Re: [Qemu-devel] [PATCH 2/2] block: fix libvirt snapshot with existing bitmaps

[Max Reitz <mreitz@redhat.com>]

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On 15.06.2016 15:08, Vladimir Sementsov-Ogievskiy wrote:
> 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.

OK, I'll drop this patch, then. I'll keep the first patch, though,
because it seems useful anyway.

Max


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