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Re: [PATCH v5 00/12] net: Pad short frames for network backends
From: |
Bin Meng |
Subject: |
Re: [PATCH v5 00/12] net: Pad short frames for network backends |
Date: |
Mon, 22 Mar 2021 09:28:40 +0800 |
On Wed, Mar 17, 2021 at 2:26 PM Bin Meng <bmeng.cn@gmail.com> wrote:
>
> The minimum Ethernet frame length is 60 bytes. For short frames with
> smaller length like ARP packets (only 42 bytes), on a real world NIC
> it can choose either padding its length to the minimum required 60
> bytes, or sending it out directly to the wire. Such behavior can be
> hardcoded or controled by a register bit. Similarly on the receive
> path, NICs can choose either dropping such short frames directly or
> handing them over to software to handle.
>
> On the other hand, for the network backends like SLiRP/TAP, they
> don't expose a way to control the short frame behavior. As of today
> they just send/receive data from/to the other end connected to them,
> which means any sized packet is acceptable. So they can send and
> receive short frames without any problem. It is observed that ARP
> packets sent from SLiRP/TAP are 42 bytes, and SLiRP/TAP just send
> these ARP packets to the other end which might be a NIC model that
> does not allow short frames to pass through.
>
> To provide better compatibility, for packets sent from QEMU network
> backends like SLiRP/TAP, we change to pad short frames before sending
> it out to the other end, if the other end does not forbid it via the
> nc->do_not_pad flag. This ensures a backend as an Ethernet sender
> does not violate the spec. But with this change, the behavior of
> dropping short frames from SLiRP/TAP interfaces in the NIC model
> cannot be emulated because it always receives a packet that is spec
> complaint. The capability of sending short frames from NIC models is
> still supported and short frames can still pass through SLiRP/TAP.
>
> This series should be able to fix the issue as reported with some
> NIC models before, that ARP requests get dropped, preventing the
> guest from becoming visible on the network. It was workarounded in
> these NIC models on the receive path, that when a short frame is
> received, it is padded up to 60 bytes.
>
> Changes in v5:
> - minor update on commit message
> - update the eth_pad_short_frame() comment
>
Ping?
- [PATCH v5 03/12] net: Pad short frames to minimum size before sending from SLiRP/TAP, (continued)
- [PATCH v5 03/12] net: Pad short frames to minimum size before sending from SLiRP/TAP, Bin Meng, 2021/03/17
- [PATCH v5 04/12] hw/net: virtio-net: Initialize nc->do_not_pad to true, Bin Meng, 2021/03/17
- [PATCH v5 05/12] hw/net: e1000: Remove the logic of padding short frames in the receive path, Bin Meng, 2021/03/17
- [PATCH v5 06/12] hw/net: vmxnet3: Remove the logic of padding short frames in the receive path, Bin Meng, 2021/03/17
- [PATCH v5 08/12] hw/net: ne2000: Remove the logic of padding short frames in the receive path, Bin Meng, 2021/03/17
- [PATCH v5 07/12] hw/net: i82596: Remove the logic of padding short frames in the receive path, Bin Meng, 2021/03/17
- [PATCH v5 09/12] hw/net: pcnet: Remove the logic of padding short frames in the receive path, Bin Meng, 2021/03/17
- [PATCH v5 10/12] hw/net: rtl8139: Remove the logic of padding short frames in the receive path, Bin Meng, 2021/03/17
- [PATCH v5 11/12] hw/net: sungem: Remove the logic of padding short frames in the receive path, Bin Meng, 2021/03/17
- [PATCH v5 12/12] hw/net: sunhme: Remove the logic of padding short frames in the receive path, Bin Meng, 2021/03/17
- Re: [PATCH v5 00/12] net: Pad short frames for network backends,
Bin Meng <=
- Re: [PATCH v5 00/12] net: Pad short frames for network backends, Jason Wang, 2021/03/22