Re: [PATCH 04/21] qdev: allow setting drive property for realized device

[Max Reitz]

On 17.05.21 08:44, Vladimir Sementsov-Ogievskiy wrote:
> We need an ability to insert filters above top block node, attached to
> block device. It can't be achieved with blockdev-reopen command. So, we
> want do it with help of qom-set.
>
> Intended usage:
>
> 1. blockdev-add, creating the filter, which child is at top node A,
>     attached to some guest block device.

Is a “not” missing here, i.e. “not attached to any guest block device”? 
 I would have thought one would create a filtered tree that is not in 
use by any frontend, so that the filter need not take any permissions.

> 2. qom-set, to change bs attached to root blk from original node to
>     newly create filter.
>
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
>   hw/core/qdev-properties-system.c | 30 ++++++++++++++++++++++--------
>   1 file changed, 22 insertions(+), 8 deletions(-)

Looks good, just one question: (well, two, one was above)

> diff --git a/hw/core/qdev-properties-system.c b/hw/core/qdev-properties-system.c
> index 2760c21f11..7d97562654 100644
> --- a/hw/core/qdev-properties-system.c
> +++ b/hw/core/qdev-properties-system.c

[...]

> @@ -196,6 +209,7 @@ static void release_drive(Object *obj, const char *name, 
> void *opaque)
>   const PropertyInfo qdev_prop_drive = {
>       .name  = "str",
>       .description = "Node name or ID of a block device to use as a backend",
> +    .realized_set_allowed = true,
>       .get   = get_drive,
>       .set   = set_drive,
>       .release = release_drive,

Why not for qdev_prop_drive_iothread?

Max