Re: [Qemu-block] block migration and dirty bitmap reset

[Peter Lieven]

Am 08.03.2018 um 10:01 schrieb Fam Zheng:
> On Thu, Mar 8, 2018 at 4:57 PM, Peter Lieven <address@hidden> wrote:
> > > Am 08.03.2018 um 02:28 schrieb Fam Zheng <address@hidden>:
> > >
> > > > On Wed, 03/07 09:06, Peter Lieven wrote:
> > > > Hi,
> > > >
> > > > while looking at the code I wonder if the blk_aio_preadv and the 
> > > > bdrv_reset_dirty_bitmap order must
> > > > be swapped in mig_save_device_bulk:
> > > >
> > > >     qemu_mutex_lock_iothread();
> > > >     aio_context_acquire(blk_get_aio_context(bmds->blk));
> > > >     blk->aiocb = blk_aio_preadv(bb, cur_sector * BDRV_SECTOR_SIZE, &blk->qiov,
> > > >                                 0, blk_mig_read_cb, blk);
> > > >
> > > >     bdrv_reset_dirty_bitmap(bmds->dirty_bitmap, cur_sector * BDRV_SECTOR_SIZE,
> > > >                             nr_sectors * BDRV_SECTOR_SIZE);
> > > >     aio_context_release(blk_get_aio_context(bmds->blk));
> > > >     qemu_mutex_unlock_iothread();
> > > >
> > > > In mig_save_device_dirty we first reset the dirty bitmap and read then which 
> > > > shoulds like
> > > > a better idea.
> > > Yes, that sounds right to me.
> > >
> > > Fam
> > You mean the order should be swapped in mig_save_device_bulk as well?
> Yeah, resetting the dirty bitmap before reading makes sure we don't
> miss any new data.

I wonder if this can really happen during blk_aio_preadv?
Anyway better safe than sorry. It at least will not hurt to swap the order.

Peter