From owner-freebsd-hackers  Fri Jun 26 07:06:51 1998
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To: Thomas David Rivers <rivers@dignus.com>
cc: hackers@FreeBSD.ORG
Subject: Re: Heads up: block devices to disappear! 
In-reply-to: Your message of "Wed, 24 Jun 1998 10:01:52 EDT."
             <199806241401.KAA04665@lakes.dignus.com> 
From: David Greenman <dg@root.com>
Reply-To: dg@root.com
Date: Fri, 26 Jun 1998 07:00:25 -0700
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>Terry Lambert writes:
>> had in no other fashion.  Let's meake sure that the block device interface
>> is not in the same [complex but useful - ed.] category before summarily 
>> executing it.
>
> In a similar context - I'd like to ask some simple questions.
>
> Can anyone clearly state why they were needed in UNIX at it's offset?
>
> Once that is understood - is it still the case, or has it been obviated
> in some way?
>
> I believe answers to these questions would be illuminating for the
> nervous amongst us (I count myself in the 'nervous' category on this one.)
>
> The reason I call for caution is simple - these have been with UNIX
> a long time... if they could have been simplified at the offset, why
> weren't they?  What's different now?
>
> I'm not saying it's a bad idea, I'd just like to understand what's
> changed from 20+ years ago...

   All caching in Unix used to be device-based and the block device was the
thing being cached (as opposed to the character device which is uncached).
Starting with 4.4BSD, the cache is file-based, making the main reason for
the existence of the block device obsolete.

-DG

David Greenman
Co-founder/Principal Architect, The FreeBSD Project

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