Subject: Pseudo-disk driver
To: None <>
From: der Mouse <mouse@Rodents.Montreal.QC.CA>
List: tech-kern
Date: 10/30/2001 21:47:19
It seems to me that this is on-topic with the recent discussion about
making vnd capable of encryption.

I've built a pseudo-disk driver.  With suitable userland code, it could
in principle replace ccd, raid, vnd, encrypting vnd, just about any
software disk layer.  Of course, I don't recommend it as a replacement
for any of those, if only because it is far less performant than an
entirely in-kernel driver - but it could be useful for knocking
together experimental setups.  Or for things like the need that
prompted me to write it. :-)

That need is that I have a disk that appears to have an alpha
filesystem on it, and sparc fsck is unhappy with it.  ISTR having
trouble moving filesystems between machines of differing word sizes
before, so I wanted to run the alpha fsck on it - but actually
connecting it to the alpha would be inconvenient.

With the pseudo-disk in the alpha kernel, I just throw in userland
programs that know how to shovel bits over the network, and I _can_ run
the alpha fsck over the disk even when it is connected to a sparc.
(Well, I will be able to.  My alpha is still kernel-building - I didn't
develop the code there, and it's a NoName, no speed demon.)

As anyone who follows what I say here closely can probably guess, it's
for 1.4T.  Because of that, I wouldn't even mention it, except that I
do still see people saying they're running 1.4 variants, so it may be
of some use to someone.  (I've got a similar driver for tapes, which I
used at one point to let backup software think it was talking to a tape
drive when it was really talking to a disk file.)

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