libopenbsd.rs(3): fixes API for unveil(2)

src/libopenbsd.rs

@@ -17,7 +17,7 @@
  */
 
 use std::{
-	ffi::{ CString, c_int },
+	ffi::CString,
 	io::Error,
 	ptr::null,
 };
@@ -76,7 +76,10 @@ impl UnveilPerms {
 	}
 }
 
-pub fn unveil(path: Option<&str>, permissions: Option<UnveilPerms>) -> c_int {
+pub fn unveil(
+	path: Option<&str>,
+	permissions: Option<UnveilPerms>,
+) -> Result<(), Error> {
 	let path_c = path.map(CString::new).map(Result::unwrap);
 	let arg1 = path_c.map(|p| p.into_raw() as *const i8).unwrap_or(null());
 
@@ -84,5 +87,11 @@ pub fn unveil(path: Option<&str>, permissions: Option<UnveilPerms>) -> c_int {
 		.map(|p| p.0.into_raw() as *const i8)
 		.unwrap_or(null());
 
-	unsafe { openbsd::unveil(arg1, arg2) }
+	unsafe {
+		match openbsd::unveil(arg1, arg2) {
+			-1 => Err(Error::from_raw_os_error(*openbsd::__errno())),
+			0 => Ok(()),
+			_ => panic!(), /* unreachable */
+		}
+	}
 }