Re: [PATCH 0/2] block/raw: implemented persistent dirty bitmap and ability to dump bitmap content via qapi

[Patrik Janoušek]

Hello, thank you for the quick reply.

On 3/22/21 9:29 AM, Vladimir Sementsov-Ogievskiy wrote:

> Hi
>       Patrik!
>       
>       
>       20.03.2021 12:32, Patrik Janoušek wrote:
>       
> > Currently, QEMU doesn't support persistent
> >         dirty bitmaps for raw format
> >         
> >       
>       
>       That's right, we don't have such feature now.
>       
>       
> > and also dirty bitmaps are for internal
> >         use only, and cannot be accessed
> >         
> >         using third-party applications.
> >         
> >       
>       
>       And that's is not. Bitmaps are accessible through bitmap QMP API
>       
>       
>         block-dirty-bitmap-{add,remove,clear,merge}
>       
>     
    I know about these commands, but they're useless to me without
    providing access to the content of bitmap.
>       
>       And to retrieve the context of dirty bitmap you can export it
>       through NBD protocol (see bitmaps argument in nbd specific options
>       of block-export-add command)
>       
>     
    Ok, I'll look at it.
>       
> > These facts are very limiting
> >         
> >         in case someone would like to develop their own backup tool
> >         becaouse
> >         
> >         without access to the dirty bitmap it would be possible to
> >         implement
> >         
> >         only full backups.
> >         
> >       
>       
>       We do have external incremental backups, based on Qemu bitmap API.
>       But it depends of course on qcow2 persistent bitmaps feature.
>       
>     
    Yes, I know. And that's the problem. The point of my bachelor thesis
    is to implement a backup solution for the raw format.
>       
> > And without persistent dirty bitmaps, it
> >         wouldn't
> >         
> >         be possible to keep track of changed data after QEMU is
> >         restarted. And
> >         
> >         this is exactly what I do as a part of my bachelor thesis. I've
> >         
> >         developed a tool that is able to create incremental backups of
> >         drives
> >         
> >         in raw format that are LVM volumes (ability to create snapshot
> >         is
> >         
> >         required).
> >         
> >         
> >         Please keep in mind that this is my first submission to such a
> >         large
> >         
> >         project and also the first time when I send patch over the
> >         email.
> >         
> >         So I hope I did it correctly.
> >         
> >         
> >         Patrik Janoušek (2):
> >         
> >            block/raw: added support of persistent dirty bitmaps
> >         
> >            qapi: implementation of the block-dirty-bitmap-dump command
> >         
> >         
> >           block/meson.build               |   1 +
> >         
> >           block/monitor/bitmap-qmp-cmds.c |  61 ++++++++
> >         
> >           block/raw-format-bitmap.c       | 163 ++++++++++++++++++++
> >         
> >           block/raw-format.c              | 256
> >         ++++++++++++++++++++++++++++++--
> >         
> >           block/raw-format.h              |  50 +++++++
> >         
> >           qapi/block-core.json            |  64 +++++++-
> >         
> >           6 files changed, 583 insertions(+), 12 deletions(-)
> >         
> >           create mode 100644 block/raw-format-bitmap.c
> >         
> >           create mode 100644 block/raw-format.h
> >         
> >         
> >       
>       
>       
>

Patrik Janoušek

IČO: 09291849

	+420 724 123 897
	pj@patrikjanousek.cz