Re: [libvirt] [PATCH v2 1/2] vfio/mdev: add version attribute for mdev device

From: Yan Zhao <yan.y.zhao@intel.com>
To: Boris Fiuczynski <fiuczy@linux.ibm.com>
Cc: Alex Williamson <alex.williamson@redhat.com>,
	Halil Pasic <pasic@linux.ibm.com>,
	Tony Krowiak <akrowiak@linux.ibm.com>,
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Subject: Re: [libvirt] [PATCH v2 1/2] vfio/mdev: add version attribute for mdev device
Date: Thu, 9 May 2019 02:55:27 -0400	[thread overview]
Message-ID: <20190509065527.GG24397@joy-OptiPlex-7040> (raw)
In-Reply-To: <5eac912c-e753-b5f6-83a4-b646f991d858@linux.ibm.com>

On Wed, May 08, 2019 at 11:27:47PM +0800, Boris Fiuczynski wrote:
> On 5/8/19 11:22 PM, Alex Williamson wrote:
> >>> I thought there was a request to make this more specific to migration
> >>> by renaming it to something like migration_version.  Also, as an
> >>>   
> >> so this attribute may not only include a mdev device's parent device info and
> >> mdev type, but also include numeric software version of vendor specific
> >> migration code, right?
> > It's a vendor defined string, it should be considered opaque to the
> > user, the vendor can include whatever they feel is relevant.
> > 
> Would a vendor also be allowed to provide a string expressing required 
> features as well as containing backend resource requirements which need 
> to be compatible for a successful migration? Somehow a bit like a cpu 
> model... maybe even as json or xml...
> I am asking this with vfio-ap in mind. In that context checking 
> compatibility of two vfio-ap mdev devices is not as simple as checking 
> if version A is smaller or equal to version B.
>
I think so. vendor driver is allowed to put whatever content into the
migration_version string as long as it thinks it's necessary. 
vendor driver only needs ensure in the target mdev device, the write(2)
operation on its migration_version attribute would correctly fail or succeeed
based on the input string.

Thanks
Yan
> -- 
> Mit freundlichen Grüßen/Kind regards
>     Boris Fiuczynski
> 
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