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Date:      Mon, 20 Mar 2000 19:12:22 +0100
From:      Poul-Henning Kamp <phk@critter.freebsd.dk>
To:        Matthew Dillon <dillon@apollo.backplane.com>
Cc:        current@FreeBSD.ORG
Subject:   Re: patches for test / review 
Message-ID:  <19790.953575942@critter.freebsd.dk>
In-Reply-To: Your message of "Mon, 20 Mar 2000 09:36:22 PST." <200003201736.JAA70124@apollo.backplane.com> 

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In message <200003201736.JAA70124@apollo.backplane.com>, Matthew Dillon writes:

>    I think so.  I can give -current a quick synopsis of the plan but I've
>    probably forgotten some of the bits (note: the points below are not
>    in any particular order):

Thanks for the sketch.  It sounds really good.

Is it your intention that drivers which cannot work from the b_pages[]
array will call to map them into VM, or will a flag on the driver/dev_t/
whatever tell the generic code that it should be mapped before calling
the driver ?

What about unaligned raw transfers, say a raw CD read of 2352 bytes
from userland ?  I pressume we will need an offset into the first 
page for that ?

One thing I would like to see is for the buffers to know how to
write themselves.  There is nothing which mandates that a buffer
be backed by a disk-like device, and there are uses for buffers
which aren't.

Being able to say bp->bop_write(bp) rather than bwrite(bp) would
allow that flexibility.  Kirk already introduced a bio_ops[] but
made it global for now, that should be per buffer and have all the
bufferops in it, (except for the onces which instantiate the buffer).

If we had this, pseudo filesystems like DEVFS could use UFS for
much of their naming management.  This is currently impossible.

--
Poul-Henning Kamp             FreeBSD coreteam member
phk@FreeBSD.ORG               "Real hackers run -current on their laptop."
FreeBSD -- It will take a long time before progress goes too far!


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