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

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Date:   Wed, 18 Jan 2023 11:51:23 +0100
From:   Hannes Reinecke <hare@...e.de>
To:     Mike Snitzer <snitzer@...hat.com>,
        Sergei Shtepa <sergei.shtepa@...am.com>
Cc:     axboe@...nel.dk, corbet@....net, linux-block@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 00/21] blksnap - block devices snapshots module

On 1/17/23 22:04, Mike Snitzer wrote:
> On Fri, Dec 09 2022 at  9:23P -0500,
> Sergei Shtepa <sergei.shtepa@...am.com> 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