feat: mmap NonNull

CHANGELOG.md

@@ -33,6 +33,9 @@ This project adheres to [Semantic Versioning](https://semver.org/).
   relaxed lifetime requirements relative to 0.27.1.
   ([#2136](https://github.com/nix-rust/nix/pull/2136))
 
+- `sys::mman::mmap` to return `NonNull<c_void>`.
+  ([#2000](https://github.com/nix-rust/nix/pull/2000))
+
 ## [0.27.1] - 2023-08-28
 
 ### Fixed
@@ -114,6 +117,9 @@ This project adheres to [Semantic Versioning](https://semver.org/).
   `sys::kevent::Kqueue::kevent`, and `sys::event::kqueue` is deprecated in
   favor of `sys::kevent::Kqueue::new`.
   ([#1943](https://github.com/nix-rust/nix/pull/1943))
+
+### Removed
+
 - Removed deprecated IoVec API.
   ([#1855](https://github.com/nix-rust/nix/pull/1855))
 - Removed deprecated net APIs.

src/sys/mman.rs

@@ -9,6 +9,7 @@ use crate::Result;
 use crate::{fcntl::OFlag, sys::stat::Mode};
 use libc::{self, c_int, c_void, off_t, size_t};
 use std::{num::NonZeroUsize, os::unix::io::{AsRawFd, AsFd}};
+use std::ptr::NonNull;
 
 libc_bitflags! {
     /// Desired memory protection of a memory mapping.
@@ -425,19 +426,15 @@ pub unsafe fn mmap<F: AsFd>(
     flags: MapFlags,
     f: Option<F>,
     offset: off_t,
-) -> Result<*mut c_void> {
+) -> Result<NonNull<c_void>> {
     let ptr =
         addr.map_or(std::ptr::null_mut(), |a| usize::from(a) as *mut c_void);
 
     let fd = f.map(|f| f.as_fd().as_raw_fd()).unwrap_or(-1);
     let ret =
         libc::mmap(ptr, length.into(), prot.bits(), flags.bits(), fd, offset);
-
-    if ret == libc::MAP_FAILED {
-        Err(Errno::last())
-    } else {
-        Ok(ret)
-    }
+
+    NonNull::new(ret).ok_or_else(Errno::last)
 }
 
 /// Expands (or shrinks) an existing memory mapping, potentially moving it at
@@ -527,8 +524,8 @@ pub unsafe fn madvise(
 /// let mut slice: &mut [u8] = unsafe {
 ///     let mem = mmap::<BorrowedFd>(None, one_k_non_zero, ProtFlags::PROT_NONE,
 ///                    MapFlags::MAP_ANON | MapFlags::MAP_PRIVATE, None, 0).unwrap();
-///     mprotect(mem, ONE_K, ProtFlags::PROT_READ | ProtFlags::PROT_WRITE).unwrap();
-///     std::slice::from_raw_parts_mut(mem as *mut u8, ONE_K)
+///     mprotect(mem.as_ptr(), ONE_K, ProtFlags::PROT_READ | ProtFlags::PROT_WRITE).unwrap();
+///     std::slice::from_raw_parts_mut(mem.as_ptr().cast(), ONE_K)
 /// };
 /// assert_eq!(slice[0], 0x00);
 /// slice[0] = 0xFF;

test/sys/test_mman.rs

@@ -4,18 +4,19 @@ use std::{num::NonZeroUsize, os::unix::io::BorrowedFd};
 #[test]
 fn test_mmap_anonymous() {
     unsafe {
-        let ptr = mmap::<BorrowedFd>(
+        let mut ptr = mmap::<BorrowedFd>(
             None,
             NonZeroUsize::new(1).unwrap(),
             ProtFlags::PROT_READ | ProtFlags::PROT_WRITE,
             MapFlags::MAP_PRIVATE | MapFlags::MAP_ANONYMOUS,
             None,
             0,
         )
-        .unwrap() as *mut u8;
-        assert_eq!(*ptr, 0x00u8);
-        *ptr = 0xffu8;
-        assert_eq!(*ptr, 0xffu8);
+        .unwrap()
+        .cast::<u8>();
+        assert_eq!(*ptr.as_ref(), 0x00u8);
+        *ptr.as_mut() = 0xffu8;
+        assert_eq!(*ptr.as_ref(), 0xffu8);
     }
 }
 
@@ -38,7 +39,7 @@ fn test_mremap_grow() {
             0,
         )
         .unwrap();
-        std::slice::from_raw_parts_mut(mem as *mut u8, ONE_K)
+        std::slice::from_raw_parts_mut(mem.as_ptr().cast(), ONE_K)
     };
     assert_eq!(slice[ONE_K - 1], 0x00);
     slice[ONE_K - 1] = 0xFF;
@@ -96,7 +97,7 @@ fn test_mremap_shrink() {
             0,
         )
         .unwrap();
-        std::slice::from_raw_parts_mut(mem as *mut u8, ONE_K)
+        std::slice::from_raw_parts_mut(mem.as_ptr().cast(), ONE_K)
     };
     assert_eq!(slice[ONE_K - 1], 0x00);
     slice[ONE_K - 1] = 0xFF;