linux: do not use errno without failure

[giuseppe]

Closes: #1994

[gemini-code-assist]

Summary of Changes

Hello @giuseppe, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request refines the error reporting mechanism within the libcrun library by ensuring that the errno global variable is only captured and reported when a system call truly indicates a failure. Previously, errno might have been used in situations that were not actual error conditions, leading to potentially misleading error messages. The changes improve the precision of error diagnostics by aligning errno usage with actual system call failures, addressing issue #1994.

Highlights

• Error Reporting Refinement: Modified crun_make_error calls to ensure errno is only used when a system call explicitly indicates an error (return value less than 0).
• Preventing Misleading Errors: This change prevents errno from being reported in non-error scenarios, such as when read returns 0 (end-of-file) or a partial read, which do not set errno.
• Improved Error Context: Enhances the accuracy of error messages by providing a relevant errno value only when an actual system call failure occurs.

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Changelog

• src/libcrun/linux.c
  • Updated expect_success_from_sync_socket to pass errno to crun_make_error only if the read call returns a negative value, otherwise 0.
  • Updated libcrun_run_linux_container to pass errno to crun_make_error only if the read call returns a negative value, otherwise 0.

Activity

• The pull request addresses and closes issue linux: errno used after success #1994, indicating a fix for a reported problem.
• No other review comments or discussions have been provided in the context.

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[gemini-code-assist]

Code Review

This pull request addresses a bug where errno was being used to create an error message even when the read() call did not fail but simply returned fewer bytes than requested. The changes correctly ensure that errno is only used when read() returns a negative value, indicating a true error. This prevents potentially misleading error messages caused by stale errno values. The fix is applied in two similar locations, expect_success_from_sync_socket and libcrun_run_linux_container. The changes are correct and effectively resolve the issue.

[packit-as-a-service]

Ephemeral COPR build failed. @containers/packit-build please check.

[packit-as-a-service]

TMT tests failed. @containers/packit-build please check.

[eriksjolund]

Does this one need a similar fix?

crun/src/libcrun/container.c

Lines 4177 to 4180 in d0c1224

	resources = make_runtime_spec_schema_config_linux_resources (tree, &ctx, &parser_err);
	if (UNLIKELY (resources == NULL))
	{
	ret = crun_make_error (err, errno, "cannot parse resources: %s", parser_err);

[packit-as-a-service]

Ephemeral COPR build failed. @containers/packit-build please check.

[packit-as-a-service]

TMT tests failed. @containers/packit-build please check.

[eriksjolund]

LGTM

Side note: you can get more issue-PR links by editing #2006 (comment)
and adding more Closes: lines