Updated the docs for preadv and pwritev

Author: simlay

library/std/src/sys/pal/unix/fd.rs

@@ -250,13 +250,15 @@ impl FileDesc {
         }
     }
 
-    // We support old MacOS, iOS, watchOS, tvOS and visionOS versions that do not have `preadv`.
-    // There is no `syscall` possible in these platform for following apple versions:
+    // We support old MacOS, iOS, watchOS, tvOS and visionOS. `preadv` was added in the following
+    // Apple OS versions:
     // ios 14.0
     // tvos 14.0
     // macos 11.0
     // watchos 7.0
-    // visionos 1.0
+    //
+    // These versions may be newer than the minimum supported versions of OS's we support so we must
+    // use "weak" linking.
     #[cfg(target_vendor = "apple")]
     pub fn read_vectored_at(&self, bufs: &mut [IoSliceMut<'_>], offset: u64) -> io::Result<usize> {
         super::weak::weak!(fn preadv(libc::c_int, *const libc::iovec, libc::c_int, off64_t) -> isize);
@@ -425,13 +427,15 @@ impl FileDesc {
         }
     }
 
-    // We support old MacOS, iOS, watchOS, tvOS and visionOS versions that do not have `pwritev`.
-    // There is no `syscall` possible in these platform for following apple versions:
+    // We support old MacOS, iOS, watchOS, tvOS and visionOS. `pwritev` was added in the following
+    // Apple OS versions:
     // ios 14.0
     // tvos 14.0
     // macos 11.0
     // watchos 7.0
-    // visionos 1.0
+    //
+    // These versions may be newer than the minimum supported versions of OS's we support so we must
+    // use "weak" linking.
     #[cfg(target_vendor = "apple")]
     pub fn write_vectored_at(&self, bufs: &[IoSlice<'_>], offset: u64) -> io::Result<usize> {
         super::weak::weak!(fn pwritev(libc::c_int, *const libc::iovec, libc::c_int, off64_t) -> isize);