diff --git a/net_util/src/tap.rs b/net_util/src/tap.rs
index 6d90293b8..533d6a45b 100644
--- a/net_util/src/tap.rs
+++ b/net_util/src/tap.rs
@@ -129,6 +129,9 @@ fn ipv6_mask_to_prefix(mask: Ipv6Addr) -> Result<u8> {
 }
 
 impl Tap {
+    /// # Safety
+    /// The caller should ensure to pass a valid file descriptor and valid
+    /// arguments for the `ioctl()` syscall.
     unsafe fn ioctl_with_mut_ref<F: AsRawFd, T>(fd: &F, req: c_ulong, arg: &mut T) -> Result<()> {
         let ret = ioctl_with_mut_ref(fd, req, arg);
         if ret < 0 {
@@ -138,6 +141,9 @@ impl Tap {
         Ok(())
     }
 
+    /// # Safety
+    /// The caller should ensure to pass a valid file descriptor and valid
+    /// arguments for the `ioctl()` syscall.
     unsafe fn ioctl_with_ref<F: AsRawFd, T>(fd: &F, req: c_ulong, arg: &T) -> Result<()> {
         let ret = ioctl_with_ref(fd, req, arg);
         if ret < 0 {
@@ -147,6 +153,9 @@ impl Tap {
         Ok(())
     }
 
+    /// # Safety
+    /// The caller should ensure to pass a valid file descriptor and valid
+    /// arguments for the `ioctl()` syscall.
     unsafe fn ioctl_with_val<F: AsRawFd>(fd: &F, req: c_ulong, arg: c_ulong) -> Result<()> {
         let ret = ioctl_with_val(fd, req, arg);
         if ret < 0 {
diff --git a/vmm/src/clone3.rs b/vmm/src/clone3.rs
index f08e5ad31..0ab08126e 100644
--- a/vmm/src/clone3.rs
+++ b/vmm/src/clone3.rs
@@ -22,6 +22,16 @@ pub struct clone_args {
     pub cgroup: u64,
 }
 
+/// # Safety
+/// `size` must have the proper size to match `args`.
+/// Further, the caller needs to check the return value.
+///
+/// # Return
+/// - On success:
+///   - Parent: child PID (`c_long`)
+///   - Child: `0`
+/// - On error: `-1` and `errno` is set
+#[must_use]
 pub unsafe fn clone3(args: &mut clone_args, size: size_t) -> c_long {
     syscall(SYS_clone3, args, size)
 }