netbsd: Clarify type conversions are lossless.

Author: briansmith

src/netbsd.rs

@@ -1,13 +1,14 @@
 //! Implementation for NetBSD
 use crate::{lazy::LazyPtr, util_libc::sys_fill_exact, Error};
-use core::{ffi::c_void, mem::MaybeUninit, ptr};
+use core::{cmp, ffi::c_void, mem::MaybeUninit, ptr};
 
 fn kern_arnd(buf: &mut [MaybeUninit<u8>]) -> libc::ssize_t {
     static MIB: [libc::c_int; 2] = [libc::CTL_KERN, libc::KERN_ARND];
-    let mut len = buf.len();
+    let mut len = cmp::min(len, libc::ssize_t::MAX.unsignd_abs());
     let ret = unsafe {
         libc::sysctl(
             MIB.as_ptr(),
+            #[allow(clippy::cast_possible_truncation)]
             MIB.len() as libc::c_uint,
             buf.as_mut_ptr().cast::<c_void>(),
             &mut len,
@@ -18,7 +19,10 @@ fn kern_arnd(buf: &mut [MaybeUninit<u8>]) -> libc::ssize_t {
     if ret == -1 {
         -1
     } else {
-        len as libc::ssize_t
+        // We clamped the request to `ssize_t::MAX` bytes so this lossless.
+        #[allow(clippy::cast_possible_truncation)]
+        let len = len as libc::ssize_t;
+        len
     }
 }