Protect against errors when checking DM subsystem

[vojtechtrefny]

Summary by Sourcery

Handle DMError and missing subsystems gracefully in device_dm_subsystem_match to prevent unhandled exceptions

Bug Fixes:

• Catch blockdev.DMError in device_dm_subsystem_match to avoid crashes and log the error before returning False
• Return False when get_subsystem_from_name returns no result instead of proceeding

[sourcery-ai]

Reviewer's guide (collapsed on small PRs)

Reviewer's Guide

This PR enhances robustness of device_dm_subsystem_match by wrapping the DM subsystem lookup in a try/except block to catch and log DMError exceptions, falling back to False when errors or empty results occur.

Class diagram for updated error handling in device_dm_subsystem_match

classDiagram
    class device_dm_subsystem_match {
        +device_dm_subsystem_match(info, subsystem)
    }
    class blockdev.dm {
        +get_subsystem_from_name(name)
    }
    class blockdev.DMError
    device_dm_subsystem_match --> blockdev.dm : calls get_subsystem_from_name
    device_dm_subsystem_match ..> blockdev.DMError : handles exception

Loading

File-Level Changes

Change	Details	Files
Add exception handling and error logging around DM subsystem lookup	Wrap blockdev.dm.get_subsystem_from_name call in try/except Log an error message when a DMError is caught Return False immediately on exception Retain original empty-subsystem check inside the else branch	blivet/udev.py

Possibly linked issues

• Master keepers #123: The PR fixes the issue by adding error handling for blockdev.DMError when getting the DM subsystem, preventing the 'unable to get udev info' crash.

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