Re: [Qemu-devel] [PATCH 1/2] fsl_etsec: Pad short payloads with zeros

[Jason Wang <jasowang@redhat.com>]

On 2016年11月29日 02:13, Andrey Smirnov wrote:
> Depending on QEMU network setup it is possible for us to receive a
> complete Ethernet packet that is less 64 bytes long. One such example is
> when QEMU is configured to use a standalone TAP device (not set to be a
> part of any bridge) receives and ARP packet. In cases like that we need
> to add more than just 4-bytes of CRC padding and ensure that our payload
> is at least 60 bytes long, such that, when combined with CRC padding
> bytes the resulting size is at least 802.3 minimum MTU bytes
> long (64). Failing to do that results in code in etsec_walk_rx_ring()
> setting BD_RX_SH which, in turn, makes corresponding Linux driver of
> emulated host to reject buffer as a runt packet
>
> Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
> ---
>   hw/net/fsl_etsec/rings.c | 7 +++++++
>   1 file changed, 7 insertions(+)
>
> diff --git a/hw/net/fsl_etsec/rings.c b/hw/net/fsl_etsec/rings.c
> index 79d2f14..1434c91 100644
> --- a/hw/net/fsl_etsec/rings.c
> +++ b/hw/net/fsl_etsec/rings.c
> @@ -474,6 +474,13 @@ static void rx_init_frame(eTSEC *etsec, const uint8_t *buf, size_t size)
>       /* CRC padding (We don't have to compute the CRC) */
>       etsec->rx_padding = 4;
>   
> +    /*
> +     * Ensure that payload length + CRC length is at least 802.3
> +     * minimum MTU size bytes long (64)
> +     */
> +    if (etsec->rx_buffer_len < 60)
> +        etsec->rx_padding += 60 - etsec->rx_buffer_len;
> +
>       etsec->rx_first_in_frame = 1;
>       etsec->rx_remaining_data = etsec->rx_buffer_len;
>       RING_DEBUG("%s: rx_buffer_len:%u rx_padding+crc:%u\n", __func__,

Applied, thanks.