Re: [libvirt] [PATCH v3 1/2] vfio/mdev: add migration_version attribute for mdev device
On Sun, 26 May 2019 23:43:42 -0400
Yan Zhao <yan.y.zhao(a)intel.com> wrote:
migration_version attribute is used to check migration compatibility
between two mdev device of the same mdev type.
s/device/devices/
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 <alex.williamson(a)redhat.com>
Cc: Erik Skultety <eskultet(a)redhat.com>
Cc: "Dr. David Alan Gilbert" <dgilbert(a)redhat.com>
Cc: Cornelia Huck <cohuck(a)redhat.com>
Cc: "Tian, Kevin" <kevin.tian(a)intel.com>
Cc: Zhenyu Wang <zhenyuw(a)linux.intel.com>
Cc: "Wang, Zhi A" <zhi.a.wang(a)intel.com>
Cc: Neo Jia <cjia(a)nvidia.com>
Cc: Kirti Wankhede <kwankhede(a)nvidia.com>
Cc: Daniel P. Berrangé <berrange(a)redhat.com>
Cc: Christophe de Dinechin <dinechin(a)redhat.com>
Signed-off-by: Yan Zhao <yan.y.zhao(a)intel.com>
---
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 <cohuck(a)redhat.com>