Date: Fri, 7 Jun 2002 12:55:53 -0700 (PDT) From: Archie Cobbs <archie@dellroad.org> To: freebsd-net@freebsd.org Subject: m->m_pkthdr.header Message-ID: <200206071955.g57JtrJ65814@arch20m.dellroad.org>
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Hi,
I'd like to get rid of this mbuf field "m->m_pkthdr.header".
Here are my reasons:
- It's broken. Consider this code:
copy = m_copypacket(m);
m_freem(m);
Typically m->m_pkthdr.header points into the data area of 'm'.
So now copy->m_pkthdr.header points at the same data, which has
already been freed and possibly reused.
- It is an obscure thing most people don't know about and is
ripe for causing hard to find bugs.
- It's only used in two places, (a) for secret communication between
the oltr driver and if_ether.c, and (b) as a temporary variable
in ip_input.c:
$ find . -type f -print | xargs grep -w m_pkthdr.header
./contrib/dev/oltr/if_oltr.c: m0->m_pkthdr.header = (void *)th;
./netinet/if_ether.c: th = (struct iso88025_header *)m->m_pkthdr.header;
./netinet/ip_input.c: m->m_pkthdr.header = ip;
./netinet/ip_input.c:#define GETIP(m) ((struct ip*)((m)->m_pkthdr.header))
My proposal:
- Replace the obfuscating GETIP() macro in ip_input.c with a variable.
- Rejigger the oltr driver to pass its "secret" information using
an auxillary mbuf instead of m->m_pkthdr.header.
Any comments/objections?
Thanks,
-Archie
__________________________________________________________________________
Archie Cobbs * Packet Design * http://www.packetdesign.com
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