[Libguestfs] [PATCH nbdkit] filters: Add copy-on-write filter.

[Richard W.M. Jones]

On Sat, Jan 20, 2018 at 04:58:43PM +0000, Richard W.M. Jones wrote:
> Eric, you'll probably find the design "interesting" ...
> It does work, for me at least.

I should add that if the use of SEEK_DATA etc proves too
adventurous, it wouldn't be much trouble to modify this
to use a simple block bitmap.  With a 4K block size the
bitmap is 1/32768th of the size of the disk, so even a 1 TB
disk only needs a 32 MB bitmap which can comfortably be
kept in memory.

But it seemed a shame to do that when the operating system
is essentially maintaining equivalent state.

Rich.

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