Re: [uml-devel] uml-patch-2.4.20-7

[Jeff Dike <jdike@addtoit.com>]

nuno.silva@vgertech.com said:
> Can you give us a brief explanation on what this does? :) 

It's not useful at the moment.

It's to support the standalone COW driver when I get around to finishing it.
You will set up a COW file on the command line like
	cow0=/dev/ubd1,/dev/ubd0 ubd0=backing-file ubd1=cow-file

Since I can't break the existing
	ubdx=cow-file,backing-file
syntax, that will need to continue to be supported.

This causes a problem with ubd1=cow-file in the first example.  As the ubd
driver is currently written, this will cause ubd1 to be effectively
	ubd1=cow-file,backing-file
because it will read the backing file from the COW header.

With the standalone COW driver, this is undesirable.  We want ubd1 to not
be interpretted as a COW file since cow0 will be doing that.

So, the best thing I could think of was to make you specify ubd1 as
	ubd1d=cow-file
which says 'this is just blocks of data, even though it looks like a COW file'.

This is non-optimal since the common case in the long run (standalone COW)
should be easy and not require any special extra crap, but I don't see a
way of doing that without breaking everyone's scripts.

				Jeff



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