Subject: Re: [PATCH 0/7] Introduce vdpa management tool

From: "Michael S. Tsirkin" <[email-masked]>
Date: Wed, 16 Dec 2020 04:16:17 -0500

On Thu, Nov 12, 2020 at 08:39:58AM +0200, Parav Pandit wrote:
> This patchset covers user requirements for managing existing vdpa devices,
> using a tool and its internal design notes for kernel drivers.

I applied bugfix patches 1 and 2.
Others conflict with vdpa sim block support, pls rebase.

> Background and user requirements:
> ----------------------------------
> (1) Currently VDPA device is created by driver when driver is loaded.
> However, user should have a choice when to create or not create a vdpa device
> for the underlying parent device.
> 
> For example, mlx5 PCI VF and subfunction device supports multiple classes of
> device such netdev, vdpa, rdma. Howevever it is not required to always created
> vdpa device for such device.
> 
> (2) In another use case, a device may support creating one or multiple vdpa
> device of same or different class such as net and block.
> Creating vdpa devices at driver load time further limits this use case.
> 
> (3) A user should be able to monitor and query vdpa queue level or device level
> statistics for a given vdpa device.
> 
> (4) A user should be able to query what class of vdpa devices are supported
> by its parent device.
> 
> (5) A user should be able to view supported features and negotiated features
> of the vdpa device.
> 
> (6) A user should be able to create a vdpa device in vendor agnostic manner
> using single tool.
> 
> Hence, it is required to have a tool through which user can create one or more
> vdpa devices from a parent device which addresses above user requirements.
> 
> Example devices:
> ----------------
>  +-----------+ +-----------+ +---------+ +--------+ +-----------+ 
>  |vdpa dev 0 | |vdpa dev 1 | |rdma dev | |netdev  | |vdpa dev 3 |
>  |type=net   | |type=block | |mlx5_0   | |ens3f0  | |type=net   |
>  +----+------+ +-----+-----+ +----+----+ +-----+--+ +----+------+
>       |              |            |            |         |
>       |              |            |            |         |
>  +----+-----+        |       +----+----+       |    +----+----+
>  |  mlx5    +--------+       |mlx5     +-------+    |mlx5     |
>  |pci vf 2  |                |pci vf 4 |            |pci sf 8 |
>  |03:00:2   |                |03:00.4  |            |mlx5_sf.8|
>  +----+-----+                +----+----+            +----+----+
>       |                           |                      |
>       |                      +----+-----+                |
>       +----------------------+mlx5      +----------------+
>                              |pci pf 0  |
>                              |03:00.0   |
>                              +----------+
> 
> vdpa tool:
> ----------
> vdpa tool is a tool to create, delete vdpa devices from a parent device. It is a
> tool that enables user to query statistics, features and may be more attributes
> in future.
> 
> vdpa tool command draft:
> ------------------------
> (a) List parent devices which supports creating vdpa devices.
> It also shows which class types supported by this parent device.
> In below command example two parent devices support vdpa device creation.
> First is PCI VF whose bdf is 03.00:2.
> Second is PCI VF whose name is 03:00.4.
> Third is PCI SF whose name is mlx5_core.sf.8
> 
> $ vdpa parentdev list
> vdpasim
>   supported_classes
>     net
> pci/0000:03.00:3
>   supported_classes
>     net block
> pci/0000:03.00:4
>   supported_classes
>     net block
> auxiliary/mlx5_core.sf.8
>   supported_classes
>     net
> 
> (b) Now add a vdpa device of networking class and show the device.
> $ vdpa dev add parentdev pci/0000:03.00:2 type net name foo0 $ vdpa dev show foo0
> foo0: parentdev pci/0000:03.00:2 type network parentdev vdpasim vendor_id 0 max_vqs 2 max_vq_size 256
> 
> (c) Show features of a vdpa device
> $ vdpa dev features show foo0
> supported
>   iommu platform
>   version 1
> 
> (d) Dump vdpa device statistics
> $ vdpa dev stats show foo0
> kickdoorbells 10
> wqes 100
> 
> (e) Now delete a vdpa device previously created.
> $ vdpa dev del foo0
> 
> vdpa tool support in this patchset:
> -----------------------------------
> vdpa tool is created to create, delete and query vdpa devices.
> examples:
> Show vdpa parent device that supports creating, deleting vdpa devices.
> 
> $ vdpa parentdev show
> vdpasim:
>   supported_classes
>     net
> 
> $ vdpa parentdev show -jp
> {
>     "show": {
>        "vdpasim": {
>           "supported_classes": {
>              "net"
>         }
>     }
> }
> 
> Create a vdpa device of type networking named as "foo2" from the parent device vdpasim:
> 
> $ vdpa dev add parentdev vdpasim type net name foo2
> 
> Show the newly created vdpa device by its name:
> $ vdpa dev show foo2
> foo2: type network parentdev vdpasim vendor_id 0 max_vqs 2 max_vq_size 256
> 
> $ vdpa dev show foo2 -jp
> {
>     "dev": {
>         "foo2": {
>             "type": "network",
>             "parentdev": "vdpasim",
>             "vendor_id": 0,
>             "max_vqs": 2,
>             "max_vq_size": 256
>         }
>     }
> }
> 
> Delete the vdpa device after its use:
> $ vdpa dev del foo2
> 
> vdpa tool support by kernel:
> ----------------------------
> vdpa tool user interface will be supported by existing vdpa kernel framework,
> i.e. drivers/vdpa/vdpa.c It services user command through a netlink interface.
> 
> Each parent device registers supported callback operations with vdpa subsystem
> through which vdpa device(s) can be managed.
> 
> FAQs:
> -----
> 1. Where does userspace vdpa tool reside which users can use?
> Ans: vdpa tool can possibly reside in iproute2 [1] as it enables user to
> create vdpa net devices.
> 
> 2. Why not create and delete vdpa device using sysfs/configfs?
> Ans:
> (a) A device creation may involve passing one or more attributes.
> Passing multiple attributes and returning error code and more verbose
> information for invalid attributes cannot be handled by sysfs/configfs.
> 
> (b) netlink framework is rich that enables user space and kernel driver to
> provide nested attributes.
> 
> (c) Exposing device specific file under sysfs without net namespace
> awareness exposes details to multiple containers. Instead exposing
> attributes via a netlink socket secures the communication channel with kernel.
> 
> (d) netlink socket interface enables to run syscaller kernel tests.
> 
> 3. Why not use ioctl() interface?
> Ans: ioctl() interface replicates the necessary plumbing which already
> exists through netlink socket.
> 
> 4. What happens when one or more user created vdpa devices exist for a
> parent PCI VF or SF and such parent device is removed?
> Ans: All user created vdpa devices are removed that belong to a parent.
> 
> [1] git://git.kernel.org/pub/scm/network/iproute2/iproute2-next.git
> 
> Next steps:
> -----------
> (a) Post this patchset and iproute2/vdpa inclusion, remaining two drivers
> will be coverted to support vdpa tool instead of creating unmanaged default
> device on driver load.
> (b) More net specific parameters such as mac, mtu will be added.
> (c) Features bits get and set interface will be added.
> 
> Parav Pandit (7):
>   vdpa: Add missing comment for virtqueue count
>   vdpa: Use simpler version of ida allocation
>   vdpa: Extend routine to accept vdpa device name
>   vdpa: Define vdpa parent device, ops and a netlink interface
>   vdpa: Enable a user to add and delete a vdpa device
>   vdpa: Enable user to query vdpa device info
>   vdpa/vdpa_sim: Enable user to create vdpasim net devices
> 
>  drivers/vdpa/Kconfig              |   1 +
>  drivers/vdpa/ifcvf/ifcvf_main.c   |   2 +-
>  drivers/vdpa/mlx5/net/mlx5_vnet.c |   2 +-
>  drivers/vdpa/vdpa.c               | 511 +++++++++++++++++++++++++++++-
>  drivers/vdpa/vdpa_sim/vdpa_sim.c  |  81 ++++-
>  include/linux/vdpa.h              |  46 ++-
>  include/uapi/linux/vdpa.h         |  41 +++
>  7 files changed, 660 insertions(+), 24 deletions(-)
>  create mode 100644 include/uapi/linux/vdpa.h
> 
> -- 
> 2.26.2