Don't install DCGM if the driver has been blacklisted

If the sysadmin wants to pass the gpu to a virtual instance via pci
passthrough, they will need to make the gpu unavailable to the host
system by blacklisting[0] the kernel driver. On such a system DCGM would
not be able to function and should therefore not be deployed.

This commit makes the NVIDIA gpu verifier more strict by only marking
DCGM as an available tool if both an NVIDIA gpu is detected *and* the
kernel module is not blacklisted.

[0] https://wiki.debian.org/KernelModuleBlacklisting

src/hw_tools.py

@@ -5,10 +5,13 @@
 
 import logging
 import os
+import re
 import shutil
 import stat
 import subprocess
 from abc import ABCMeta, abstractmethod
+from glob import iglob
+from itertools import chain
 from pathlib import Path
 from typing import Dict, List, Set, Tuple
 
@@ -669,9 +672,31 @@ def disk_hw_verifier() -> Set[HWTool]:
 
 
 def nvidia_gpu_verifier() -> Set[HWTool]:
-    """Verify if the hardware has NVIDIA gpu."""
+    """Verify if the hardware has NVIDIA gpu and the driver is not blacklisted.
+
+    If the sysadmin has blacklisted the nvidia driver (e.g. to configure pci passthrough)
+    DCGM won't be able to manage the GPU
+    """
     gpus = lshw(class_filter="display")
-    return {HWTool.DCGM for gpu in gpus if "nvidia" in gpu.get("vendor", "").lower()}
+    return {
+        HWTool.DCGM
+        for gpu in gpus
+        if "nvidia" in gpu.get("vendor", "").lower() and not _is_nvidia_module_blacklisted()
+    }
+
+
+def _is_nvidia_module_blacklisted() -> bool:
+    module_re = re.compile(r"blacklist\s+nvidia")
+    for conffile in chain(iglob("/etc/modprobe.d/*.conf"), "/etc/modprobe.conf"):
+        try:
+            with open(conffile, "r", encoding="utf-8") as fd:
+                for line in fd.readline():
+                    if module_re.match(line):
+                        return True
+        except (IsADirectoryError, FileNotFoundError):
+            # glob may match directories, and modprobe.conf may or may not exist
+            continue
+    return False
 
 
 def detect_available_tools() -> Set[HWTool]: