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From: Lino Sanfilippo <lsanfil@marvell.com>
To: Jacques Fourie <jacques.fourie@gmail.com>, John Baldwin <jhb@freebsd.org>
Date: Wed, 6 Feb 2013 11:41:32 -0800
Subject: RE: Mbuf memory handling
Thread-Topic: Mbuf memory handling
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Cc: Hackers freeBSD <freebsd-hackers@freebsd.org>,
 Axel Fischer <afischer@marvell.com>, Ralf Assmann <rassmann@marvell.com>,
 Markus Althoff <malthoff@marvell.com>
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John, Jacques,

thank you very much for your help. An mbuf cluster seems to be the right di=
rection.
So I would have to do something like

mbuf =3D m_getjcl(how, MT_DATA, M_PKTHDR, MJUMPAGESIZE);
left_for_next_rcv =3D m_split(mbuf, chunksize);
if_input(ifp, mbuf);

right?

>I agree that read-only buffers may be ok in this case but would like to po=
int out that the M_WRITABLE() macro will evaluate to 0 if the refcount on t=
he cluster is >1

The fact that the resulting mbufs returned by m_split() are not writeable a=
ny more is indeed a problem:
What I would like to do is keep the 'left_for_next_rcv' mbuf until the next=
 packet arrives and
then fill it with the next packets data only up to 'chunksize', split it ag=
ain to pass the new mbuf to
the protocol stack and so on until 'left_for_next_rcv' becomes too small to=
 be splitted further.
Only then I would want to allocate a new "fresh" jumbo sized mbuf. Is it po=
ssible to
realize this with cluster mbufs?

Thx,
Lino