netdev - Re: [net-next PATCH 2/5] ethernet/intel: Use eth_skb

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <1416974473.29427.49.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Tue, 25 Nov 2014 20:01:13 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	alexander.duyck@...il.com, alexander.h.duyck@...hat.com,
	netdev@...r.kernel.org, jeffrey.t.kirsher@...el.com
Subject: Re: [net-next PATCH 2/5] ethernet/intel: Use eth_skb_pad helper

On Tue, 2014-11-25 at 22:19 -0500, David Miller wrote:
> From: Eric Dumazet <eric.dumazet@...il.com>
> Date: Tue, 25 Nov 2014 17:43:05 -0800
> 
> > I believe I finally have an idea why we had various + 15 in skb
> > allocations in TCP stack !
> 
> It was so that you could do one level of tunneling with "for
> free".  Or that is my recollection.
> 
> Those + 15 existed way before any of these padto() calls even
> existed.


Well, tunneling is added in front of the packet. Thats why we use
MAX_TCP_HEADER.

The +15 is in fact because TCP stack wanted to make sure the eventual
padding (needing tailroom, not headroom) was possible...

Note that ack packets never used the +15, but other packets did.


--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html