[Libguestfs] Libguestfs Rsync-in with delta transfer enabled

[Richard W.M. Jones]

On Sat, Jun 18, 2022 at 06:18:58PM +0530, Ajay Nemade wrote:
> Hi,
>
> I am exploring libguestfs rsync-in to copy the incremental changes
> to qcow2. I am following rsync example to use the rsync-in. As per
> the example, I am using rsync daemon and rysnc-in is working for
> me. But, If the changes are in the same file then the complete file
> is getting transferred.
>
> For example, if my file is of 100Mi then the first qcow2 is of
> approx 105Mi.  After the first qcow2, I am appending data of 20Mi
> and then creating the second qcow2 using the first qcow2 as a
> backing file. Here then the second qcow2 should have been around
> approx 22Mi but it's showing 125Mi in qemu-img info.
>
> From the above observation, I think the delta transfer algorithm is
> not getting used while doing rsync-in.
>
> Just out of curiosity, I tried adding arg --no-whole-file in this
> function but it's still not working.
>
> Can anyone please point me to how to enable the delta transfer
> algorithm? Is it already supported ? or Do I need to make changes in
> the code? If yes, then please let me know the places where I should
> add the changes.

I'm not sure I know the correct answer.

I guess you have already tried modifying this code:

https://github.com/libguestfs/libguestfs/blob/60e8ea0312d94860403c956f0f12d491743d3fdd/daemon/rsync.c#L49

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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