[1.4] core: services: ardupilot_manager: Prevent i2c file descriptor leak (backport #3878)

[joaoantoniocardoso]

While working on #4121, I found the same problem already fixed on master.

Backport of #3878 (e6c97dc4a) to 1.4-dev.

check_for_i2c_device opens an SMBus and never closes it. Every failed probe leaks one /dev/i2c-* file descriptor, so on a vehicle whose Navigator is missing or unresponsive, ardupilot-manager walks the whole detector list on every available_boards call and steadily burns through the 1024 FD soft limit.

Reproduced on hardware

Raspberry Pi 4 with the Navigator removed, running current 1.4-dev:

• Board detection correctly finds no Navigator, available_boards returns SITL only.
• Within ~4 minutes the ardupilot-manager process holds 1024/1024 FDs, 1015 of them /dev/i2c-1.
• Its HTTP server then dies with OSError: [Errno 24] Too many open files on socket.accept(); GET /v1.0/board and /v1.0/available_boards stop responding entirely.
• Every rejected connection dumps a loguru backtrace, growing the ardupilot-manager log directory by roughly 20 MB/min (189 MB in 15 minutes, rotating 10 MB files every ~30 s).

A Raspberry Pi 5 with its Navigator attached, same image, stays flat at 15 FDs total (5 i2c) and under 1 MB of logs, which matches the leak being on the OSError path.

Change

Use the context manager so the bus is closed on both the success and failure paths:

with SMBus(bus_number) as bus:
    bus.read_byte_data(address, 0)

Test plan

• Reproduced FD exhaustion and API death on a Pi 4 without the Navigator on unpatched 1.4-dev
• With the patch applied on the same board (still no Navigator), 200 available_boards requests driving ~1770 detection sweeps left the FD count flat at 8 with zero open /dev/i2c-* handles, no Errno 24, API still answering 200, and the log file at 1.2 MB after several minutes

[github-actions]

Automated PR Review

0. Summary

• Verdict: LGTM

Straight backport of #3878 to 1.4-dev. Wraps SMBus(bus_number) in a with block inside check_for_i2c_device so the /dev/i2c-* file descriptor is closed on both the success and OSError paths, preventing FD exhaustion in ardupilot-manager when the Navigator is missing.

No further comments, nice job 👍

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