Expose mknodat and mkfifoat on Apple targets

Weak-link mknodat on Apple and return NOSYS when unavailable on older
systems. Keep direct libc calls on other targets.

Author: mattsu2020

src/backend/libc/fs/syscalls.rs

@@ -52,7 +52,6 @@ use crate::fs::StatFs;
 #[cfg(not(any(target_os = "espidf", target_os = "horizon", target_os = "vita")))]
 use crate::fs::Timestamps;
 #[cfg(not(any(
-    apple,
     target_os = "espidf",
     target_os = "horizon",
     target_os = "redox",
@@ -1206,7 +1205,6 @@ pub(crate) fn chownat(
 }
 
 #[cfg(not(any(
-    apple,
     target_os = "espidf",
     target_os = "horizon",
     target_os = "redox",
@@ -1220,13 +1218,30 @@ pub(crate) fn mknodat(
     mode: Mode,
     dev: Dev,
 ) -> io::Result<()> {
+    let dirfd = borrowed_fd(dirfd);
+    let pathname = c_str(path);
+    let mode = (mode.bits() | file_type.as_raw_mode()) as c::mode_t;
+    let dev = dev.try_into().map_err(|_e| io::Errno::PERM)?;
+
+    // Apple platforms before macOS 13.0, iOS 16.0, tvOS 16.0, and watchOS 9.0
+    // lack `mknodat`.
+    #[cfg(apple)]
     unsafe {
-        ret(c::mknodat(
-            borrowed_fd(dirfd),
-            c_str(path),
-            (mode.bits() | file_type.as_raw_mode()) as c::mode_t,
-            dev.try_into().map_err(|_e| io::Errno::PERM)?,
-        ))
+        weak! {
+            fn mknodat(
+                c::c_int,
+                *const ffi::c_char,
+                c::mode_t,
+                c::dev_t
+            ) -> c::c_int
+        }
+        let libc_mknodat = mknodat.get().ok_or(io::Errno::NOSYS)?;
+        ret(libc_mknodat(dirfd, pathname, mode, dev))
+    }
+
+    #[cfg(not(apple))]
+    unsafe {
+        ret(c::mknodat(dirfd, pathname, mode, dev))
     }
 }
 

src/fs/at.rs

@@ -21,7 +21,6 @@ use crate::fs::RenameFlags;
 #[cfg(not(target_os = "espidf"))]
 use crate::fs::Stat;
 #[cfg(not(any(
-    apple,
     target_os = "espidf",
     target_os = "horizon",
     target_os = "vita",
@@ -463,14 +462,21 @@ pub fn fclonefileat<Fd: AsFd, DstFd: AsFd, P: path::Arg>(
 
 /// `mknodat(dirfd, path, mode, dev)`—Creates special or normal files.
 ///
+/// # Platform support
+///
+/// On Apple platforms, this function requires macOS 13.0, iOS 16.0,
+/// tvOS 16.0, or watchOS 9.0 or later. On older versions, it returns
+/// [`io::Errno::NOSYS`].
+///
 /// # References
 ///  - [POSIX]
 ///  - [Linux]
+///  - [Apple]
 ///
 /// [POSIX]: https://pubs.opengroup.org/onlinepubs/9799919799/functions/mknodat.html
 /// [Linux]: https://man7.org/linux/man-pages/man2/mknodat.2.html
+/// [Apple]: https://github.com/apple-oss-distributions/xnu/blob/main/bsd/man/man2/mknodat.2
 #[cfg(not(any(
-    apple,
     target_os = "espidf",
     target_os = "horizon",
     target_os = "vita",
@@ -492,12 +498,19 @@ pub fn mknodat<P: path::Arg, Fd: AsFd>(
 
 /// `mkfifoat(dirfd, path, mode)`—Make a FIFO special file.
 ///
+/// # Platform support
+///
+/// On Apple platforms, this function requires macOS 13.0, iOS 16.0,
+/// tvOS 16.0, or watchOS 9.0 or later. On older versions, it returns
+/// [`io::Errno::NOSYS`].
+///
 /// # References
 ///  - [POSIX]
+///  - [Apple]
 ///
 /// [POSIX]: https://pubs.opengroup.org/onlinepubs/9799919799/functions/mkfifoat.html
+/// [Apple]: https://github.com/apple-oss-distributions/xnu/blob/main/bsd/man/man2/mkfifoat.2
 #[cfg(not(any(
-    apple,
     target_os = "espidf",
     target_os = "horizon",
     target_os = "vita",