On Fri, Jun 07, 2002 at 12:55:53PM -0700, Archie Cobbs wrote: > 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);
Indeed, this is a bug in m_copypacket(). It should copy the data over, but again, admittedly, this is a very dangerous practise! Ideally, what ought to happen is that the copying over needs to be done by the code calling m_copypacket(), right after the m_copypacket() call but before the m_freem() call. The reason to do it from the caller code and not from m_copypacket() is that there is no reasonable way to determine, from m_copypacket(), whether or not one of our header/mbuf pointers points to a data inside the mbuf or whether it is safe to do the shallow pointer copy. > 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? None from here. :-) Just the standard pointer, which you probably already know: -CURRENT first, please. > Thanks, > -Archie > > __________________________________________________________________________ > Archie Cobbs * Packet Design * http://www.packetdesign.com Regards, -- Bosko Milekic [EMAIL PROTECTED] [EMAIL PROTECTED] To Unsubscribe: send mail to [EMAIL PROTECTED] with "unsubscribe freebsd-net" in the body of the message
