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Re: [RFC PATCH 1/3] net: Pad short frames to minimum size (60 bytes)

From: Bin Meng
Subject: Re: [RFC PATCH 1/3] net: Pad short frames to minimum size (60 bytes)
Date: Sat, 27 Feb 2021 10:00:48 +0800

On Sat, Feb 27, 2021 at 2:57 AM Peter Maydell <peter.maydell@linaro.org> wrote:
> On Fri, 26 Feb 2021 at 10:03, Bin Meng <bmeng.cn@gmail.com> 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.
> >
> > 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>
> > ---
> Is it better to do this here, or in the places which create
> network packets?

After looking at the eTSEC manual further, I think we should put these
codes in the send path.

> Doing it centrally has the advantage of
> being just one place to change which then means senders
> and receivers don't need to think about it. On the other
> hand it means we don't have any equivalent of really actually
> sending a short frame and having the modelled ethernet device
> implement the handling of the short frame.

Maybe the best choice would be each ethernet model duplicates the
codes in their send path?

I have not checked e1000 and vmxnet3 manual, but it seems workaround
this issue in the receive path is wrong.


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