Re: [Qemu-block] [Qemu-devel] [PATCH v7 11/20] dirty-bitmap: Change bdrv_dirty_iter_next() to report byte offset

[Eric Blake]

On 09/13/2017 07:15 PM, John Snow wrote:
> 
> 
> On 09/12/2017 04:31 PM, Eric Blake wrote:
>> Thanks to recent cleanups, most callers were scaling a return value
>> of sectors into bytes (the exception, in qcow2-bitmap, will be
>> converted to byte-based iteration later).  Update the interface to
>> do the scaling internally instead.
>>
>> In qcow2-bitmap, the code was specifically checking for an error
>> to be -1; it is more robust to treat all negative values as an
>> error, but at the same time it is also easy enough to ensure we
>> return -1 (and not -512) on error.
>>
>> Signed-off-by: Eric Blake <address@hidden>
>>
> 
> This patch now smells like a bugfix and a separate incremental feature
> enhancement.

There is no bug without this patch; more of a fix to avoid a latent
regression from happening in further changes.  In v6, I (accidentally)
had bdrv_dirty_iter_next() temporarily returning -512 instead of -1 on
failure; changing the qcow2 code to treat all negatives instead of
precisely -1 as error is enough to avoid that regression, but so also is
fixing bdrv_dirty_iter_next() to always return -1 on failure.  This
patch does both, rather than either fix in isolation, but that means we
don't need a backport.

> 
> Do we need to backport the error-checking to a possible 2.10.1?
> 
> If no:
> 
> Reviewed-by: John Snow <address@hidden>
> 

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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