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Re: [PATCH RFC 12/19] vfio-user: probe remote device's BARs


From: John Johnson
Subject: Re: [PATCH RFC 12/19] vfio-user: probe remote device's BARs
Date: Tue, 20 Jul 2021 01:39:21 +0000


> On Jul 19, 2021, at 3:59 PM, Alex Williamson <alex.williamson@redhat.com> 
> wrote:
> 
> On Sun, 18 Jul 2021 23:27:51 -0700
> Elena Ufimtseva <elena.ufimtseva@oracle.com> wrote:
>> @@ -3442,6 +3448,22 @@ static void vfio_user_pci_realize(PCIDevice *pdev, 
>> Error **errp)
>>     /* QEMU can also add or extend BARs */
>>     memset(vdev->emulated_config_bits + PCI_BASE_ADDRESS_0, 0xff, 6 * 4);
>> 
>> +    /*
>> +     * Local QEMU overrides aren't allowed
>> +     * They must be done in the device process
>> +     */
>> +    if (pdev->cap_present & QEMU_PCI_CAP_MULTIFUNCTION) {
>> +        error_setg(errp, "Multi-function must be specified by device 
>> process");
>> +        goto error;
>> +    }
>> +    if (pdev->romfile) {
>> +        error_setg(errp, "Romfile must be specified by device process");
>> +        goto error;
>> +    }
> 
> For what reason?  PCI functions can operate completely independently,
> there could be different servers for different functions, a QEMU user
> may wish to apply a different option ROM image than provided by the
> server.  This all creates unnecessary incompatibilities.  Thanks,
> 

        The idea is to have all the device options specified on the remote
server, and have the vfio client just be a pass-through device.  I thought
having them specified in 2 places would cause more confusion.

                                                                JJ




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