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

[Vladimir Sementsov-Ogievskiy]

17.05.2021 18:48, Max Reitz wrote:
> 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.

node A is attached.

So, we have [blk] --root->  [A}

And want to insert a filter between blk and A.

We do

1.

[filter] --file--\
                 v
[blk] --root-->  [A]

2.

[blk] --root--> [filer] --file--> [A]

> > 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?

Hmm, the only reason is that I missed that part of architecture around here, 
I'm new to qdev code. Will add with next version


--
Best regards,
Vladimir