Re: [Qemu-devel] [PATCH v3 1/2] vfio/mdev: add migration_version attribute for mdev device

[Yan Zhao]

On Tue, May 28, 2019 at 04:53:32PM +0800, Cornelia Huck wrote:
> On Sun, 26 May 2019 23:43:42 -0400
> Yan Zhao <address@hidden> wrote:
> 
> > migration_version attribute is used to check migration compatibility
> > between two mdev device of the same mdev type.
> 
> s/device/devices/
>
yes... sorry and thanks :)

> > The key is that it's rw and its data is opaque to userspace.
> > 
> > Userspace reads migration_version of mdev device at source side and
> > writes the value to migration_version attribute of mdev device at target
> > side. It judges migration compatibility according to whether the read
> > and write operations succeed or fail.
> > 
> > As this attribute is under mdev_type node, userspace is able to know
> > whether two mdev devices are compatible before a mdev device is created.
> > 
> > userspace needs to check whether the two mdev devices are of the same
> > mdev type before checking the migration_version attribute. It also needs
> > to check device creation parameters if aggregation is supported in
> > future.
> > 
> >              __    userspace
> >               /\              \
> >              /                 \write
> >             / read              \
> >    ________/__________       ___\|/_____________
> >   | migration_version |     | migration_version |-->check migration
> >   ---------------------     ---------------------   compatibility
> >     mdev device A               mdev device B
> > 
> > Cc: Alex Williamson <address@hidden>
> > Cc: Erik Skultety <address@hidden>
> > Cc: "Dr. David Alan Gilbert" <address@hidden>
> > Cc: Cornelia Huck <address@hidden>
> > Cc: "Tian, Kevin" <address@hidden>
> > Cc: Zhenyu Wang <address@hidden>
> > Cc: "Wang, Zhi A" <address@hidden>
> > Cc: Neo Jia <address@hidden>
> > Cc: Kirti Wankhede <address@hidden>
> > Cc: Daniel P. Berrangé <address@hidden>
> > Cc: Christophe de Dinechin <address@hidden>
> > 
> > Signed-off-by: Yan Zhao <address@hidden>
> > 
> > ---
> > v3:
> > 1. renamed version to migration_version
> > (Christophe de Dinechin, Cornelia Huck, Alex Williamson)
> > 2. let errno to be freely defined by vendor driver
> > (Alex Williamson, Erik Skultety, Cornelia Huck, Dr. David Alan Gilbert)
> > 3. let checking mdev_type be prerequisite of migration compatibility
> > check. (Alex Williamson)
> > 4. reworded example usage section.
> > (most of this section came from Alex Williamson)
> > 5. reworded attribute intention section (Cornelia Huck)
> > 
> > v2:
> > 1. added detailed intent and usage
> > 2. made definition of version string completely private to vendor driver
> >    (Alex Williamson)
> > 3. abandoned changes to sample mdev drivers (Alex Williamson)
> > 4. mandatory --> optional (Cornelia Huck)
> > 5. added description for errno (Cornelia Huck)
> > ---
> >  Documentation/vfio-mediated-device.txt | 113 +++++++++++++++++++++++++
> >  1 file changed, 113 insertions(+)
> > 
> 
> While I probably would have written a more compact description, your
> version is fine with me as well.
> 
> Reviewed-by: Cornelia Huck <address@hidden>
Thank you Cornelia!

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