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

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Message-ID: <20190509065527.GG24397@joy-OptiPlex-7040>
Date:   Thu, 9 May 2019 02:55:27 -0400
From:   Yan Zhao <yan.y.zhao@...el.com>
To:     Boris Fiuczynski <fiuczy@...ux.ibm.com>
Cc:     Alex Williamson <alex.williamson@...hat.com>,
        Halil Pasic <pasic@...ux.ibm.com>,
        Tony Krowiak <akrowiak@...ux.ibm.com>,
        Pierre Morel <pmorel@...ux.ibm.com>,
        "cjia@...dia.com" <cjia@...dia.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "aik@...abs.ru" <aik@...abs.ru>,
        "Zhengxiao.zx@...baba-inc.com" <Zhengxiao.zx@...baba-inc.com>,
        "shuangtai.tst@...baba-inc.com" <shuangtai.tst@...baba-inc.com>,
        "qemu-devel@...gnu.org" <qemu-devel@...gnu.org>,
        "kwankhede@...dia.com" <kwankhede@...dia.com>,
        "eauger@...hat.com" <eauger@...hat.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "eskultet@...hat.com" <eskultet@...hat.com>,
        "Yang, Ziye" <ziye.yang@...el.com>,
        "mlevitsk@...hat.com" <mlevitsk@...hat.com>,
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        "Tian, Kevin" <kevin.tian@...el.com>,
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        "intel-gvt-dev@...ts.freedesktop.org" 
        <intel-gvt-dev@...ts.freedesktop.org>,
        "Liu, Changpeng" <changpeng.liu@...el.com>,
        "cohuck@...hat.com" <cohuck@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Wang, Zhi A" <zhi.a.wang@...el.com>,
        "jonathan.davies@...anix.com" <jonathan.davies@...anix.com>,
        "He, Shaopeng" <shaopeng.he@...el.com>
Subject: Re: [libvirt] [PATCH v2 1/2] vfio/mdev: add version attribute for
 mdev device

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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