Re: [Qemu-devel] [PATCHv7 5/6] fw_cfg: move qdev_init_nofail() from fw_cfg_init1() to callers

[Igor Mammedov]

On Fri, 7 Jul 2017 12:09:56 -0300
Eduardo Habkost <address@hidden> wrote:

> On Fri, Jul 07, 2017 at 04:58:17PM +0200, Igor Mammedov wrote:
> > On Fri, 7 Jul 2017 10:13:00 -0300
> > "Eduardo Habkost" <address@hidden> wrote:
> [...]
> > > I don't disagree with adding the assert(), but it looks like
> > > making fw_cfg_find() return NULL if there are multiple devices
> > > can be useful for realize.
> > > 
> > > In this case, it looks like Mark is relying on that in
> > > fw_cfg_common_realize(): if multiple devices are created,
> > > fw_cfg_find() will return NULL, and realize will fail.  This
> > > sounds like a more graceful way to handle multiple-device
> > > creation than crashing on fw_cfg_find().  This is the solution
> > > used by find_vmgenid_dev()/vmgenid_realize(), BTW.
> > 
> > I suspect that find_vmgenid_dev() works by luck as it could be
> > placed only as /machine/peripheral-anon/foo1 or /machine/peripheral/foo2
> >   object_resolve_partial_path() : machine
> >            object_resolve_partial_path() : peripheral-anon => foo1
> >            object_resolve_partial_path() : peripheral => foo2
> >            if (found /* foo2 */) {
> >                if (obj /* foo1 */) {
> >                    return NULL;
> 
> I don't think this is luck: object_resolve_partial_path() is
> explicitly documented to always return NULL if multiple matches
> are found, and I don't see any bug in its implementation that
> would break that functionality.

Maybe I'm reading it wrong, but consider following:
https://www.mail-archive.com/address@hidden/msg460692.html

it looks to me that using ambiguous argument is necessary for duplicate 
detection to work correctly.

>