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

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Date:   Mon, 27 Jul 2020 23:59:28 -0700
From:   Xie He <xie.he.0141@...il.com>
To:     Brian Norris <briannorris@...omium.org>,
        Cong Wang <xiyou.wangcong@...il.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        LKML <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 Brian Norris,

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 submitted a similar
patch in the past. So I think you might be able to help review my patch.
Can you help review my patch? Thanks!

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

As you have noted in the commit message of your patch, hard_header_len
has special meaning in AF_PACKET so we need to use needed_headroom
instead when we just need to reserve some header space. I believe the
value of hard_header_len should be the same as the length of the header
created by dev_hard_header.