ReadonlyFilesystem Condition with Auto-Recovery Detection

[CharudathGopal]

ISSUE: #474

Problem Statement
The existing NPD SystemLogMonitor for ReadonlyFilesystem is a one-way trigger: it sets the condition to True when detecting Remounting filesystem read-only in kernel logs, but never clears it. The condition remains stuck until NPD pod restart or node reboot, causing some Kubernetes platform to delete the node.

Solution: CustomPluginMonitor with Active Recovery Detection

This PR introduces a CustomPluginMonitor (check_ro_filesystem.sh) that actively monitors both detection and recovery of read-only filesystems.

Key Features

1. NPD Design Adherence & Detection (5-minute lookback)

   • Mimics NPD's SystemLogMonitor by scanning /dev/kmsg for "Remounting filesystem read-only" messages
   • Uses 5-minute lookback window (300 seconds) calculated from /proc/uptime
   • Filters kernel messages by timestamp to match NPD's behavior
   • Extracts device names from kernel messages (e.g., pxd!pxd208624217308167071, dm-3, sda1)
   • Checks if extracted devices are currently mounted read-only in /host/proc/1/mounts
   • If any device is RO: Exit 1 → Condition = True

2. Recovery Check (all-time lookback)

   • If no recent errors found, performs second scan of /dev/kmsg with no time limit
   • Retrieves ALL historical "remounting filesystem read-only" messages since boot
   • Checks if ANY historically-problematic devices are still mounted read-only
   • If all devices recovered or unmounted: Exit 0 → Condition = False
   • Enables automatic recovery detection - the key differentiator from SystemLogMonitor

3. Targeted Approach (Avoids False Positives)

   • Only monitors devices that kernel explicitly reported as having errors
   • Does NOT scan all mounts in /proc/mounts (which would flag legitimate read-only mounts like /boot, CD-ROMs, ConfigMaps)
   • More accurate and simpler than filesystem-wide scanning
   • Prevents false positives from intentionally read-only filesystems

Deployment Changes

ReadonlyFilesystem CustomPluginMonitor is not enabled by default, users can enable this feature by following steps documented in docs/readonly-recovery-plugin-monitor.md

• Adds /host/proc volume mount to access host mount table
• Replace --config.system-log-monitor=/config/readonly-monitor.json with --config.custom-plugin-monitor=/config/readonly-recovery-plugin-monitor.json

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[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: CharudathGopal
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[CharudathGopal]

@Random-Liu @sjenning Can you please take a look at this PR