Re: [Qemu-devel] [PATCH] pci: fixed mismatch of error-handling between pci_qdev_init() and qdev

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Nov 06, 2014 at 11:26:01AM +0900, SeokYeon Hwang wrote:
> 
> 
> > -----Original Message-----
> > From: Paolo Bonzini [mailto:paolo.bonzini@gmail.com] On Behalf Of Paolo
> > Bonzini
> > Sent: Wednesday, November 05, 2014 11:55 PM
> > To: Michael S. Tsirkin
> > Cc: Markus Armbruster; SeokYeon Hwang; qemu-devel@nongnu.org
> > Subject: Re: [Qemu-devel] [PATCH] pci: fixed mismatch of error-handling
> > between pci_qdev_init() and qdev
> > 
> > 
> > 
> > On 05/11/2014 14:28, Michael S. Tsirkin wrote:
> > > > I think bypassing the question by converting to realize makes the
> > > > most sense...
> > >
> > > I'm fine with doing that but Markus's patches wouldn't yet have solved
> > > the problem by themselves since init is still around, right?
> > >
> > > This probably means fixing this bug can't justify merging the realize
> > > patchset after freeze.
> > 
> > Yes, I agree.  I meant that the API is not very well defined.  I would
> > handle everything else on a case-by-case basis, by reviewing each init
> > function that is converted to realize.
> > 
> > Since the patch was for an out-of-tree device, it can wait for 2.3 anyway.
> > 
> > Paolo
> 
> I cannot fully understand your conversation.
> But, I think this patch is still worth before all 'init()' convert to
> 'realize()'.
> Moreover, It has no side effect at all.
> 
> Thanks.
> 

The root cause is API misuse: functions that return int
should return a negative code on failure, either 0 or >= 0 on success.
In rare cases, we use int as bool, so 0 on failure, 1 on success.

Your device returned 1 on failure, this broke things.
So don't do this then :)

The question would be: are there existing devices that return a positive
return code on init. If there are, it's a bug, but the best fix might be
your patch - easier that fixing many devices.

If there aren't, the patch isn't needed.

-- 
MST