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Fix root UUID detection for device-mapper/LUKS systems #43

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Fix root UUID detection for device-mapper/LUKS systems #43

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41 changes: 35 additions & 6 deletions kernelstub/drive.py
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Original file line number Diff line number Diff line change
Expand Up @@ -22,7 +22,7 @@
terms.
"""

import os, logging, subprocess
import os, logging, subprocess, re

class NoBlockDevError(Exception):
pass
Expand Down Expand Up @@ -104,12 +104,41 @@ def get_drive_dev(self, esp):

def get_uuid(self, path):
self.log.debug('Looking for UUID for path %s' % path)

# 1. Try findmnt for UUID directly
try:
args = ['findmnt', '-n', '-o', 'UUID', '--mountpoint', path]
result = subprocess.run(args, stdout=subprocess.PIPE)
uuid = result.stdout.decode('ASCII')
uuid = uuid.strip()
return uuid
except OSError as e:
raise UUIDNotFoundError from e
uuid = result.stdout.decode('ASCII').strip()
if uuid:
return uuid
except OSError:
pass

# 2. Try findmnt SOURCE -> blkid
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@isantop isantop Jan 3, 2026

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Is there any reason this is being handled after the existing code? If we need to add the -n flag, we should just add it instead of failing without it and falling back on nearly identical code.

try:
args = ['findmnt', '-n', '-o', 'SOURCE', '--mountpoint', path]
result = subprocess.run(args, stdout=subprocess.PIPE)
src = result.stdout.decode('ASCII').strip()
if src:
args = ['blkid', '-s', 'UUID', '-o', 'value', src]
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@isantop isantop Jan 3, 2026

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On my machine, this command does not return anything regardless of what UUID I feed it. It just exits with status 2.

result = subprocess.run(args, stdout=subprocess.PIPE)
uuid = result.stdout.decode('ASCII').strip()
if uuid:
return uuid
except OSError:
pass

# 3. If path is root, try /proc/cmdline
if path == '/':
try:
with open("/proc/cmdline", "r") as f:
cmdline = f.read()
match = re.search(r"\broot=UUID=([0-9a-fA-F-]{36})\b", cmdline)
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@isantop isantop Jan 3, 2026

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This is not a good method to determine the UUID required. If kernelstub is running on a live system, this method will always fail.

if match:
return match.group(1)
except Exception:
pass

raise UUIDNotFoundError('Could not determine UUID for %s' % path)