linux-kernel - Re: [PATCH v4 1/2] drivers/misc: sysgenid: add system generation id driver

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Date:   Tue, 2 Feb 2021 09:32:50 -0500
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Pavel Machek <pavel@....cz>
Cc:     Adrian Catangiu <acatan@...zon.com>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, qemu-devel@...gnu.org,
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Subject: Re: [PATCH v4 1/2] drivers/misc: sysgenid: add system generation id
 driver

On Wed, Jan 27, 2021 at 11:15:05PM +0100, Pavel Machek wrote:
> Hi!
> 
> > - Solution
> > 
> > The System Generation ID is a simple concept meant to alleviate the
> > issue by providing a monotonically increasing u32 counter that changes
> > each time the VM or container is restored from a snapshot.
> 
> I'd make it u64.
> 
> But as people explained, this has race problems that may be impossible
> to solve?

Well the read/write interface could be used in a safe way thinkably:

- application checks VM gen id
- application sends a transaction e.g. to  database
- application re-checks VM gen id
- if id changed, application checks the database for duplicate
  transactions

not sure how can the mmap interface be used safely.
Drop it for now?



> Best regards,
> 								Pavel
> 								
> -- 
> http://www.livejournal.com/~pavelmachek