Add os.linkat() function to create a hard link with flags

Feature or enhancement

Proposal:

os.link() can call linkat() but it only supports AT_SYMLINK_FOLLOW flag (follow_symlinks=True), it doesn't support AT_EMPTY_PATH. I propose adding the os.linkat() function to create a hard link with flags, and add the following constants:

• os.AT_FDCWD
• os.AT_SYMLINK_FOLLOW
• os.AT_EMPTY_PATH

AT_EMPTY_PATH allows creating a hard link from an unnamed name even if /proc is not mounted.

Has this already been discussed elsewhere?

No response given

Links to previous discussion of this feature:

https://github.com/python/cpython/issues/136156

Linked PRs

• gh-136417

先閱讀 issue 136156 中的相關討論和連結的 PR 136417，然後檢查 os.link() 目前如何公開 linkat() 和 AT_SYMLINK_FOLLOW。完成的標準是實作 os.linkat() 的提議行為以及 AT_FDCWD、AT_SYMLINK_FOLLOW 和 AT_EMPTY_PATH 常數，並進行適當的平台處理。