Re: [PATCH v5 02/11] pci: add option for net failover

[Jens Freimann]

On Wed, Oct 23, 2019 at 12:06:48PM -0600, Alex Williamson wrote:
> On Wed, 23 Oct 2019 10:27:02 +0200
> Jens Freimann <address@hidden> wrote:
>
> > This patch adds a net_failover_pair_id property to PCIDev which is
> > used to link the primary device in a failover pair (the PCI dev) to
> > a standby (a virtio-net-pci) device.
> >
> > It only supports ethernet devices. Also currently it only supports
> > PCIe devices. QEMU will exit with an error message otherwise.
> >
> > Signed-off-by: Jens Freimann <address@hidden>
> > ---
> >  hw/pci/pci.c         | 17 +++++++++++++++++
> >  include/hw/pci/pci.h |  3 +++
> >  2 files changed, 20 insertions(+)
> >
> > diff --git a/hw/pci/pci.c b/hw/pci/pci.c
> > index aa05c2b9b2..fa9b5219f8 100644
> > --- a/hw/pci/pci.c
> > +++ b/hw/pci/pci.c
> > @@ -75,6 +75,8 @@ static Property pci_props[] = {
> >                      QEMU_PCIE_LNKSTA_DLLLA_BITNR, true),
> >      DEFINE_PROP_BIT("x-pcie-extcap-init", PCIDevice, cap_present,
> >                      QEMU_PCIE_EXTCAP_INIT_BITNR, true),
> > +    DEFINE_PROP_STRING("net_failover_pair_id", PCIDevice,
> > +            net_failover_pair_id),
>
> Nit, white space appears broken here.

I'll fix it.

> >      DEFINE_PROP_END_OF_LIST()
> >  };
> >
> > @@ -2077,6 +2079,7 @@ static void pci_qdev_realize(DeviceState *qdev, Error 
> > **errp)
> >      ObjectClass *klass = OBJECT_CLASS(pc);
> >      Error *local_err = NULL;
> >      bool is_default_rom;
> > +    uint16_t class_id;
> >
> >      /* initialize cap_present for pci_is_express() and pci_config_size(),
> >       * Note that hybrid PCIs are not set automatically and need to manage
> > @@ -2101,6 +2104,20 @@ static void pci_qdev_realize(DeviceState *qdev, Error 
> > **errp)
> >          }
> >      }
> >
> > +    if (pci_dev->net_failover_pair_id) {
> > +        if (!pci_is_express(pci_dev)) {
> > +            error_setg(errp, "failover device is not a PCIExpress device");
> > +            error_propagate(errp, local_err);
> > +            return;
> > +        }
>
> Did we decide we don't need to test that the device is also in a
> hotpluggable slot?  

Hmm, my reply to you was never sent. I thought the check for
qdev_device_add() was sufficient but you said that works only
after qdev_hotplug is set (after machine creation). I modified
the check to this:

   hide = should_hide_device(opts);                                                                      
                                                                                                         
   if ((hide || qdev_hotplug) && bus && !qbus_is_hotpluggable(bus)) {                                    
       error_setg(errp, QERR_BUS_NO_HOTPLUG, bus->name);                                                 
       return NULL;                                                                                      
   }                                                                                                     
                                                                                                         
   if (hide) {                                                                                           
       return NULL;                                                                                      
   }

This will make qemu fail when we have the device in the initial
configuration or when we hotplug it to a bus that doesn't support it.
I tested both with a device on pcie.0. Am I missing something? 

> Are there also multi-function considerations that
> should be prevented or documented?  For example, if a user tries to
> configure both the primary and failover NICs in the same slot, I assume
> bad things will happen.

 I would have expected that this is already checked in pci code, but
it is not. I tried it and when I put both devices into the same slot
they are both unplugged from the guest during boot but nothing else
happens. I don't know what triggers that unplug of the devices.

I'm not aware of any other problems regarding multi-function, which
doesn't mean there aren't any. 

> > +        class_id = pci_get_word(pci_dev->config + PCI_CLASS_DEVICE);
> > +        if (class_id != PCI_CLASS_NETWORK_ETHERNET) {
> > +            error_setg(errp, "failover device is not an Ethernet device");
> > +            error_propagate(errp, local_err);
> > +            return;
> > +        }
> > +    }
>
> Looks like cleanup is missing both both error cases, the option rom
> error path below this does a pci_qdev_unrealize() before returning so
> I'd assume we want the same here.  Thanks,

Thanks, I'll fix this too.

regards,
Jens