new host will rescan the queue and
combine the packets in one large transfer, where as 1) has caused the
original host to see them as 2 transfers. This patch fixes this by stopping
combinging if we detect a 16k transfer with its int_req flag set.

This should not adversely effect performance for other cases as:
1) Linux never sets the interrupt flag on packets other then the last
2) Windows does set the in_req flag on each td, but will submit large
transfers in 20k tds thus never triggering the check

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

diff --git a/hw/usb/combined-packet.c b/hw/usb/combined-packet.c
index 652bf02628cee5dc42d18d222fbdfb4eb0f75e8a..3904e7163439de11e6cf5397e2e8189672d3cd00 100644 (file)
--- a/hw/usb/combined-packet.c
+++ b/hw/usb/combined-packet.c
@@ -117,7 +117,7 @@ void usb_ep_combine_input_packets(USBEndpoint *ep)
 {
     USBPacket *p, *u, *next, *prev = NULL, *first = NULL;
     USBPort *port = ep->dev->port;
-    int ret;
+    int ret, totalsize;
 
     assert(ep->pipeline);
     assert(ep->pid == USB_TOKEN_IN);
@@ -161,8 +161,11 @@ void usb_ep_combine_input_packets(USBEndpoint *ep)
         }
 
         /* Is this packet the last one of a (combined) transfer? */
+        totalsize = (p->combined) ? p->combined->iov.size : p->iov.size;
         if ((p->iov.size % ep->max_packet_size) != 0 || !p->short_not_ok ||
-                next == NULL) {
+                next == NULL ||
+                /* Work around for Linux usbfs bulk splitting + migration */
+                (totalsize == 16348 && p->int_req)) {
             ret = usb_device_handle_data(ep->dev, first);
             assert(ret == USB_RET_ASYNC);
             if (first->combined) {