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From: John Baldwin <jhb@freebsd.org>
To: freebsd-hackers@freebsd.org
Subject: Re: Mbuf memory handling
Date: Wed, 6 Feb 2013 08:36:55 -0500
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 (bigwig.baldwin.cx); Wed, 06 Feb 2013 09:41:54 -0500 (EST)
Cc: Axel Fischer <afischer@marvell.com>, Lino Sanfilippo <lsanfil@marvell.com>,
 Markus Althoff <malthoff@marvell.com>
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On Wednesday, February 06, 2013 4:50:39 am Lino Sanfilippo wrote:
> 
> Hi all,
> 
> I want to implement a device driver for a NIC which stores received data into chunks within
> a page (>=4k) in host memory. One page shall be used for multiple packets and freed
> after all mbufs linked to that page have been processed. So I would like to know what is the recommended way
> to handle this in FreeBSD? Any hints are very appreciated.

I think you can get what you want by allocating M_JUMBOP mbuf clusters for
your receive buffers.  When you want to split out a packet, allocate a new
packet header mbuf and use m_split() to let it take over the rest of the 4k
buffer and pass the original mbuf up to if_input() as the new packet.  The
new mbufs you attach to the cluster via m_split() will all hold a reference
on the backing cluster and it won't be freed until all the mbufs are freed.

-- 
John Baldwin