>	For keeping IPsec decryption history and other information,
>	I would like to add one variable into mbuf header (M_PKTHDR),
>	like below.  this will let us attach extra mbuf chain to mbuf.

	list of things I've noticed:
	- freebsd (3.x and higher) has extra member, m->m_pkthdr.header for
	  ip4/tcp reassembly.
	- openbsd has extra member, m->m_pkthdr.tdbi for keeping IPsec
	  SPI lookup information.
	- netbsd has M_SETCTX() and M_GETCTX() macro, which seem to be used
	  by de* and pdq* only.  the use in de* and pdq* does not comflict
	  with, say, packet filters as the field will be reset to NULL by the
	  time the packet is put into input queue.
http://cvsweb.netbsd.org/bsdweb.cgi/syssrc/sys/sys/mbuf.h.diff?r1=1.30&r2=1.31

itojun