Enable "std" feature on linux-raw-sys when "std" feature is enabled

[notgull]

As "std" changes API details from linux-raw-sys that is exposed in the public API, this would be a breaking change.

cc #753

[sdroege]

This currently means that xattr (1.1.0) and rustix can't be used in the same crate. xattr enables the std feature of linux-raw-sys, and rustix then fails compiling if also the net feature of rustix is enabled.

error[E0308]: mismatched types
  --> src/backend/linux_raw/net/addr.rs:39:32
   |
39 |             unix.sun_path[i] = *b;
   |             ----------------   ^^ expected `i8`, found `u8`
   |             |
   |             expected due to the type of this binding

error[E0308]: mismatched types
    --> src/backend/linux_raw/net/addr.rs:52:32
     |
52   |             id.copy_from_slice(name);
     |                --------------- ^^^^ expected `&[i8]`, found `&[u8]`
     |                |
     |                arguments to this method are incorrect
     |
     = note: expected reference `&[i8]`
                found reference `&[u8]`
[...]

[edulix]

I'm having this same issue. Our build suddently is broken:

error[E0308]: mismatched types
  --> /home/vscode/.cargo/registry/src/index.crates.io-6f17d22bba15001f/rustix-0.38.27/src/backend/linux_raw/net/addr.rs:39:32
   |
39 |             unix.sun_path[i] = *b;
   |             ----------------   ^^ expected `i8`, found `u8`
   |             |
   |             expected due to the type of this binding

error[E0308]: mismatched types
  --> /home/vscode/.cargo/registry/src/index.crates.io-6f17d22bba15001f/rustix-0.38.27/src/backend/linux_raw/net/addr.rs:52:32
   |
52 |             id.copy_from_slice(name);
   |                --------------- ^^^^ expected `&[i8]`, found `&[u8]`
   |                |
   |                arguments to this method are incorrect
   |
   = note: expected reference `&[i8]`
              found reference `&[u8]`
note: method defined here
  --> /rustc/9d871b0617a4b3d6610b7cee0ab5310dcb542c62/library/core/src/slice/mod.rs:3331:12

[edulix]

BTW Possible temporal quick and dirty fix: depend on rustix = "0.38.26" and it works. It got broken in a patch release..

[Stebalien]

xattr 1.1.1 has been released with a fix (reverts the change). I've yanked 1.1.0 now to prevent his from spreading.

[Stebalien]

(unless your issue is unrelated to xattr)

[sunfishcode]

I've now submitted #971 with a fix for this.

[sunfishcode]

#971 is now released in rustix 0.38.28.

[Tuupertunut]

I'm still getting compilation errors when adding xattr crate alongside rustix. It seems to change the definition of c_char from u8 to i8. Was this supposed to be fixed already?

[Stebalien]

@Tuupertunut what platform, what xattr version, and what rustix version?

[Tuupertunut]

Platform: stable-x86_64-unknown-linux-gnu, rustc 1.83.0

Dependencies before adding xattr:

[dependencies]
fuse_mt = "0.6.1"
fuser = "0.13.0"
ctrlc = { version = "3.4.5", features = ["termination"] }
rustix = { version = "0.38.43", features = ["fs"] }

[dev-dependencies]
tempfile = "3.15.0"

rustix::fs::listxattr() takes in &mut [linux_raw_sys::ctypes::c_char] = &mut [u8]

After adding xattr:

[dependencies]
fuse_mt = "0.6.1"
fuser = "0.13.0"
ctrlc = { version = "3.4.5", features = ["termination"] }
rustix = { version = "0.38.43", features = ["fs"] }
xattr = "1.4.0"

[dev-dependencies]
tempfile = "3.15.0"

rustix::fs::listxattr() takes in &mut [core::ffi::c_char] = &mut [i8]

[Stebalien]

Can you post the compilation error?

[Stebalien]

Does Stebalien/xattr#70 work? You can patch it in with (untested, but it should work...):

[patch.crates-io]
xattr = { git = "https://github.com/Stebalien/xattr", branch = "steb/use-rustix-c-char" }

[Tuupertunut]

Can you post the compilation error?

The compilation error is simply a type mismatch

error[E0308]: mismatched types
   --> src/overlayfs.rs:803:56
    |
803 |                     rustix::fs::llistxattr(layer_path, &mut buffer).err_to_errno()?;
    |                     ----------------------             ^^^^^^^^^^^ expected `&mut [i8]`, found `&mut Vec<u8>`
    |                     |
    |                     arguments to this function are incorrect
    |
    = note: expected mutable reference `&mut [i8]`
               found mutable reference `&mut Vec<u8>`

Does Stebalien/xattr#70 work?

No, it shows the same compilation error. Thank you for your help in debugging this issue.

Now I'm just wondering two things:

• Why is xattr enabling the "std" feature of linux-raw-sys (here)? This seems to cause the problem for me as rustix does not have the "std" feature of linux-raw-sys enabled, but when I add xattr as dependency, it turns that feature on and the definition of c_char changes for existing rustix code.

• Why is rustix using c_char to represent characters in listxattr() when in Rust CString is usually considered to consist of u8s? (In fact that's the definition of Rust CString) Could it be changed to take in &mut [u8]? This has been requested also in Painful [i8] in rustix::fs::listxattr() #1218.

[Stebalien]

Everything breaks without the rustix "std" feature (wrong error types, issues with string conversions, etc.). xattr itself requires the standard library so there's no real benefit to supporting no-std (and it's not supposed to have any other knock-on effects).

It sounds like this bug wasn't actually fixed. xattr shouldn't actually depend on linux-raw-sys and, as you say, shouldn't enable the "std" feature there. But, if I don't enable that feature, rustix becomes incompatible with stdlib CStr, so that's a non-starter.

[Stebalien]

Ok, I still think this issue should be fixed (enabling "std" in rustix should enable "std" in linux-raw-sys), but the real issue here is #1261.