[pbs-devel] [PATCH proxmox v2] sys: file: use renameat2() from `nix` crate

[Thomas Lamprecht]

Am 12/07/2024 um 09:54 schrieb Christoph Heiss:
> Saves us from converting the paths to raw C strings ourselves, thus
> simplifying it quite a bit.
> 
> Since the `nix` crate does not provide link() directly, only linkat(),
> that is used instead - which behaves exactly the same as link() when
> using AT_FDCWD and an empty flag set.
> 
> No functional changes.
> 

OK by me in general, but I get the following errors on build (well `cargo check`):


```
    Checking proxmox-sys v0.6.0 (/root/sources/pbs/proxmox/proxmox-sys)
error[E0603]: struct `AtFlags` is private
   --> proxmox-sys/src/fs/file.rs:283:30
    |
283 |                 nix::unistd::AtFlags::empty(),
    |                              ^^^^^^^ private struct
    |
note: the struct `AtFlags` is defined here
   --> /usr/share/cargo/registry/nix-0.26.1/src/unistd.rs:6:30
    |
6   | use crate::fcntl::{at_rawfd, AtFlags};
    |                              ^^^^^^^
help: consider importing this struct instead
    |
283 |                 nix::fcntl::AtFlags::empty(),
    |                 ~~~~~~~~~~~~~~~~~~~
help: import `AtFlags` directly
    |
283 |                 nix::fcntl::AtFlags(),
    |                 ~~~~~~~~~~~~~~~~~~~

error[E0308]: mismatched types
    --> proxmox-sys/src/fs/file.rs:283:17
     |
278  |             let result = nix::unistd::linkat(
     |                          ------------------- arguments to this function are incorrect
...
283  |                 nix::unistd::AtFlags::empty(),
     |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `LinkatFlags`, found `AtFlags`
     |
note: function defined here
    --> /usr/share/cargo/registry/nix-0.26.1/src/unistd.rs:1252:8
     |
1252 | pub fn linkat<P: ?Sized + NixPath>(
     |        ^^^^^^

Some errors have detailed explanations: E0308, E0603.
For more information about an error, try `rustc --explain E0308`.
error: could not compile `proxmox-sys` (lib) due to 2 previous errors
```

Seems like you tested this with upstream nix, as the new type only works
since nix version 0.28, while we still got 0.26.1.

We might be able to upgrade nix, but that is often quite a bit more
involved.

Alternatively we could go with your v1 approach and apply

```
diff --git a/proxmox-sys/src/fs/file.rs b/proxmox-sys/src/fs/file.rs
index b2d6ddf6..28c7f88b 100644
--- a/proxmox-sys/src/fs/file.rs
+++ b/proxmox-sys/src/fs/file.rs
@@ -280,7 +280,7 @@ pub fn atomic_open_or_create_file<P: AsRef<Path>>(
                 &temp_file_name,
                 None,
                 &path.to_path_buf(),
-                nix::unistd::AtFlags::empty(),
+                nix::unistd::LinkatFlags::NoSymlinkFollow,
             );
             let _ = nix::unistd::unlink(&temp_file_name);
             result
```

On top for now.

Oh, please always test such changes with the crate versions provided by our
Debian package provided crate registry.