Re: [PATCH] hw/pci/pcie: Move hot plug capability check to pre_plug callback

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

On Thu, Jun 04, 2020 at 12:57:55PM +0200, Igor Mammedov wrote:
> On Mon,  1 Jun 2020 18:29:34 +0200
> Julia Suvorova <jusual@redhat.com> wrote:
> 
> > Check for hot plug capability earlier to avoid removing devices attached
> > during the initialization process.
> > 
> > Run qemu with an unattached drive:
> >   -drive file=$FILE,if=none,id=drive0 \
> >   -device pcie-root-port,id=rp0,slot=3,bus=pcie.0,hotplug=off
> > Hotplug a block device:
> >   device_add virtio-blk-pci,id=blk0,drive=drive0,bus=rp0
> > If hotplug fails on plug_cb, drive0 will be deleted.
> > 
> > Signed-off-by: Julia Suvorova <jusual@redhat.com>
> > ---
> > Hard to say if it's a bug or generally acceptable behaviour, but seems like
> > hotplug_handler_plug should never fail.
> 
> _unplug shouldn't fail the rest are allowed to, but it's hard to unwind
> intialization cleanly to _plug stage so if it's possible to do checks
> at _pre_plug time (i.e. before device's realize() is called) we should do so.
> 
> Acked-by: Igor Mammedov <imammedo@redhat.com>


Makes sense. Julia could you repost with a tweaked commit log
and I'll apply. Thanks!


> > 
> >  hw/pci/pcie.c | 19 +++++++++++--------
> >  1 file changed, 11 insertions(+), 8 deletions(-)
> > 
> > diff --git a/hw/pci/pcie.c b/hw/pci/pcie.c
> > index f50e10b8fb..5b9c022d91 100644
> > --- a/hw/pci/pcie.c
> > +++ b/hw/pci/pcie.c
> > @@ -407,6 +407,17 @@ static void pcie_cap_slot_plug_common(PCIDevice *hotplug_dev, DeviceState *dev,
> >  void pcie_cap_slot_pre_plug_cb(HotplugHandler *hotplug_dev, DeviceState *dev,
> >                                 Error **errp)
> >  {
> > +    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);
> > +
> > +    /* Check if hot-plug is disabled on the slot */
> > +    if (dev->hotplugged && (sltcap & PCI_EXP_SLTCAP_HPC) == 0) {
> > +        error_setg(errp, "Hot-plug failed: unsupported by the port device '%s'",
> > +                         DEVICE(hotplug_pdev)->id);
> > +        return;
> > +    }
> > +
> >      pcie_cap_slot_plug_common(PCI_DEVICE(hotplug_dev), dev, errp);
> >  }
> >  
> > @@ -415,7 +426,6 @@ 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:
> > @@ -431,13 +441,6 @@ void pcie_cap_slot_plug_cb(HotplugHandler *hotplug_dev, DeviceState *dev,
> >          return;
> >      }
> >  
> > -    /* Check if hot-plug is disabled on the slot */
> > -    if ((sltcap & PCI_EXP_SLTCAP_HPC) == 0) {
> > -        error_setg(errp, "Hot-plug failed: unsupported by the port device '%s'",
> > -                         DEVICE(hotplug_pdev)->id);
> > -        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.