feat: increase vhci-hcd capacity to 128 USB/IP devices (16 ports × 4 controllers)

[yaroslavborbat]

Description

This PR updates the init container logic for DRA to dynamically build and load patched USB/IP kernel modules (usbip-core, usbip-host, vhci-hcd) at startup with increased scalability limits.

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The Problem

The vhci-hcd driver:

• Creates two virtual USB hubs per controller (USB 2.0 and USB 3.0)
• Defaults to 8 ports per hub
• Uses 1 virtual host controller by default

This limits the total number of simultaneously attached remote USB devices to:

1 controller × 2 hubs × 8 ports = 16 devices

This becomes a bottleneck for high-density USB/IP workloads.

Additionally, the maximum number of ports per hub is constrained by the kernel constant USB_MAXCHILDREN, which is defined as 31 in the Linux USB specification headers. This means the number of ports per hub cannot exceed 31, regardless of vhci-hcd configuration.

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The Solution

We patch the vhci-hcd driver to:

• Increase the number of ports per hub from 8 to 16
• Increase the number of virtual host controllers from 1 to 4
• Remove dependency on CONFIG_USBIP_VHCI_HC_PORTS
• Remove dependency on CONFIG_USBIP_VHCI_NR_HCS
• Hardcode the new values at compile time

New total capacity:

4 controllers × 2 hubs × 16 ports = 128 devices per node

The selected value (16 ports per hub) remains safely below the kernel-enforced maximum of 31 ports.

This provides significantly higher USB device density while preserving kernel constraints.

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How It Works

• At DRA startup, the init container dynamically builds the patched modules for the host kernel version (supports 5.x and 6.x kernels)
• If the build succeeds — the custom modules are loaded with the new limits (4 controllers, 16 ports per hub)
• If the build fails — the system falls back to the default host modules (1 controller, 8 ports per hub)

Checklist

• The code is covered by unit tests.
• e2e tests passed.
• Documentation updated according to the changes.
• Changes were tested in the Kubernetes cluster manually.

Changelog entries

section: vm
type: feature
summary: Increase `vhci-hcd` capacity to 16 ports per hub and 4 controllers (up to 128 USB/IP devices per node).

[diafour]

Add a gap between the license and the documentation.

Suggested change

	# Unless required by applicable law or agreed to in writing, software
	# distributed under the License is distributed on an "AS IS" BASIS,
	# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	# See the License for the specific language governing permissions and
	# limitations under the License.
	# Build usbip-core, usbip-host, vhci-hcd for the running kernel and put .ko into a tmp dir.
	# Needs: kernel headers (e.g. linux-headers-$(uname -r)), make, gcc. No full kernel source.
	#
	# Usage:
	# Unless required by applicable law or agreed to in writing, software
	# distributed under the License is distributed on an "AS IS" BASIS,
	# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	# See the License for the specific language governing permissions and
	# limitations under the License.
	# Purpose:
	# Build usbip-core, usbip-host, vhci-hcd for the running kernel and put .ko into a tmp dir.
	#
	# Requirements:
	# - kernel headers (e.g. apt install linux-headers-$(uname -r)) (Full kernel source is not required)
	# - make
	# - gcc
	# - bash
	#
	# Usage:

[diafour]

Already noted above.

Suggested change

	#
	# Minimal deps: bash, make, gcc, kernel headers package (e.g. linux-headers-${KVER}).