iSulad Support for CDI ​

Overview ​

Container Device Interface (CDI) is a container runtime specification used to support third-party devices.

CDI solves the following problems:
In Linux, only one device node needed to be exposed in a container in the past to enable device awareness of the container. However, as devices and software become more complex, vendors want to perform more operations, such as:

• Exposing multiple device nodes to a container, mounting files from a runtime namespace to a container, or hiding procfs entries.
• Checking the compatibility between containers and devices. For example, checking whether a container can run on a specified device.
• Performing runtime-specific operations, such as virtual machines and Linux container-based runtimes.
• Performing device-specific operations, such as GPU memory cleanup and FPGA re-programming.

In the absence of third-party device standards, vendors often have to write and maintain multiple plugins for different runtimes, or even contribute vendor-specific code directly in a runtime. In addition, the runtime does not expose the plugin system in a unified manner (or even not at all), resulting in duplication of functionality in higher-level abstractions (such as Kubernetes device plugins).

To solve the preceding problem, CDI provides the following features:
CDI describes a mechanism that allows third-party vendors to interact with devices without modifying the container runtime.

The mechanism is exposed as a JSON file (similar to the container network interface CNI), which allows vendors to describe the operations that the container runtime should perform on the OCI-based container.

Currently, iSulad supports the CDI v0.6.0 specification.

Configuring iSulad to Support CDI ​

Modify the daemon.json file as follows and restart iSulad:

{
    ...
    "enable-cri-v1": true,
    "cdi-spec-dirs": ["/etc/cdi", "/var/run/cdi"],
    "enable-cdi": true
}

cdi-spec-dirs specifies the directory where CDI specifications are stored. If this parameter is not specified, the default value /etc/cdi or /var/run/cdi is used.

Examples ​

CDI Specification Example ​

For details about each field, see CDI v0.6.0.

$ mkdir /etc/cdi
$ cat > /etc/cdi/vendor.json <<EOF
{
  "cdiVersion": "0.6.0",
  "kind": "vendor.com/device",
  "devices": [
    {
      "name": "myDevice",
      "containerEdits": {
        "deviceNodes": [
          {"hostPath": "/vendor/dev/card1", "path": "/dev/card1", "type": "c", "major": 25, "minor": 25, "fileMode": 384, "permissions": "rw", "uid": 1000, "gid": 1000},
          {"path": "/dev/card-render1", "type": "c", "major": 25, "minor": 25, "fileMode": 384, "permissions": "rwm", "uid": 1000, "gid": 1000}
        ]
      }
    }
  ],
  "containerEdits": {
    "env": [
      "FOO=VALID_SPEC",
      "BAR=BARVALUE1"
    ],
    "deviceNodes": [
      {"path": "/dev/vendorctl", "type": "b", "major": 25, "minor": 25, "fileMode": 384, "permissions": "rw", "uid": 1000, "gid": 1000}
    ],
    "mounts": [
      {"hostPath": "/bin/vendorBin", "containerPath": "/bin/vendorBin"},
      {"hostPath": "/usr/lib/libVendor.so.0", "containerPath": "/usr/lib/libVendor.so.0"},
      {"hostPath": "tmpfs", "containerPath": "/tmp/data", "type": "tmpfs", "options": ["nosuid","strictatime","mode=755","size=65536k"]}
    ],
    "hooks": [
      {"createContainer": {"path": "/bin/vendor-hook"} },
      {"startContainer": {"path": "/usr/bin/ldconfig"} }
    ]
  }
}
EOF

Using CDI in the Parameters for Creating a Container in CRI ​

Assume that the vendor.json specification has been generated, and the specification is available in /etc/cdi or /var/run/cdi (or the specification is available in the directory specified by cdi-spec-dirs in the iSulad configuration file), the container can access the device using its fully qualified device name, for example, vendor.com/device=myDevice.

In the JSON file of the container, you can use either of the following methods to specify a device:

1. Specify a device in annotations.

   json

   {
       ... ...
       "annotations": [
           ... ...
           {"cdi.k8s.io/test": "vendor.com/device=myDevice"},
           ... ...
       ]
       ... ...
   }

2. Specify a device in CDI_Devices.

   json

   {
       ... ...
       "CDI_Devices": [
           ... ...
           {"Name": "vendor.com/device=myDevice"},
           ... ...
       ]
       ... ...
   }

Constraints ​

1. Currently, iSulad supports the CDI feature using CRI only.