From owner-freebsd-net  Tue Apr 25 17: 4:44 2000
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From: Archie Cobbs <archie@whistle.com>
Message-Id: <200004260003.RAA55104@bubba.whistle.com>
Subject: Re: Proposal for ethernet, bridging, netgraph
In-Reply-To: <20000425164027.A2553@waterspout.com> from "C. Stephen Gunn" at "Apr 25, 2000 04:40:27 pm"
To: csg@waterspout.com (C. Stephen Gunn)
Date: Tue, 25 Apr 2000 17:03:57 -0700 (PDT)
Cc: freebsd-net@freebsd.org
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C. Stephen Gunn writes:
> >   2. NFS requires that the IP packet be longword aligned (or something).
> >      If you start the mbuf with a 14-byte Ethernet header, then this
> >      is broken (?? is this still true ??)
> 
> Perhaps I misunderstand something here, but the packet-header should
> be long-since-gone by the time it gets to NFS.  If NFS needs the
> packet aligned, I'd assume that NFS takes care that monkey-business.

Well, the mbuf is aligned.. so if the IP header starts at mbuf +
14, then it's not aligned... and m_adj() won't help either.. but
I don't know whether this is still valid though.  However, a couple
of drivers take pains to handle this.

> >   3. Some code actually reads the header and the payload into
> >      different buffers. Putting them together, and then separating
> >      them again later would be slower than it is now.
> 
> I did a quick sampling of Ethernet devices in the kernel, and I
> couldn't find any that didn't call m_adj() right before ether_input().
> This was back in January, so I can't be sure now it was an exhaustive
> search.

See dev/ie/if_ie.c for an example..

-Archie

___________________________________________________________________________
Archie Cobbs   *   Whistle Communications, Inc.  *   http://www.whistle.com


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