Map errno values to human-readable messages in System.Device.Gpio error handling

[Copilot]

Error messages currently show only numeric errno codes (e.g., "Error 5 performing I2C data transfer"), requiring developers to look up error meanings. This change uses Marshal.GetLastPInvokeErrorMessage() (.NET 7+) to include descriptive messages.

Changes

• ExceptionHelper: Added GetLastErrorMessage() method that captures both error code and message, formats as "code (message)"
• Error handling: Updated 22 error sites across GPIO, I2C, and SPI drivers to use centralized helper
• Code quality: Eliminated duplication, net -30 lines
• Code style: Fixed SA1028 errors by removing trailing whitespace across System.Device.Gpio

Example

Before:

throw new IOException($"Error {Marshal.GetLastWin32Error()} performing I2C data transfer.");
// Output: "Error 5 performing I2C data transfer."

After:

throw new IOException($"Error {ExceptionHelper.GetLastErrorMessage()} performing I2C data transfer.");
// Output: "Error 5 (Input/output error) performing I2C data transfer."

Notes

Three locations manually format errors where error code must be checked before throwing (EINTR/ENOENT comparisons). These are documented with inline comments explaining why GetLastWin32Error() cannot be called twice.

[!WARNING]

Original prompt

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This section details on the original issue you should resolve

<issue_title>Should we add a mapping to Marshal.GetLastWin32Error()</issue_title>
<issue_description>Our current exception handling is very obscure and difficult to understand, just like #668 . Why don't we map errors.h accordingly?</issue_description>

Comments on the Issue (you are @copilot in this section)

@krwq @ZhangGaoxing might be worth checking corefx code first to see if they already have this defined somewhere.

Possibly something using this https://github.com/dotnet/corefx/blob/ce4ceb09e0bd21675a3523edebfaf73a16714d15/src/Native/Unix/System.Native/pal_errno.c#L20</comment_new>
<comment_new>@joperezr
This makes sense and I agree it would be useful.</comment_new>
<comment_new>@krwq
[Triage] This might just work with .NET 8 but we need verification</comment_new>

• Fixes Should we add a mapping to Marshal.GetLastWin32Error() #671

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Microsoft Reviewers: Open in CodeFlow

[krwq]

@copilot please fix error SA1028: (NETCORE_ENGINEERING_TELEMETRY=Build) Code should not contain trailing whitespace with some tooling (you can run it on everything in this repo)

[Copilot]

Fixed in 0549198 - ran dotnet format whitespace across System.Device.Gpio and manually fixed remaining trailing whitespace in comments.

[krwq]

@copilot I resolved conflicts and I probably messed up the PR, please double check all changes are here

[Copilot]

@copilot I resolved conflicts and I probably messed up the PR, please double check all changes are here

I've verified all changes are present after the merge. ✅

Core changes:

• ExceptionHelper.cs: Added GetLastErrorMessage() method and GetIOException() overload
• Updated 12 files with errno-to-message mapping (22+ error sites)
• Special case handling in RaspberryPi3LinuxDriver, SysFsDriver, and LibGpiodDriverEventHandler with explanatory comments

Files with changes:

1. ExceptionHelper.cs - Core helper methods
2. LineHandle.cs, LibGpiodDriver.cs, LibGpiodDriverEventHandler.cs - GPIO error handling
3. UnixI2cBus.cs, UnixI2cFileTransferBus.cs - I2C error handling
4. UnixSpiDevice.cs - SPI error handling
5. RaspberryPi3LinuxDriver.cs, SysFsDriver.cs - Special cases with ENOENT/EINTR checks
6. LineRequest.cs, LibGpiodV2Driver.cs, UnixDriver.cs - Formatting improvements

All Marshal.GetLastWin32Error() calls now use ExceptionHelper.GetLastErrorMessage() to provide human-readable messages.

[pgrawehr]

/azp run

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