Re: [PATCH v2 00/21] blksnap - block devices snapshots module

[Hannes Reinecke]

On 1/17/23 22:04, Mike Snitzer wrote:
> On Fri, Dec 09 2022 at  9:23P -0500,
> Sergei Shtepa <sergei.shtepa@xxxxxxxxx> wrote:
>
> > Hi Jens. Hi Jonathan. Hi all.
> >
> > I am happy to offer a modified version of the Block Devices Snapshots
> > Module. It allows to create non-persistent snapshots of any block devices.
> > The main purpose of such snapshots is to provide backups of block devices.
> > See more in Documentation/block/blksnap.rst.
> >
> > The Block Device Filtering Mechanism is added to the block layer. This
> > allows to attach and detach block device filters to the block layer.
> > Filters allow to extend the functionality of the block layer.
> > See more in Documentation/block/blkfilter.rst.
> >
> > A tool, a library for working with blksnap and tests can be found at
> > www.github.com/veeam/blksnap.
> >
> > The first version was suggested at 13 June 2022. Many thanks to
> > Christoph Hellwig and Randy Dunlap for the review of that version.
> >
> > Changes:
> > - Forgotten "static" declarations have been added.
> > - The text of the comments has been corrected.
> > - It is possible to connect only one filter, since there are no others in
> >    upstream.
> > - Do not have additional locks for attach/detach filter.
> > - blksnap.h moved to include/uapi/.
> > - #pragma once and commented code removed.
> > - uuid_t removed from user API.
> > - Removed default values for module parameters from the configuration file.
> > - The debugging code for tracking memory leaks has been removed.
> > - Simplified Makefile.
> > - Optimized work with large memory buffers, CBT tables are now in virtual
> >    memory.
> > - The allocation code of minor numbers has been optimized.
> > - The implementation of the snapshot image block device has been
> >    simplified, now it is a bio-based block device.
> > - Removed initialization of global variables with null values.
> > - Only one bio is used to copy one chunk.
> > - Checked on ppc64le.
> >
> > The v1 version was suggested at 2 November 2022. Many thanks to Fabio
> > Fantoni for his for his participation in the "blksnap" project on github
> > and Jonathan Corbet for his article https://lwn.net/Articles/914031/.
> > Thanks to the impartial kernel test robot.
> >
> > Changes:
> > - Added documentation for Block Device Filtering Mechanism.
> > - Added documentation for Block Devices Snapshots Module (blksnap).
> > - The MAINTAINERS file has been updated.
> > - Optimized queue code for snapshot images.
> > - Fixed comments, log messages and code for better readability.
>
> [this reply got long...]
[ .. ]
> But you've already bypassed me, my hope is that Jens and Christoph
> agree that we need this line of development to be in service to other
> areas of the Linux block subsystem and its drivers that were
> established for the purposes of remapping IO.  It cannot just be
> the subset needed to cement veeam's ability to use Linux for its
> purposes (but I completely understand that is the point of veeam's
> exercise).
That's why I proposed my topic at LSF/MM, precisely to figure out how to 
handle these issues.

Cheers,

Hannes