fix(i2c): prevent file descriptor leak in SMBus usage

[gaojulong]

Tested on Raspberry Pi with repeated I2C scans.

Fix a file descriptor leak in check_for_i2c_device.

SMBus instances were opened without being closed, causing file descriptors to accumulate over time. In long-running scenarios, this could reach the system ulimit and trigger:

OSError: [Errno 24] Too many open files

As a result, flight controller boards may fail to be detected or become inaccessible.

Changes

• Use context manager (with SMBus(...) as bus) to ensure proper cleanup

Impact

• Prevents FD exhaustion
• Improves reliability of board detection

Summary by Sourcery

Bug Fixes:

• Fix a file descriptor leak in I2C SMBus usage during device detection that could lead to exhausting available file handles.

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Note

Low Risk
Small, localized resource-management change that preserves existing behavior while reducing the chance of FD exhaustion during repeated I2C scans.

Overview
Prevents file descriptor leaks during I2C probing by switching LinuxFlightController.check_for_i2c_device to use with SMBus(bus_number) as bus so the bus handle is always closed after each check.

This improves reliability of repeated board-detection scans that call check_for_i2c_device (e.g., in navigator.py) by avoiding exhaustion of open file descriptors.

^{Reviewed by Cursor Bugbot for commit 59240a8. Bugbot is set up for automated code reviews on this repo. Configure here.}

[sourcery-ai]

Reviewer's guide (collapsed on small PRs)

Reviewer's Guide

Ensures I2C SMBus file descriptors are properly closed in Linux flight controller detection by using a context manager around SMBus usage in the I2C device check helper.

Sequence diagram for I2C device check with SMBus context manager

sequenceDiagram
    participant FlightControllerDetector
    participant LinuxBoards
    participant SMBus

    FlightControllerDetector->>LinuxBoards: check_for_i2c_device(bus_number, address)
    activate LinuxBoards
    LinuxBoards->>SMBus: __enter__() via with SMBus(bus_number)
    activate SMBus
    SMBus-->>LinuxBoards: bus instance
    LinuxBoards->>SMBus: read_byte_data(address, 0)
    SMBus-->>LinuxBoards: data or raise OSError
    alt read succeeded
        LinuxBoards->>SMBus: __exit__()
        LinuxBoards-->>FlightControllerDetector: True
    else OSError raised
        LinuxBoards->>SMBus: __exit__()
        LinuxBoards-->>FlightControllerDetector: False
    end
    deactivate SMBus
    deactivate LinuxBoards

Loading

Class diagram for LinuxBoards I2C device check using SMBus context manager

classDiagram
    class LinuxBoards {
        +check_for_i2c_device(bus_number int, address int) bool
    }

    class SMBus {
        +SMBus(bus_number int)
        +__enter__() SMBus
        +__exit__(exc_type object, exc_value object, traceback object) bool
        +read_byte_data(address int, register int) int
    }

    LinuxBoards ..> SMBus : uses_with_context_manager

Loading

File-Level Changes

Change	Details	Files
Ensure SMBus file descriptors are not leaked during I2C device detection.	Wrap SMBus(bus_number) usage in a with-statement context manager in the I2C device check helper Retain the read_byte_data call inside the context block and keep existing OSError handling to signal missing/inaccessible devices	core/services/ardupilot_manager/flight_controller_detector/linux/linux_boards.py

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[patrickelectric]

Thanks @gaojulong!

[joaoantoniocardoso]

@patrickelectric should we backport it to 1.4?

[patrickelectric]

Not sure, I would prefer not since this touches a really sensible part of the vehicle.
We can release another minor release after stable if necessary with more fixes.