add listxattr/getxattr/setxattr/removexattr on Linux and Android

[SteveLauC]

What this PR does:

This PR adds listxattr, getxattr, setxattr, removexattr and their variants on Linux and Android

pub fn listxattr<P: ?Sized + NixPath>(path: &P) -> Result<Vec<OsString>>
pub fn llistxattr<P: ?Sized + NixPath>(path: &P) -> Result<Vec<OsString>>
pub fn flistxattr(fd: RawFd) -> Result<Vec<OsString>>

pub fn getxattr<P, S>(path: &P, name: S) -> Result<Vec<u8>>
pub fn lgetxattr<P, S>(path: &P, name: S) -> Result<Vec<u8>>
pub fn fgetxattr<S>(fd: RawFd, name: S) -> Result<Vec<u8>>

pub fn setxattr<P, S, B>(
    path: &P,
    name: S,
    value: B,
    flags: SetxattrFlag,
) -> Result<()>
pub fn lsetxattr<P, S, B>(
    path: &P,
    name: S,
    value: B,
    flags: SetxattrFlag,
) -> Result<()>
pub fn fsetxattr<S, B>(
    fd: RawFd,
    name: S,
    value: B,
    flags: SetxattrFlag,
) -> Result<()>

pub fn removexattr<P, S>(path: &P, name: S) -> Result<()>
pub fn lremovexattr<P, S>(path: &P, name: S) -> Result<()>
pub fn fremovexattr<S>(fd: RawFd, name: S) -> Result<()>

man pages

• listxattr man page
• getxattr man page
• setxattr man page
• removexattr man page

What about other platforms

NetBSD should also be added in this PR, but their current libc bindings are wrong.

Update: I just found that NetBSD has another collection of xattr APIs, which is compatible with FreeBSD, and the libc bindings are added in libc#1114. Then I prefer to put these two BSD OSes together.

Module

These APIs are placed in sys/xattr.rs

Tests

Tests are placed in test/sys/test-xattr.rs. Symbolic link versions of APIs are not covered.

If they should be covered, I will add them.

pub fn llistxattr<P: ?Sized + NixPath>(path: &P) -> Result<Vec<OsString>>
pub fn lgetxattr<P, S>(path: &P, name: S) -> Result<Vec<u8>>
pub fn lsetxattr<P, S>(
    path: &P,
    name: S,
    value: B,
    flags: SetxattrFlag,
) -> Result<()>
pub fn lremovexattr<P, S>(path: &P, name: S) -> Result<()>

In the tests, temporary directory are created in the current working directory instead of under /tmp, this is needed because we need to test user EA, tmpfs does not support this, see this answer.

[asomers]

I haven't read the whole PR yet. But does this have any advantages over the existing xattr crate?

[SteveLauC]

I haven't read the whole PR yet. But does this have any advantages over the existing xattr crate?

Yes, it has some minor advantages, see Why another crate for EA? Any difference from xattr.

As you can see, I have made a dedicated crate for this, and have almost all the platforms supported. If you want it to be merged into nix, I am happy to contribute. If you don't, feel free to close this PR.

[asomers]

Yes, it has some minor advantages, see Why another crate for EA? Any difference from xattr.

As you can see, I have made a dedicated crate for this, and have almost all the platforms supported. If you want it to be merged into nix, I am happy to contribute. If you don't, feel free to close this PR.

And this PR merges the entirety of your extattr crate into Nix? Are you intending to shut down the other one?

[SteveLauC]

And this PR merges the entirety of your extattr crate into Nix?

I have no strong view on this, it depends on if nix wants it or not. It does not matter whether these bindings exist in nix or extattr as long as Rust users have such an option. Though I do tend to get this merged into nix as nix has some great facilities for handling UNIX syscalls.

Are you intending to shut down the other one?

If nix wants it, I won't shut it down immediately, adding some deprecation messages to let users (if I have) migrate to nix would be the option.

[asomers]

Ok, but I don't have time to review it now. Postponing to the next release.

[asomers]

I just got back around to reviewing this, because I'm going to make a new release soon. I looked at your extattr crate, and I like it. In fact, I think I have another project that could benefit from it. However, Nix, as you may have noticed, has been getting rather bloated. And since you've already got this stuff wrapped up in a neatly self-contained crate, I propose that we keep it there rather than merge into Nix. Do you agree with that?

[SteveLauC]

I just got back around to reviewing this, because I'm going to make a new release soon.

Happy to hear that there will be a new release!

I propose that we keep it there rather than merge into Nix. Do you agree with that?

Yeah, Nix is indeed some kind of bloated, so i am ok with this proposal, I will close this PR.