Date: Fri, 11 Oct 2002 11:12:02 -0700 From: "Sam Leffler" <sam@errno.com> To: <jinmei@isl.rdc.toshiba.co.jp> Cc: "Julian Elischer" <julian@elischer.org>, <freebsd-arch@FreeBSD.ORG>, <freebsd-net@FreeBSD.ORG> Subject: Re: CFR: m_tag patch Message-ID: <080101c27151$b2e92a30$52557f42@errno.com> References: <Pine.BSF.4.21.0210071613260.34884-100000@InterJet.elischer.org> <18d301c26e5e$8b5c7a30$52557f42@errno.com> <y7vd6qhg0vj.wl@ocean.jinmei.org>
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> >>>>> On Mon, 7 Oct 2002 17:06:25 -0700,
> >>>>> "Sam Leffler" <sam@errno.com> said:
>
> >> > If you allocate tag id's using your 32-bit time scheme then the fixed
> > values
> >> > above would never be hit since they are all for impossible times and
so
> >> > there'd be no conflict.
> >>
> >> Just make them all IDs in a single "Legacy" API
> >>
>
> > Good idea; I see the way out. Try this:
>
> > struct m_tag {
> > SLIST_ENTRY(m_tag) m_tag_link; /* List of packet tags
*/
> > u_int16_t m_tag_id; /* Tag ID */
> > u_int16_t m_tag_len; /* Length of data */
> > u_int32_t m_tag_cookie; /* Module/ABI */
> > };
>
> > Then define the "Legacy ABI" to be zero (or whatever you want). Then
all
> > the m_tag_* routines that I specified work only for the Legacy ABI.
> > (Whether this is done with shims or whatever doesn't matter.) This
gives me
> > the compatiblity I want with openbsd and gives you the functionality you
> > need for netgraph. For new work we can specify users should avoid the
> > Legacy ABI.
>
> > Cost is basically 4 bytes per tag and an extra compare when walking the
> > tags. Happy?
>
> Sorry for interrupting, but please let me make it sure. Do you intend
> to hide the additional member from other modules than the m_tag
> internal? I'm afraid a story that (e.g.) some code fragments in the
> network layer directly refers to m_tag_cookie, which will break source
> level compatibility with other BSDs (when the code fragments are
> shared with others). As suz said before, we (KAME) are very much
> afraid of this kind of story.
>
The changes I'm proposing for KAME code make no references to m_tag_cookie.
Things should be clear when you have a patch to look at. I'm working on
getting that to you.
Sam
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