Yamamoto-san,

Catching up a little further, I saw Jason's comments. I think Jason
and I are saying the same thing for the same reasons.

In message <56B83498-0B68-11D9-AD6D-000A957650EC@shagadelic.org>,
Jason Thorpe writes:
>
>--Apple-Mail-13--690926227
[...]

>> although i prefer M_EXT_READONLY because the most of mbufs are R/W,
>> M_EXT_RW is also ok for me.
>
>I suggested the "explicitly mark it RW" because the "implicit RO" 
>behavior has been around for a fairly long time, and there is external 
>code that depends on it, almost certainly.

Yes, except s/almost//. I also like the idea of an explicit writable flag.

Either way, the macros in sys/netipsec (at least, possibly elsewhere:
maybe netinet/ip_compat.h?) should be updated to match, if required.