Add nonblock.rs

zenith_utils/src/nonblock.rs

@@ -0,0 +1,17 @@
+use nix::fcntl::{fcntl, OFlag, F_GETFL, F_SETFL};
+use std::os::unix::io::RawFd;
+
+/// Put a file descriptor into non-blocking mode
+pub fn set_nonblock(fd: RawFd) -> Result<(), std::io::Error> {
+    let bits = fcntl(fd, F_GETFL)?;
+
+    // Safety: If F_GETFL returns some unknown bits, they should be valid
+    // for passing back to F_SETFL, too. If we left them out, the F_SETFL
+    // would effectively clear them, which is not what we want.
+    let mut flags = unsafe { OFlag::from_bits_unchecked(bits) };
+    flags |= OFlag::O_NONBLOCK;
+
+    fcntl(fd, F_SETFL(flags))?;
+
+    Ok(())
+}