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Date:      Sun, 12 Nov 2000 20:56:42 +0000
From:      David Malone <dwmalone@maths.tcd.ie>
To:        Bosko Milekic <bmilekic@dsuper.net>
Cc:        David Malone <dwmalone@maths.tcd.ie>, iedowse@maths.tcd.ie, freebsd-net@freebsd.org
Subject:   Re: M_RDONLY: review & comment 
Message-ID:   <200011122056.aa55963@salmon.maths.tcd.ie>
In-Reply-To: Your message of "Sun, 12 Nov 2000 11:25:38 EST." <Pine.BSF.4.21.0011121119030.11341-100000@jehovah.technokratis.com> 

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> 	Not necessarily. If you'll notice, I changed the type for if_ti,
>   if_wb, etc. to have only ONE type, EXT_NET_DRV. The only real important
>   type is EXT_CLUSTER, because that's the one we always check to see if
>   it's "this one, or all the others." The others are there mainly for
>   debugging purposes.

Ahh - OK - I missed that. It still seems possible that it might be
better to just have a M_ISCLUSTER flag instead.

> > The other option I thought of is to use a char *. You could point
> > to a static string describing the type of external storage.
[snip]
> 	There are flaws with this. One is that there's no way to know ahead
>   of time what type has what address associated to it.

As you point out, we really only need to test for clusters and it
would be easy enough to export the address of this and have the
linker do the work. Strings would be more valueable while debugging,
but given that you're the person most likely to be debugging the
mbuf code... ;-)

>   I think what we
>   should do is maybe add EXT_MOD_TYPE and all the modules adding their own
>   ext_buf's that are _not_ network drivers can use that. Seems much simpler
>   to me. Note that this is unlike major/minor numbers in that each type
>   does not have to be unique.

Sounds reasonable, but again raises the question of why do we have
the type field anyway. (Just while I'm thinking of it, I wonder if
it is worth implimenting a 8K jumbo cluster type which any Gb/s
ethernet driver could use? I guess we should ask Bill Paul and Matt
Jacob if they think it would be useful.)

> 	Note that I will change the short ext_type to an int. It's typically
>   faster on the alpha and it doesn't cost us anything.

Cool - I guess we have tons of space left at the end of mbufs with
external storage?

	David.


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