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

[Igor Mammedov <imammedo@redhat.com>]

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"

> +        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;
> +    }
>  
> -    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