netdev - Re: [PATCH V5 net-next 0/6] ethtool: add support to set/get tx copybreak buf size and rx buf len

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Date:   Sat, 30 Oct 2021 19:58:55 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Guangbin Huang <huangguangbin2@...wei.com>
Cc:     davem@...emloft.net, kuba@...nel.org, mkubecek@...e.cz,
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Subject: Re: [PATCH V5 net-next 0/6] ethtool: add support to set/get tx
 copybreak buf size and rx buf len

> Rx buf len is buffer length of each rx BD. Use ethtool -g command to get
> it, and ethtool -G command to set it, examples are as follow:
> 
> 1. set rx buf len to 4096
> $ ethtool -G eth1 rx-buf-len 4096
> 
> 2. get rx buf len
> $ ethtool -g eth1
> ...
> RX Buf Len:     4096

How does this interact with MTU? If i have an MTU of 1500, and i set
the rx-buf-len to 1000, can i expect all frames to the discarded?
Should the core return -EINVAL? Or do you think some hardware will
simply allocate two buffers and scatter/gather over them? Which
implies that drivers which cannot SG must check if the rx-buf-len is
less than the MTU and return -EINVAL?

     Andrew