expose AT_EMPTY_PATH flag with linkat / LinkatFlags

[xaverdh]

Currently you can't set this flag..

This is useful in the following situation:
You create a temporary file with O_TMPFILE and without O_EXCL, then you want to link it somewhere, but have no old file path you could give linkat.

[asomers]

Yeah, that would be good. Care to submit a PR?

[xaverdh]

Ok, I will give it a try

[xaverdh]

What is the policy regarding api breakage? I am tempted to just make the oldpath argument an Option..
I can only think of two ways to preserve the api:

• introduce a new function with the new api
• make the argument polymorphic via a trait that the old LinkatFlags then implements

[SteveLauC]

What is the policy regarding api breakage?

Breaking changes can be introduced in the following 0.27 release AFAIK.

I am tempted to just make the oldpath argument an Option

It seems that this feature is exclusive to Linux and Android (fuchsia also has AT_EMPTY_PATH but I am not clear if it is supported with linkat(2)), so IMO the following interface may look weird to the users that are not on Linux and Android?

pub fn linkat<P: ?Sized + NixPath>(
    olddirfd: Option<RawFd>,
    oldpath: Option<&P>,
    newdirfd: Option<RawFd>,
    newpath: &P,
    flags: LinkatFlags,
) -> Result<()>

Thought I am not sure if it is a good idea to have a separate implementation just for Linux and Android...

[xaverdh]

Ok, so the linked pr now just swaps LinkatFlags for a bitflags based implementation. That will cause breakage of course..