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SubjectRe: [PATCH 0/2] block layer filter and block device snapshot module
The 10/21/2020 16:31, Hannes Reinecke wrote:
> I do understand where you are coming from, but then we already have a
> dm-snap which does exactly what you want to achieve.
> Of course, that would require a reconfiguration of the storage stack on
> the machine, which is not always possible (or desired).

Yes, reconfiguring the storage stack on a machine is almost impossible.

>
> What I _could_ imagine would be a 'dm-intercept' thingie, which
> redirects the current submit_bio() function for any block device, and
> re-routes that to a linear device-mapper device pointing back to the
> original block device.
>
> That way you could attach it to basically any block device, _and_ can
> use the existing device-mapper functionality to do fancy stuff once the
> submit_io() callback has been re-routed.
>
> And it also would help in other scenarios, too; with such a
> functionality we could seamlessly clone devices without having to move
> the whole setup to device-mapper first.

Hm...
Did I understand correctly that the filter itself can be left approximately
as it is, but the blk-snap module can be replaced with 'dm-intercept',
which would use the re-route mechanism from the dm?
I think I may be able to implement it, if you describe your idea in more
detail.


--
Sergei Shtepa
Veeam Software developer.

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