linux: handle openat error

[eriksjolund]

Fail early to make the code easier to read.

What do you think? Does it make sense?

Summary by Sourcery

Bug Fixes:

• Return a specific error when opening the parent directory component fails instead of silently continuing after access checks.

[sourcery-ai]

Reviewer's guide (collapsed on small PRs)

Reviewer's Guide

Refactors error handling around openat failure in make_parent_mount_private to fail early with a clearer, more precise error while preserving the original errno.

File-Level Changes

Change	Details	Files
Improve error handling when openat("..") fails in make_parent_mount_private to fail fast with a specific error and preserved errno.	Capture errno immediately when openat on the parent directory fails On access failure, continue to return an EACCES error indicating an inaccessible component On successful access check but open failure, return an error using the saved errno with a message indicating the component cannot be opened	src/libcrun/linux.c

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[sourcery-ai]

Hey there - I've reviewed your changes - here's some feedback:

• This change alters behavior by treating an openat failure as fatal even when the subsequent faccessat succeeds; if the intent is only to fail when the directory is inaccessible, consider whether you still want to allow execution to continue when faccessat passes but openat fails for another reason (e.g., ENFILE, EMFILE).
• Consider declaring saved_errno as const int to document that it is not modified after capturing errno and to make the intent slightly clearer.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- This change alters behavior by treating an `openat` failure as fatal even when the subsequent `faccessat` succeeds; if the intent is only to fail when the directory is inaccessible, consider whether you still want to allow execution to continue when `faccessat` passes but `openat` fails for another reason (e.g., `ENFILE`, `EMFILE`).
- Consider declaring `saved_errno` as `const int` to document that it is not modified after capturing `errno` and to make the intent slightly clearer.

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[packit-as-a-service]

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

[giuseppe]

LGTM