nvidia: skip services when hardware is absent

meta-dstack/recipes-core/images/dstack-rootfs-nvidia.inc

@@ -1,6 +1,7 @@
 NVIDIA_GROUP = "acpid \
     nvidia \
     nvidia-firmware \
+    nvidia-gpu-detect \
     nvidia-persistenced \
     nvidia-fabricmanager \
     libnvidia-nscq \

meta-nvidia/recipes-graphics/nvidia/files/nvidia-fabricmanager-nvswitch-condition.conf

@@ -0,0 +1,6 @@
+# Skip the fabric manager cleanly on hosts without NVSwitch (i.e. any non
+# HGX/DGX instance, including GPU instances that have no NVSwitch) instead of
+# letting it fail. ExecCondition exit 1 -> systemd marks the unit as skipped,
+# not failed.
+[Service]
+ExecCondition=/usr/bin/nvidia-gpu-detect nvswitch

meta-nvidia/recipes-graphics/nvidia/files/nvidia-gpu-detect

@@ -0,0 +1,51 @@
+#!/bin/sh
+# nvidia-gpu-detect - report NVIDIA GPU / NVSwitch presence via sysfs PCI.
+#
+# Intended for use as a systemd ExecCondition= so that GPU-only services skip
+# cleanly (instead of failing) on instances without a GPU / without NVSwitch.
+# This lets the NVIDIA and plain images be merged into a single image.
+#
+#   exit 0 -> hardware present     (systemd runs the unit)
+#   exit 1 -> hardware absent      (systemd skips the unit, no failure)
+#
+# Detection mirrors scripts/bin/enable_vfio_passthrough.sh, but reads PCI class
+# codes from sysfs so it works before the nvidia driver is loaded and without
+# relying on lspci / the pci.ids name database:
+#
+#   GPU      = NVIDIA (0x10de) VGA (0x0300xx) or 3D controller (0x0302xx)
+#   NVSwitch = NVIDIA (0x10de) bridge          (0x06xxxx, any bridge subclass)
+#
+# NVSwitch matches any NVIDIA bridge-class device (mirrors the `grep 'Bridge'`
+# heuristic in scripts/bin/enable_vfio_passthrough.sh) rather than only the
+# "Other bridge" subclass 0x0680, so it stays correct if a future NVSwitch
+# enumerates under a different bridge subclass. This is safe here because these
+# images run as TDX guests whose only NVIDIA-vendor devices are passed-through
+# GPUs (class 0x03xx) and NVSwitches (class 0x06xx).
+
+NVIDIA_VENDOR="0x10de"
+
+# match_vendor_class <class-glob>: succeed if any PCI device has NVIDIA's
+# vendor id and a class matching the given glob (e.g. "0x0302*").
+match_vendor_class() {
+    for dev in /sys/bus/pci/devices/*; do
+        [ -r "$dev/vendor" ] && [ -r "$dev/class" ] || continue
+        [ "$(cat "$dev/vendor")" = "$NVIDIA_VENDOR" ] || continue
+        case "$(cat "$dev/class")" in
+            $1) return 0 ;;
+        esac
+    done
+    return 1
+}
+
+case "${1:-gpu}" in
+    gpu)
+        match_vendor_class '0x0300*' || match_vendor_class '0x0302*'
+        ;;
+    nvswitch)
+        match_vendor_class '0x06*'
+        ;;
+    *)
+        echo "usage: ${0##*/} {gpu|nvswitch}" >&2
+        exit 64
+        ;;
+esac

meta-nvidia/recipes-graphics/nvidia/files/nvidia-persistenced.service

@@ -6,6 +6,9 @@ After=systemd-modules-load.service modprobe@.service
 
 [Service]
 Type=oneshot
+# Skip cleanly on instances without an NVIDIA GPU (exit 1 -> unit skipped, not
+# failed), so the NVIDIA image can run on GPU-less hosts.
+ExecCondition=/usr/bin/nvidia-gpu-detect gpu
 ExecStart=/usr/bin/env nvidia-persistenced --uvm-persistence-mode
 ExecStartPost=/usr/bin/nvidia-smi conf-compute -srs 1
 RemainAfterExit=yes

meta-nvidia/recipes-graphics/nvidia/nvidia-fabricmanager_%.bbappend

@@ -0,0 +1,15 @@
+FILESEXTRAPATHS:prepend := "${THISDIR}/files:"
+
+# Only start the fabric manager when NVSwitch hardware is present, so the
+# service is silently skipped (not failed) on non-NVSwitch instances.
+SRC_URI += "file://nvidia-fabricmanager-nvswitch-condition.conf"
+
+RDEPENDS:${PN} += "nvidia-gpu-detect"
+
+do_install:append() {
+    install -d ${D}${systemd_system_unitdir}/nvidia-fabricmanager.service.d
+    install -m 0644 ${UNPACKDIR}/nvidia-fabricmanager-nvswitch-condition.conf \
+        ${D}${systemd_system_unitdir}/nvidia-fabricmanager.service.d/10-nvswitch-condition.conf
+}
+
+FILES:${PN} += "${systemd_system_unitdir}/nvidia-fabricmanager.service.d/10-nvswitch-condition.conf"

meta-nvidia/recipes-graphics/nvidia/nvidia-gpu-detect_1.0.bb

@@ -0,0 +1,16 @@
+SUMMARY = "Detect NVIDIA GPU / NVSwitch presence for conditional systemd services"
+DESCRIPTION = "Small sysfs-based helper used as a systemd ExecCondition= so that \
+GPU-only services (nvidia-persistenced, nvidia-fabricmanager) skip cleanly on \
+instances without a GPU or without NVSwitch, allowing a single merged image."
+LICENSE = "CLOSED"
+
+SRC_URI = "file://nvidia-gpu-detect"
+
+S = "${UNPACKDIR}"
+
+do_install() {
+    install -d ${D}${bindir}
+    install -m 0755 ${UNPACKDIR}/nvidia-gpu-detect ${D}${bindir}/nvidia-gpu-detect
+}
+
+FILES:${PN} = "${bindir}/nvidia-gpu-detect"

meta-nvidia/recipes-graphics/nvidia/nvidia-persistenced_1.0.bb

@@ -9,6 +9,8 @@ S = "${UNPACKDIR}"
 
 inherit systemd
 
+RDEPENDS:${PN} += "nvidia-gpu-detect"
+
 SYSTEMD_PACKAGES = "${PN}"
 SYSTEMD_SERVICE:${PN} = "nvidia-persistenced.service"
 SYSTEMD_AUTO_ENABLE:${PN} = "enable"