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

首先阅读 issue 136156 中的相关讨论和链接的 PR 136417，然后检查 os.link() 当前如何公开 linkat() 和 AT_SYMLINK_FOLLOW。完成的标准是实现 os.linkat() 的拟议行为以及 AT_FDCWD、AT_SYMLINK_FOLLOW 和 AT_EMPTY_PATH 常量，并进行适当的平台处理。