fix: Properly handle RDMA subsystem's shared and exclusive mode

An RDMA device can only be assigned to a network namespace when the RDMA
subsystem is set to an "exclusive" network namespace mode. When the subsystem is
set to "shared" mode, an attempt to assign an RDMA device to a network namespace
will result in failure. Additionally, "If there are active network namespaces
and if one or more RDMA devices exist, changing mode from shared to exclusive
returns error code EBUSY."

Ref. https://man7.org/linux/man-pages/man8/rdma-system.8.html

Author: gauravkghildiyal

pkg/driver/rdmadevice.go

@@ -21,12 +21,39 @@ import (
 
 	"github.com/vishvananda/netlink"
 	"github.com/vishvananda/netns"
+	"k8s.io/klog/v2"
+)
+
+const (
+	// rdmaNetnsModeShared and rdmaNetnsModeExclusive define the RDMA subsystem
+	// network namespace mode. An RDMA device can only be assigned to a network
+	// namespace when the RDMA subsystem is set to an "exclusive" network
+	// namespace mode. When the subsystem is set to "shared" mode, an attempt to
+	// assign an RDMA device to a network namespace will result in failure.
+	// Additionally, "If there are active network namespaces and if one or more
+	// RDMA devices exist, changing mode from shared to exclusive returns error
+	// code EBUSY."
+	//
+	// Ref. https://man7.org/linux/man-pages/man8/rdma-system.8.html
+	rdmaNetnsModeShared    = "shared"
+	rdmaNetnsModeExclusive = "exclusive"
 )
 
 // Based on existing RDMA CNI plugin
 // https://github.com/k8snetworkplumbingwg/rdma-cni
 
 func nsAttachRdmadev(hostIfName string, containerNsPAth string) error {
+	rdmaNetnsMode, err := netlink.RdmaSystemGetNetnsMode()
+	if err != nil {
+		return fmt.Errorf("failed to determine the RDMA subsystem's network namespace mode: %w", err)
+	}
+	if rdmaNetnsMode == rdmaNetnsModeShared {
+		// TODO: Potentially move this check to the function invokers side for
+		// improved visiblity and expectation of what this function does.
+		klog.Info("Skipping setting network namespace for RDMA device since RDMA sybsystem is currently configured for shared mode.")
+		return nil
+	}
+
 	containerNs, err := netns.GetFromPath(containerNsPAth)
 	if err != nil {
 		return fmt.Errorf("could not get network namespace from path %s for network device %s : %w", containerNsPAth, hostIfName, err)