Re: [Qemu-block] [PATCH 4/5] block/qcow2-bitmap: Allow resizes with persistent bitmaps

[Eric Blake]

On 3/6/19 9:33 AM, Vladimir Sementsov-Ogievskiy wrote:

>> +    /* Flush bitmaps */
>> +    if (s->nb_bitmaps) {
>> +        Error *local_err = NULL;
>> +
>> +        /* Usually, bitmaps get resized after this call.
>> +         * Force it earlier so we can make the metadata consistent. */
>> +        bdrv_dirty_bitmap_truncate(bs, offset);
>> +        qcow2_flush_persistent_dirty_bitmaps(bs, &local_err);
>> +        if (local_err) {
>> +            ret = -EINVAL;
>> +            goto fail;
>> +        }
>> +    }
> 
> Why to flush after resize? Bitmaps will be IN_USE in the image anyway...
> 
> Could we implement resize without flush first,  it would be one patch + test? 
> And then consider
> flushing in separate?

What happens with migration if we don't flush the new size to disk, so
the on-disk format has a different size than the in-memory version?

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

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