[libvirt] [RFC PATCH v1 1/1] Add attribute multiple_mdev_support for mdev type-id

[Kirti Wankhede]

Generally a single instance of mdev device, a share of physical device, is
assigned to user space application or a VM. There are cases when multiple
instances of mdev devices of same or different types are required by User
space application or VM. For example in case of vGPU, multiple mdev devices
of type which represents whole GPU can be assigned to one instance of
application or VM.

All types of mdev devices may not support assigning multiple mdev devices
to a user space application. In that case vendor driver can fail open()
call of mdev device. But there is no way to know User space application
about the configuration supported by vendor driver.

To expose supported configuration, vendor driver should add
'multiple_mdev_support' attribute to type-id directory if vendor driver
supports assigning multiple mdev devices of a particular type-id to one
instance of user space application or a VM.

User space application should read if 'multiple_mdev_support' attibute is
present in type-id directory of all mdev devices which are going to be
used. If all read 1 then user space application can proceed with multiple
mdev devices.

This is optional and readonly attribute.

Signed-off-by: Neo Jia <cjia at nvidia.com>
Signed-off-by: Kirti Wankhede <kwankhede at nvidia.com>
---
 Documentation/ABI/testing/sysfs-bus-vfio-mdev | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-bus-vfio-mdev b/Documentation/ABI/testing/sysfs-bus-vfio-mdev
index 452dbe39270e..69e1291479ce 100644
--- a/Documentation/ABI/testing/sysfs-bus-vfio-mdev
+++ b/Documentation/ABI/testing/sysfs-bus-vfio-mdev
@@ -85,6 +85,19 @@ Users:
 		a particular <type-id> that can help in understanding the
 		features provided by that type of mediated device.
 
+What:           /sys/.../mdev_supported_types/<type-id>/multiple_mdev_support
+Date:           September 2018
+Contact:        Kirti Wankhede <kwankhede at nvidia.com>
+Description:
+		Reading this attribute will return 0 or 1. Returning 1 indicates
+		multiple mdev devices of a particular <type-id> assigned to one
+		User space application is supported by vendor driver. This is
+		optional and readonly attribute.
+Users:
+		Userspace applications interested in knowing if multiple mdev
+		devices of a particular <type-id> can be assigned to one
+		instance of application.
+
 What:           /sys/.../<device>/<UUID>/
 Date:           October 2016
 Contact:        Kirti Wankhede <kwankhede at nvidia.com>
-- 
2.7.0