Add per-container io.max throttling support (cgroups v2)

[vpetrinski]

Generated with AI assistance.

• Add IOMaxReadBps/WriteBps/ReadIOPS/WriteIOPS to Limits struct
• Apply throttle on all real block devices when cgroups v2 is active
• getAllBlockDevices() reads /sys/block, filters loop/ram/dm
• New CLI flags: container-io-max-{read,write}-{bps,iops}
• Zero values = disabled (backward compatible)

Companion PR in garden-runc-release: https://github.com/vpetrinski/garden-runc-release/tree/feature/io-max-throttling

• Read the Contributing document.

  Summary

  Adds per-container disk I/O rate limiting via cgroups v2 io.max. When configured, each new container receives IOPS and throughput limits on all real block devices at creation time.

  Motivation: A single container can saturate the shared data disk on a Diego cell, starving all other containers of I/O and causing health check timeouts / false app crashes.

  Changes:

  • rundmc/bundlerules/limits.go: Extended Limits struct with IOMaxReadBps, IOMaxWriteBps, IOMaxReadIOPS, IOMaxWriteIOPS. When any value > 0 and cgroups v2 is active, applies throttle devices to the OCI
    bundle for all real block devices.
  • guardiancmd/command.go: Added 4 new CLI flags (--container-io-max-{read,write}-{bps,iops})
  • getAllBlockDevices(): Reads /sys/block, filters virtual devices (loop, ram, dm), returns major:minor for real devices.

  Tested: Custom dev release deployed on Noble cell (Ubuntu 24.04, cgroups v2). Throttled: 60 MB/s vs Unthrottled: 272 MB/s (4.5× protection). App starts and runs normally with limits active.

  Companion PR in garden-runc-release: cloudfoundry/garden-runc-release@develop...vpetrinski:garden-runc-release:feature/io-max-throttling

  Generated with AI assistance.

  Backward Compatibility

  Breaking Change? No

  • All new flags default to 0 (unlimited) — no behavioral change unless operator explicitly sets values > 0
  • On cgroups v1 (Jammy) and Windows: silently skipped via IsCgroup2UnifiedMode() check
  • Existing containers and configurations are completely unaffected
  • Feature is opt-in only