add docs for pack_mhdr_to_receive

Author: pacak

src/sys/socket/mod.rs

@@ -1844,6 +1844,17 @@ unsafe fn read_mhdr<'a, S>(
     }
 }
 
+/// Pack pointers to various structures into into msghdr
+///
+/// # Safety
+/// `iov_buffer` and `iov_buffer_len` must point to a slice
+/// of `IoSliceMut` and number of available elements or be a null pointer and 0
+///
+/// `cmsg_buffer` and `cmsg_capacity` must point to a byte buffer used
+/// to store control headers later or be a null pointer and 0 if control
+/// headers are not used
+///
+/// Buffers must remain valid for the whole lifetime of msghdr
 unsafe fn pack_mhdr_to_receive<S>(
     iov_buffer: *const IoSliceMut,
     iov_buffer_len: usize,