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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>
This commit is contained in:
Hans de Goede 2012-10-31 13:47:10 +01:00 committed by Gerd Hoffmann
parent a552a966f1
commit 579967bea6
1 changed files with 5 additions and 2 deletions
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7
hw/usb/combined-packet.c
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@ -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) {