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Re: [Qemu-devel] [PATCH v5 03/11] block: add basic backup support to blo


From: Paolo Bonzini
Subject: Re: [Qemu-devel] [PATCH v5 03/11] block: add basic backup support to block driver
Date: Wed, 19 Jun 2013 13:14:17 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130514 Thunderbird/17.0.6

Il 19/06/2013 12:50, Kevin Wolf ha scritto:
>> > +        /* Publish progress */
>> > +        job->sectors_read += n;
>> > +        job->common.offset += n * BDRV_SECTOR_SIZE;
> This is interesting, because the function is not only called by the
> background job, but also by write notifiers. So 'offset' in a literal
> sense doesn't make too much sense because we're not operating purely
> sequential.
> 
> The QAPI documentation describes 'offset' like this:
> 
> # @offset: the current progress value
> 
> If we take it as just that, I think we could actually consider this code
> correct, because it's a useful measure for the progress (each sector is
> copied only once, either by the job or by a notifier), even though it
> really has nothing to do with an offset into the image.

Yes, this is similar to what we do for mirroring.  I think it is a feature.

Paolo

> Maybe a comment would be appropriate.





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