Re: [Qemu-devel] [PATCH] rtl8139: honor RxOverflow flag in can_receive method

[Anthony Liguori <aliguori@us.ibm.com>]

On 01/29/2012 08:17 PM, Fernando Luis Vázquez Cao wrote:
> 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<kakuta.hayato@oss.ntt.co.jp>
> Tested-by: Hayato Kakuta<kakuta.hayato@oss.ntt.co.jp>
> Signed-off-by: Fernando Luis Vazquez Cao<fernando@oss.ntt.co.jp>

Applied.  Thanks.

Regards,

Anthony Liguori

> ---
>
> 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));
>       }
>   }
>
>
>
>
>