mman MapFlags update for FreeBSD/NetBSD regarding page alignment

Related to page alignment, adding map_aligned for custom alignment
requirements.

changelog/2090.added.md

@@ -0,0 +1,2 @@
+Added `MAP_ALIGNMENT*` constants and `map_aligned` for NetBSD to `nix::sys::mman`.
+

src/sys/mman.rs

@@ -154,6 +154,36 @@ libc_bitflags! {
         /// Pages will be discarded in the core dumps.
         #[cfg(target_os = "openbsd")]
         MAP_CONCEAL;
+        /// Pages aligned on 64kb
+        #[cfg(target_os = "netbsd")]
+        #[cfg_attr(docsrs, doc(cfg(all())))]
+        MAP_ALIGNMENT_64KB;
+        /// Pages aligned on 16mb
+        #[cfg(target_os = "netbsd")]
+        #[cfg_attr(docsrs, doc(cfg(all())))]
+        MAP_ALIGNMENT_16MB;
+        /// Pages aligned on 4gb
+        #[cfg(target_os = "netbsd")]
+        #[cfg_attr(docsrs, doc(cfg(all())))]
+        MAP_ALIGNMENT_4GB;
+        /// Pages aligned on 1tb
+        #[cfg(target_os = "netbsd")]
+        #[cfg_attr(docsrs, doc(cfg(all())))]
+        MAP_ALIGNMENT_1TB;
+        /// Pages aligned on 256tb
+        #[cfg(target_os = "netbsd")]
+        #[cfg_attr(docsrs, doc(cfg(all())))]
+        MAP_ALIGNMENT_256TB;
+        /// Pages aligned on 64pb
+        #[cfg(target_os = "netbsd")]
+        #[cfg_attr(docsrs, doc(cfg(all())))]
+        MAP_ALIGNMENT_64PB;
+        /// Right operand value for the page alignment bitshift calculation
+        #[cfg(target_os = "netbsd")]
+        MAP_ALIGNMENT_SHIFT;
+        /// Mask to get the page alignment (as `(flags & align mask) >> align shift`)
+        #[cfg(target_os = "netbsd")]
+        MAP_ALIGNMENT_MASK;
     }
 }
 
@@ -631,3 +661,23 @@ pub fn shm_unlink<P: ?Sized + NixPath>(name: &P) -> Result<()> {
 
     Errno::result(ret).map(drop)
 }
+
+/// Matches BSD's `MAP_ALIGNED(x)` macro, x being ilog2(alignment).
+///
+/// For more information, see [`mmap(2)`].
+///
+/// [`mmap(2)`]: https://man.freebsd.org/cgi/man.cgi?mmap(2)
+#[cfg(target_os = "netbsd")]
+pub const fn map_aligned(v: u32) -> u32 {
+    v << MapFlags::MAP_ALIGNMENT_SHIFT.bits()
+}
+
+/// Handy call to get the alignment set by `map_aligned`.
+///
+/// For more information, see [`mmap(2)`].
+///
+/// [`mmap(2)`]: https://man.freebsd.org/cgi/man.cgi?mmap(2)
+#[cfg(target_os = "netbsd")]
+pub const fn map_alignment(flags: u32) -> u32 {
+    (flags & MapFlags::MAP_ALIGNMENT_MASK.bits() as u32) >> MapFlags::MAP_ALIGNMENT_SHIFT.bits()
+}

test/sys/test_mman.rs

@@ -119,3 +119,14 @@ fn test_mremap_shrink() {
     // The first KB should still be accessible and have the old data in it.
     assert_eq!(slice[ONE_K - 1], 0xFF);
 }
+
+#[test]
+#[cfg(target_os = "netbsd")]
+pub fn test_map_aligned() {
+    use nix::sys::mman::{map_aligned, map_alignment};
+
+    let aligned = map_aligned(16);
+    let flags = libc::MAP_PRIVATE as u32 | libc::MAP_ANONYMOUS as u32 | aligned;
+    assert_eq!(aligned, libc::MAP_ALIGNED(16) as u32);
+    assert_eq!(map_alignment(flags), 16);
+}