[Bug]: Device or resource busy error while creating a new vm

[aniketmaurya]

What happened?

smolvm create 
Failed to create VM vm-e576f6da: Command failed: sudo -n ip tuntap add tap4 mode tap user aniket
stderr: ioctl(TUNSETIFF): Device or resource busy

╭──────────────────────────────── Error ─────────────────────────────────╮
│ Error: Command failed: sudo -n ip tuntap add tap4 mode tap user aniket │
│ stderr: ioctl(TUNSETIFF): Device or resource busy                      │
│                                                                        │
╰────────────────────────────────────────────────────────────────────────╯
(smolvm) (base) ➜  SmolVM git:(main) ✗ smolvm create 
╭─────── VM Created ────────╮
│ Created VM 'vm-5c0d9c81'. │
╰───────────────────────────╯
         VM Details         
┌────────────┬─────────────┐
│ Name       │ vm-5c0d9c81 │
│ Status     │ running     │
│ Backend    │ firecracker │
│ IP Address │ 172.16.0.4  │
│ SSH Port   │ 2202        │
└────────────┴─────────────┘
Next: smolvm ssh vm-5c0d9c81

Steps to reproduce

run smolvm create

Expected behavior

NA

SmolVM version or commit

main

Environment

Linux + Firecracker

Relevant logs or output

[aniketmaurya]

@codex please fix this

[chatgpt-codex-connector]

Summary

• Added transient-retry handling to TAP creation in NetworkManager.create_tap(): when ip tuntap add fails with Device or resource busy / EBUSY, SmolVM now retries up to 3 times with short incremental backoff before failing, while preserving idempotent success for File exists / EEXIST.
• Added dedicated TAP-management tests to validate:
  • existing TAP behavior remains idempotent,
  • transient busy errors retry then succeed,
  • persistent busy errors raise after retry exhaustion.
• Committed the changes on the current branch (3627841) and created a follow-up PR via the make_pr tool summarizing this fix.

Testing

• ⚠️ pytest -q tests/test_network.py (fails in this environment because existing tests attempt to write /proc/sys/net/ipv4/ip_forward, which is read-only here).
• ✅ PYTHONPATH=src pytest -q tests/test_network.py -k 'TestTapManagement'
• ✅ python -m compileall -q src tests

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