[Sheepdog] [PATCH 3/3] sheep: fix nr_copies in vdi.c

[Christoph Hellwig]

On Tue, May 01, 2012 at 02:00:53AM +0800, Liu Yuan wrote:
> I think it is good time for us to implement rather than keep clear away
> of diff-redundant feature. If you don't have time in hands, we(or other
> in Taobao) will go to hack it up.

While I previously though marking it reserved for now might be a good
idea looking at the qemu client suggests removing it is a bad idea, as
it looks at the nr_copies variable in the end, and is very unhappy if
it's not set.

So I think the plan for now is:

 a) fix the bug in vdi deletetion
 b) audit the I/O pathes to actually respect hdr.copies.  I think it
    only should be read for !SD_FLAG_CMD_IO_LOCAL so that there is
    one place to do it instead of multiple places.  I suspect adding
    a variant of get_nr_copies that also takes a header is the best
    way to go there.
 c) fix the recovery algorithm for it.