Add mmap_anonymous function

Author: newpavlov

src/sys/mman.rs

@@ -426,8 +426,7 @@ pub unsafe fn mmap<F: AsFd>(
     f: Option<F>,
     offset: off_t,
 ) -> Result<*mut c_void> {
-    let ptr =
-        addr.map_or(std::ptr::null_mut(), |a| usize::from(a) as *mut c_void);
+    let ptr = addr.map_or(std::ptr::null_mut(), |a| a.get() as *mut c_void);
 
     let fd = f.map(|f| f.as_fd().as_raw_fd()).unwrap_or(-1);
     let ret =
@@ -440,6 +439,34 @@ pub unsafe fn mmap<F: AsFd>(
     }
 }
 
+/// Create an anonymous memory mapping.
+///
+/// This function is a wrapper around [`mmap`]:
+/// `mmap(ptr, len, prot, MAP_ANONYMOUS | flags, -1, 0)`.
+///
+/// # Safety
+///
+/// See the [`mmap(2)`] man page for detailed requirements.
+///
+/// [`mmap(2)`]: https://man7.org/linux/man-pages/man2/mmap.2.html
+pub unsafe fn mmap_anonymous(
+    addr: Option<NonZeroUsize>,
+    length: NonZeroUsize,
+    prot: ProtFlags,
+    flags: MapFlags,
+) -> Result<*mut c_void> {
+    let ptr = addr.map_or(std::ptr::null_mut(), |a| a.get() as *mut c_void);
+
+    let flags = MapFlags::MAP_ANONYMOUS | flags;
+    let ret = libc::mmap(ptr, length.into(), prot.bits(), flags.bits(), -1, 0);
+
+    if ret == libc::MAP_FAILED {
+        Err(Errno::last())
+    } else {
+        Ok(ret)
+    }
+}
+
 /// Expands (or shrinks) an existing memory mapping, potentially moving it at
 /// the same time.
 ///