Collect IOMMU group per PCIe device from sysfs

Reads the iommu_group symlink for each BDF and exposes the group number
as iommu_group in the hardware snapshot JSON.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

audit/internal/collector/pcie.go

@@ -4,7 +4,9 @@ import (
 	"bee/audit/internal/schema"
 	"fmt"
 	"log/slog"
+	"os"
 	"os/exec"
+	"path/filepath"
 	"strconv"
 	"strings"
 )
@@ -140,6 +142,9 @@ func parseLspciDevice(fields map[string]string) schema.HardwarePCIeDevice {
 		} else if numaNode, ok := parsePCINumaNode(fields["NUMANode"]); ok {
 			dev.NUMANode = &numaNode
 		}
+		if group, ok := readPCIIOMMUGroup(bdf); ok {
+			dev.IOMMUGroup = &group
+		}
 		if width, ok := readPCIIntAttribute(bdf, "current_link_width"); ok {
 			dev.LinkWidth = &width
 		}
@@ -179,6 +184,21 @@ func parseLspciDevice(fields map[string]string) schema.HardwarePCIeDevice {
 	return dev
 }
 
+// readPCIIOMMUGroup resolves the IOMMU group number for a BDF via the
+// iommu_group symlink in sysfs: .../devices/<bdf>/iommu_group -> .../kernel/iommu_groups/<N>
+func readPCIIOMMUGroup(bdf string) (int, bool) {
+	link := "/sys/bus/pci/devices/" + bdf + "/iommu_group"
+	target, err := os.Readlink(link)
+	if err != nil {
+		return 0, false
+	}
+	n, err := strconv.Atoi(filepath.Base(target))
+	if err != nil {
+		return 0, false
+	}
+	return n, true
+}
+
 // readPCIIDs reads vendor and device IDs from sysfs for a given BDF.
 func readPCIIDs(bdf string) (vendorID, deviceID int) {
 	base := "/sys/bus/pci/devices/" + bdf

audit/internal/schema/hardware.go

@@ -211,6 +211,7 @@ type HardwarePCIeDevice struct {
 	Firmware               *string        `json:"firmware,omitempty"`
 	MacAddresses           []string       `json:"mac_addresses,omitempty"`
 	Present                *bool          `json:"present,omitempty"`
+	IOMMUGroup             *int           `json:"iommu_group,omitempty"`
 	Telemetry              map[string]any `json:"-"`
 }