linux-kernel - RE: [EXT] [PATCH] mwifiex: set needed_headroom, not hard_header

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Date:   Thu, 5 Mar 2020 06:12:10 +0000
From:   Ganapathi Bhat <ganapathi.bhat@....com>
To:     Brian Norris <briannorris@...omium.org>
CC:     "linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Nishant Sarmukadam <nishants@...vell.com>,
        Amitkumar Karwar <amitkarwar@...il.com>,
        Xinming Hu <huxinming820@...il.com>,
        Arend Van Spriel <arend@...adcom.com>
Subject: RE: [EXT] [PATCH] mwifiex: set needed_headroom, not hard_header_len

Hi Brian,

> > > hard_header_len provides limitations for things like AF_PACKET, such
> > > that we don't allow transmitting packets smaller than this.
> >
> > OK; However, are we not supposed to mention hard_header_len also?
> 
> No, my understanding is that we do not need to bother with
> hard_header_len ourselves -- ether_setup() establishes the appropriate
> L2 header parameters. I think that's covered a little better below.

OK. I got you.
> 
> > > This is the essentially the same bug (and fix) that brcmfmac had,
> > > fixed in commit cb39288fd6bb ("brcmfmac: use ndev-
> >needed_headroom
> > > to reserve additional header space").
> >
> > OK; I read this commit:
> >
> > "... According to definition of LL_RESERVED_SPACE() and hard_header_len,
> we should use hard_header_len to reserve for L2 header, like ethernet
> header(ETH_HLEN) in our case and use needed_headroom for the additional
> headroom needed by hardware..."
> 
> Yeah, that's probably a little more verbose and accurate description, which is
> partly why I referred to that commit :)
> 
> > So, does it mean, hard_header_len is already considered by upper layer?
> 
> Right, it's set by ether_setup().

Yes, Thanks.

Acked-by: Ganapathi Bhat <ganapathi.gbhat@....com>

Regards,
Ganapathi