Some drivers (Linux' 8139too among them) rely on the NIC injecting an interrupt
in the event of a receive buffer overflow and, accordingly, set the RxOverflow
bit in the interrupt mask. Unfortunately rtl8139's can_receive method ignores
the RxOverflow flag, which may lead to a situation where rtl8139 stops receiving
packets (can_receive returns 0) when the receive buffer becomes full.
If the driver eventually read from the receive buffer or reset the card the
emulator could recover from this situation. However some implementations only
do this upon receiving an interrupt with either RxOK or RxOverflow set in the
ISR; interrupt that will never come because QEMU's flow control mechanisms would
prevent rtl8139 from receiving any packet.
Letting packets go through when the overflow interrupt is enabled makes the
QEMU emulator compliant to the spec and solves the problem.
This patch should fix a relatively common (in our experience) network stall
observed when running enterprise distros with rtl8139 as the NIC; in some cases
the 8139too device driver gets loaded and when under heavy load the network
eventually stops working.
Reported-by: Hayato Kakuta<address@hidden>
Tested-by: Hayato Kakuta<address@hidden>
Signed-off-by: Fernando Luis Vazquez Cao<address@hidden>
---
diff -urNp qemu-kvm-orig/hw/rtl8139.c qemu-kvm/hw/rtl8139.c
--- qemu-kvm-orig/hw/rtl8139.c 2012-01-12 20:55:27.000000000 +0900
+++ qemu-kvm/hw/rtl8139.c 2012-01-18 17:20:12.000000000 +0900
@@ -824,7 +824,7 @@ static int rtl8139_can_receive(VLANClien
} else {
avail = MOD2(s->RxBufferSize + s->RxBufPtr - s->RxBufAddr,
s->RxBufferSize);
- return (avail == 0 || avail>= 1514);
+ return (avail == 0 || avail>= 1514 || (s->IntrMask& RxOverflow));
}
}