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From: "Sam Leffler" <sam@errno.com>
To: "Julian Elischer" <julian@elischer.org>
Cc: <freebsd-arch@FreeBSD.ORG>, <freebsd-net@FreeBSD.ORG>
References: <Pine.BSF.4.21.0210071613260.34884-100000@InterJet.elischer.org>
Subject: Re: CFR: m_tag patch
Date: Mon, 7 Oct 2002 17:06:25 -0700
Organization: Errno Consulting
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> On Mon, 7 Oct 2002, Sam Leffler wrote:
> >
> > 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?

    Sam



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