linux-kernel - Re: [PATCH] drivers/net/wan/lapbether: Use needed_headroom instead of hard_header

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Date:   Mon, 27 Jul 2020 12:41:16 -0700
From:   Xie He <xie.he.0141@...il.com>
To:     Cong Wang <xiyou.wangcong@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, Linux X25 <linux-x25@...r.kernel.org>
Subject: Re: [PATCH] drivers/net/wan/lapbether: Use needed_headroom instead of hard_header_len

Hi Cong Wang,

I'm wishing to change a driver from using "hard_header_len" to using
"needed_headroom" to declare its needed headroom. I submitted a patch
and it is decided it needs to be reviewed. I see you participated in
"hard_header_len vs needed_headroom" discussions in the past. Can you
help me review this patch? Thanks!

The patch is at:
http://patchwork.ozlabs.org/project/netdev/patch/20200726110524.151957-1-xie.he.0141@gmail.com/

In my understanding, hard_header_len should be the length of the header
created by dev_hard_header. Any additional headroom needed should be
declared in needed_headroom instead of hard_header_len. I came to this
conclusion by examining the logic of net/packet/af_packet.c:packet_snd.

What do you think?

Thanks!