Re: [PATCH] hw/pci/pcie: Forbid hot-plug via QMP if it's disabled on the slot

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

On Wed, Apr 08, 2020 at 12:51:20PM +0200, Igor Mammedov wrote:
> On Tue,  7 Apr 2020 16:50:17 +0200
> Julia Suvorova <jusual@redhat.com> wrote:
> 
> > Raise an error when trying to hot-plug/unplug a device through QMP to a device
> > with disabled hot-plug capability. This makes the device behaviour more
> > consistent and provides an explanation of the failure in the case of
> > asynchronous unplug.
> 
> it applies to hotplug in general (i.e. not only QMP)
> 
> > 
> > Signed-off-by: Julia Suvorova <jusual@redhat.com>
> > ---
> >  hw/pci/pcie.c | 24 +++++++++++++++++++++---
> >  1 file changed, 21 insertions(+), 3 deletions(-)
> > 
> > diff --git a/hw/pci/pcie.c b/hw/pci/pcie.c
> > index 0eb3a2a5d2..e9798caa8a 100644
> > --- a/hw/pci/pcie.c
> > +++ b/hw/pci/pcie.c
> > @@ -415,6 +415,7 @@ void pcie_cap_slot_plug_cb(HotplugHandler *hotplug_dev, DeviceState *dev,
> >  {
> >      PCIDevice *hotplug_pdev = PCI_DEVICE(hotplug_dev);
> >      uint8_t *exp_cap = hotplug_pdev->config + hotplug_pdev->exp.exp_cap;
> > +    uint32_t sltcap = pci_get_word(exp_cap + PCI_EXP_SLTCAP);
> >      PCIDevice *pci_dev = PCI_DEVICE(dev);
> >  
> >      /* Don't send event when device is enabled during qemu machine creation:
> > @@ -430,6 +431,13 @@ void pcie_cap_slot_plug_cb(HotplugHandler *hotplug_dev, DeviceState *dev,
> >          return;
> >      }
> >  
> > +    /* Hot-plug is disabled on the slot */
> > +    if ((sltcap & PCI_EXP_SLTCAP_HPC) == 0) {
> > +        error_setg(errp, "Device '%s' does not support hot-plug",
> > +                         DEVICE(hotplug_dev)->id);
> plug and unplug_req are synchronous. so one can skip on "Device '%s'",
> user will get this error message as response to device_add/del command.
> 
> and more exactly it's concrete slot that does not support hotplug, how about
> "slot doesn't support ..." or just "hotlpug is not supported"

Well device name is useful here, while these commands are synchronous
others aren't so log parsing might not be synchronous.

I do think we should mention slot since that's the reason
hotplug failed:
    "Device '%s' hot-plug failed: unsupported by slot"

> > +        return;
> > +    }
> > +
> >      /* To enable multifunction hot-plug, we just ensure the function
> >       * 0 added last. When function 0 is added, we set the sltsta and
> >       * inform OS via event notification.
> > @@ -464,14 +472,24 @@ static void pcie_unplug_device(PCIBus *bus, PCIDevice *dev, void *opaque)
> >      object_unparent(OBJECT(dev));
> >  }
> >  
> > -void pcie_cap_slot_unplug_request_cb(HotplugHandler *hotplug_dev,
> > +void pcie_cap_slot_unplug_request_cb(HotplugHandler *hotplug_handler,
> >                                       DeviceState *dev, Error **errp)
> >  {
> >      Error *local_err = NULL;
> >      PCIDevice *pci_dev = PCI_DEVICE(dev);
> >      PCIBus *bus = pci_get_bus(pci_dev);
> > +    PCIDevice *hotplug_dev = PCI_DEVICE(hotplug_handler);
> > +    uint8_t *exp_cap = hotplug_dev->config + hotplug_dev->exp.exp_cap;
> > +    uint32_t sltcap = pci_get_word(exp_cap + PCI_EXP_SLTCAP);
> > +
> > +    /* Hot-unplug is disabled on the slot */
> > +    if ((sltcap & PCI_EXP_SLTCAP_HPC) == 0) {
> > +        error_setg(errp, "Device '%s' does not support hot-unplug",
> > +                         DEVICE(hotplug_dev)->id);
> > +        return;

Here too let's mention slot since that's the reason
hotplug failed:
    "Device '%s' hot-unplug failed: unsupported by slot"

?

> > +    }
> >  
> > -    pcie_cap_slot_plug_common(PCI_DEVICE(hotplug_dev), dev, &local_err);
> > +    pcie_cap_slot_plug_common(hotplug_dev, dev, &local_err);
> >      if (local_err) {
> >          error_propagate(errp, local_err);
> >          return;
> > @@ -490,7 +508,7 @@ void pcie_cap_slot_unplug_request_cb(HotplugHandler *hotplug_dev,
> >          return;
> >      }
> >  
> > -    pcie_cap_slot_push_attention_button(PCI_DEVICE(hotplug_dev));
> > +    pcie_cap_slot_push_attention_button(hotplug_dev);
> >  }
> >  
> >  /* pci express slot for pci express root/downstream port