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
