linux-kernel - Re: [PATCH v1 4/6] vfio-pci/zdev: Setup a zpci memory region for error information

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Message-ID: <f18e339f-0eb6-4270-9107-58bb70ef0d08@linux.ibm.com>
Date: Wed, 13 Aug 2025 14:25:59 -0700
From: Farhan Ali <alifm@...ux.ibm.com>
To: Alex Williamson <alex.williamson@...hat.com>
Cc: linux-s390@...r.kernel.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, schnelle@...ux.ibm.com,
        mjrosato@...ux.ibm.com
Subject: Re: [PATCH v1 4/6] vfio-pci/zdev: Setup a zpci memory region for
 error information


On 8/13/2025 1:30 PM, Alex Williamson wrote:
> On Wed, 13 Aug 2025 10:08:18 -0700
> Farhan Ali <alifm@...ux.ibm.com> wrote:
>> diff --git a/include/uapi/linux/vfio_zdev.h b/include/uapi/linux/vfio_zdev.h
>> index 77f2aff1f27e..bcd06f334a42 100644
>> --- a/include/uapi/linux/vfio_zdev.h
>> +++ b/include/uapi/linux/vfio_zdev.h
>> @@ -82,4 +82,9 @@ struct vfio_device_info_cap_zpci_pfip {
>>   	__u8 pfip[];
>>   };
>>   
>> +struct vfio_device_zpci_err_region {
>> +	__u16 pec;
>> +	int pending_errors;
>> +};
>> +
>>   #endif
> If this is uapi it would hopefully include some description, but if
> this is the extent of what can be read from the device specific region,
> why not just return it via a DEVICE_FEATURE ioctl?  Thanks,
>
> Alex
>
Yes, will add more details about the uapi. My thinking was based on how 
we expose some other vfio device information on s390x, such as SCHIB for 
vfio-ccw device.

I didn't think about the DEVICE_FEATURE ioctl. But looking into it, it 
looks like we would have to define a device feature (for eg: 
VFIO_DEVICE_FEATURE_ZPCI_ERROR), and expose this information via 
GET_FEATURE? If the preference is to use the DEVICE_FEATURE ioctl I can 
try that. Curious, any specific reason you prefer the DEVICE_FEATURE 
ioctl to the memory region?

Thanks
Farhan