Re: [Qemu-trivial] [PATCH] dma/i82374: avoid double creation of i82374 device

[Paolo Bonzini <pbonzini@redhat.com>]

----- Original Message -----
> From: "Eduardo Habkost" <ehabkost@redhat.com>
> To: "Paolo Bonzini" <pbonzini@redhat.com>
> Cc: "Eduardo Otubo" <otubo@redhat.com>, qemu-devel@nongnu.org, qemu-trivial@nongnu.org, "Michael Tokarev"
> <mjt@tls.msk.ru>, "Markus Armbruster" <armbru@redhat.com>, "Alexander Graf" <agraf@suse.de>
> Sent: Saturday, September 16, 2017 12:21:13 AM
> Subject: Re: [PATCH] dma/i82374: avoid double creation of i82374 device
> 
> On Fri, Sep 15, 2017 at 12:18:11PM +0200, Paolo Bonzini wrote:
> > On 15/09/2017 11:06, Eduardo Otubo wrote:
> > > QEMU fails when used with the following command line:
> > > 
> > >   ./ppc64-softmmu/qemu-system-ppc64 -S -machine 40p,accel=tcg -device
> > >   i82374
> > >   qemu-system-ppc64: hw/isa/isa-bus.c:110: isa_bus_dma: Assertion
> > >   `!bus->dma[0] && !bus->dma[1]' failed.
> > >   Aborted (core dumped)
> > > 
> > > The 40p machine type already creates the device i82374. If specified in
> > > the
> > > command line, it will try to create it again, hence generating the error.
> > > The
> > > function isa_bus_dma() isn't supposed to be called twice for the same
> > > bus. One
> > > way to avoid this problem is to set user_creatable=false.
> > > 
> > > A possible fix in a near future would be making
> > > isa_bus_dma()/DMA_init()/i82374_realize() return an error instead of
> > > asserting
> > > as well.
> > > 
> > > Signed-off-by: Eduardo Otubo <otubo@redhat.com>
> > > ---
> > >  hw/dma/i82374.c | 5 +++++
> > >  1 file changed, 5 insertions(+)
> > > 
> > > diff --git a/hw/dma/i82374.c b/hw/dma/i82374.c
> > > index 6c0f975df0..e76dea8dc7 100644
> > > --- a/hw/dma/i82374.c
> > > +++ b/hw/dma/i82374.c
> > > @@ -139,6 +139,11 @@ static void i82374_class_init(ObjectClass *klass,
> > > void *data)
> > >      dc->realize = i82374_realize;
> > >      dc->vmsd = &vmstate_i82374;
> > >      dc->props = i82374_properties;
> > > +    dc->user_creatable = false;
> > > +    /*
> > > +     * Reason: i82374_realize() crashes (assertion failure inside
> > > isa_bus_dma()
> > > +     *         if the device is instantiated twice.
> > > +     */
> > >  }
> > >  
> > >  static const TypeInfo i82374_info = {
> > > 
> > 
> > This breaks "make check", doesn't it?
> 
> Why would it?  I don't see any test code using -device i82374.
> (endianness-test uses -device i82378).

You're right, both Aurelien and I were confused.  If you want to
accept this patch it would be fine then, even if giving an error may
be preferrable.

Paolo