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Re: [RFC PATCH 1/3] net: Pad short frames to minimum size (60 bytes)
From: |
Philippe Mathieu-Daudé |
Subject: |
Re: [RFC PATCH 1/3] net: Pad short frames to minimum size (60 bytes) |
Date: |
Fri, 26 Feb 2021 11:29:07 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.0 |
On 2/26/21 11:03 AM, Bin Meng wrote:
> From: Bin Meng <bin.meng@windriver.com>
>
> The minimum Ethernet frame length is 60 bytes, and we should pad
> frames whose length is smaller to the minimum size.
>
> This commit fixes the issue as seen with various ethernet models,
> that ARP requests get dropped, preventing the guest from becoming
> visible on the network.
Is it also used in commit 18995b9808d ("Send a RARP packet after
migration.")?
> The following 2 commits that attempted to workaround this issue
> in e1000 and vmxenet3 before, should be reverted.
>
> commit 78aeb23eded2 ("e1000: Pad short frames to minimum size (60 bytes)")
> commit 40a87c6c9b11 ("vmxnet3: Pad short frames to minimum size (60 bytes)")
>
> Signed-off-by: Bin Meng <bin.meng@windriver.com>
> ---
>
> net/net.c | 9 +++++++++
> 1 file changed, 9 insertions(+)
>
> diff --git a/net/net.c b/net/net.c
> index b038370..34004da 100644
> --- a/net/net.c
> +++ b/net/net.c
> @@ -638,6 +638,7 @@ static ssize_t
> qemu_send_packet_async_with_flags(NetClientState *sender,
> NetPacketSent *sent_cb)
> {
> NetQueue *queue;
> + uint8_t min_buf[60];
Can you add a definition instead of a magic value?
Maybe ETH_FRAME_MIN_LEN in "net/eth.h"?
> int ret;
>
> #ifdef DEBUG_NET
> @@ -649,6 +650,14 @@ static ssize_t
> qemu_send_packet_async_with_flags(NetClientState *sender,
> return size;
> }
>
> + /* Pad to minimum Ethernet frame length */
> + if (size < sizeof(min_buf)) {
> + memcpy(min_buf, buf, size);
> + memset(&min_buf[size], 0, sizeof(min_buf) - size);
> + buf = min_buf;
> + size = sizeof(min_buf);
> + }
> +
> /* Let filters handle the packet first */
> ret = filter_receive(sender, NET_FILTER_DIRECTION_TX,
> sender, flags, buf, size, sent_cb);
>