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From: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-ID: <57615330.1050208@virtuozzo.com>
Date: Wed, 15 Jun 2016 16:08:00 +0300
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Subject: Re: [Qemu-devel] [PATCH 2/2] block: fix libvirt snapshot with
 existing bitmaps
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To: Eric Blake <eblake@redhat.com>, qemu-devel@nongnu.org
Cc: kwolf@redhat.com, den@openvz.org, mreitz@redhat.com

On 15.06.2016 00:33, Eric Blake wrote:
> On 06/14/2016 11:08 AM, Vladimir Sementsov-Ogievskiy wrote:
>> Fix the following bug:
>>
>>   # virsh start test
>>   Domain test started
>>
>>   #  virsh qemu-monitor-command test \
>>       '{"execute":"block-dirty-bitmap-add",\
>>        "arguments":{"node":"drive0","name":"ab"}}'
>>   {"return":{},"id":"libvirt-36"}'}'
>>
>>   # virsh snapshot-create test
>>   error: Unable to read from monitor: Connection reset by peer
>>
>> Actually, assert "assert(pos < hb->size)" in hbitmap_iter_init fires,
>> because qcow2_save_vmstate just writes to bs (not to bs->file->bs) after
>> the end of the drive.
>>
>> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
>> ---
>>   block/dirty-bitmap.c | 14 ++++++++++++++
>>   1 file changed, 14 insertions(+)
>>
>> diff --git a/block/dirty-bitmap.c b/block/dirty-bitmap.c
>> index 4902ca5..d28b49c 100644
>> --- a/block/dirty-bitmap.c
>> +++ b/block/dirty-bitmap.c
>> @@ -364,6 +364,20 @@ void bdrv_set_dirty(BlockDriverState *bs, int64_t cur_sector,
>>                       int nr_sectors)
>>   {
>>       BdrvDirtyBitmap *bitmap;
>> +    int64_t bitmap_size;
>> +
>> +    if (QLIST_EMPTY(&bs->dirty_bitmaps)) {
>> +        return;
>> +    }
>> +
>> +    bitmap_size = QLIST_FIRST(&bs->dirty_bitmaps)->size;
>> +
>> +    if (cur_sector >= bitmap_size) {
>> +        /* this may come from qcow2_save_vmstate */
>> +        return;
>> +    }
> Do we still need this patch after Kevin's work to fix vmstate to no
> longer go through the block layer?

I think not. If we are not going through block layer we are not touching 
dirty bitmaps.

>
> https://lists.gnu.org/archive/html/qemu-devel/2016-06/msg02832.html
>


-- 
Best regards,
Vladimir