sys_util: Refactor IntoIovec

The original stated purpose of this trait was to reduce memory
allocations but having the `into_iovec` method return a Vec kind of
defeats that purpose.

Refactor the trait so that it can either convert a T into an iovec or
convert a &[T] into a &[iovec].  Implement the trait for VolatileSlice,
IoSlice, and IoSliceMut and update all the callers.

BUG=none
TEST=unit tests

Cq-Depend: chromium:2210272
Change-Id: I9d0d617a23030d241d50411f4a5a16e7cba4bcee
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/2208527
Reviewed-by: Daniel Verkamp <dverkamp@chromium.org>
Reviewed-by: Zach Reizner <zachr@chromium.org>
Commit-Queue: Chirantan Ekbote <chirantan@chromium.org>
Tested-by: Chirantan Ekbote <chirantan@chromium.org>

1 files changed, 3 insertions, 2 deletions

diff --git a/msg_socket/src/lib.rs b/msg_socket/src/lib.rs
index 7f5d1a6..540d49d 100644
--- a/msg_socket/src/lib.rs
+++ b/msg_socket/src/lib.rs
@@ -4,7 +4,7 @@
 
 mod msg_on_socket;
 
-use std::io::Result;
+use std::io::{IoSlice, Result};
 use std::marker::PhantomData;
 use std::os::unix::io::{AsRawFd, RawFd};
 use std::pin::Pin;
@@ -138,7 +138,8 @@ pub trait MsgSender: AsRef<UnixSeqpacket> {
             handle_eintr!(sock.send(&msg_buffer))
                 .map_err(|e| MsgError::Send(SysError::new(e.raw_os_error().unwrap_or(0))))?;
         } else {
-            sock.send_with_fds(&msg_buffer[..], &fd_buffer[0..fd_size])
+            let ioslice = IoSlice::new(&msg_buffer[..]);
+            sock.send_with_fds(&[ioslice], &fd_buffer[0..fd_size])
                 .map_err(MsgError::Send)?;
         }
         Ok(())