Date: Tue, 12 Oct 2004 18:57:40 +0300 From: Giorgos Keramidas <keramida@freebsd.org> To: Dag-Erling Sm?rgrav <des@des.no> Cc: freebsd-arch@freebsd.org Subject: Re: mbuf w/o pkthdr? Message-ID: <20041012155740.GA1648@orion.daedalusnetworks.priv> In-Reply-To: <xzpy8ict0cy.fsf@dwp.des.no> References: <Pine.LNX.4.60.0410121115430.30953@athena> <xzpy8ict0cy.fsf@dwp.des.no>
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On 2004-10-12 17:36, Dag-Erling Sm?rgrav <des@des.no> wrote: > Sam <sah@softcardsystems.com> writes: > > Are all packets supposed to have the M_PKTHDR flag? Why? > > IIRC, M_PKTHDR indicates the first mbuf in a chain when a packet is > split across multiple mbufs. This usually only happens for outgoing > packets, where protocol headers are constructed in separate mbufs > which are prepended to the chain as the packet moves down the stack. AFAIK, all the packets have an M_PKTHDR in the first mbuf of their chain. The presence of an M_PKTHDR flag only means that the beginning of the mbuf contains a (struct pkthdr) before the packet payload. This is not related to the splitting of packets to multiple mbufs or not, though. A small packet might have an M_PKTHDR but still fit in a single mbuf if its payload packet (including protocol headers and data) is less than MHLEN bytes.
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