Re: [Qemu-devel] [PATCH 1/2] parallels: create parallels_inactivate() callback of block driver state

[Stefan Hajnoczi]

On Wed, Apr 05, 2017 at 06:12:05PM +0300, Denis V. Lunev wrote:
> We should avoid to image file at migration end when BDRV_O_INACTIVE

s/avoid to image/avoid writing to the image/ ?

> is set on the block driver state. All modifications should be done
> in advance, i.e. in bdrv_inactivate.
> 
> The patch also adds final bdrv_flush() to be sure that changes have
> reached disk finally before other side will access the image.

If migration fails/cancels on the source after .bdrv_inactivate() we
need to return to the "activated" state.  .bdrv_invalidate_cache() will
be called so I think it needs to be implemented by parallels to set
s->header->inuse again if BDRV_O_RDWR.

.bdrv_invalidate_cache() is also called on the destination at live
migration handover.  That's okay - it makes sense for the destination to
set the inuse field on success.

> -static void parallels_close(BlockDriverState *bs)
> +static int parallels_inactivate(BlockDriverState *bs)
>  {
> +    int err;
>      BDRVParallelsState *s = bs->opaque;
>  
> -    if (bs->open_flags & BDRV_O_RDWR) {
> -        s->header->inuse = 0;
> -        parallels_update_header(bs);
> +    if (!(bs->open_flags & BDRV_O_RDWR)) {
> +        return 0;
> +    }
> +
> +    s->header->inuse = 0;
> +    err = parallels_update_header(bs);
> +    if (err < 0) {

Should we set s->header->inuse again in all error paths in case
something calls parallels_hupdate_header() again later?

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