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data_model: Implement Send + Sync for IoSliceMut

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Pointers in rust don't implement Send or Sync and so any struct that
contains a raw pointer doesn't implement those traits either.  However,
there's nothing inherently unsafe about sending a pointer across thread
boundaries.  The only unsafety comes from actually de-referencing the
pointer, which already requires an unsafe block.

Explicitly implement Send + Sync for IoSliceMut since the iovec
internally holds a *mut c_void, which prevents those traits from being
auto-implemented.  Send + Sync is also implemented by
std::io::IoSliceMut, which is almost exactly the same as our IoSliceMut,
so that can provide some additional reassurance that this is safe.

Also add a missing copyright header in the file.

BUG=none
TEST=unit tests

Change-Id: Ic21fc0de9b29923420f36ab166fec80d4d4cf2e3
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/2571146
Reviewed-by: Noah Gold <nkgold@google.com>
Reviewed-by: Dylan Reid <dgreid@chromium.org>
Tested-by: kokoro <noreply+kokoro@google.com>
Commit-Queue: Chirantan Ekbote <chirantan@chromium.org>
This commit is contained in:
Chirantan Ekbote 2020-11-30 17:14:49 +09:00 committed by Commit Bot
parent 0a086e6cbe
commit f1444aaf72
1 changed files with 11 additions and 0 deletions
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11
data_model/src/sys.rs
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@ -1,3 +1,7 @@
// Copyright 2020 The Chromium OS Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
use std::ffi::c_void; use std::ffi::c_void;
use std::fmt::{self, Debug}; use std::fmt::{self, Debug};
use std::marker::PhantomData; use std::marker::PhantomData;
@ -70,6 +74,13 @@ impl<'a> IoSliceMut<'a> {
} }
} }
// It's safe to implement Send + Sync for this type for the same reason that `std::io::IoSliceMut`
// is Send + Sync. Internally, it contains a pointer and a length. The integer length is safely Send
// + Sync. There's nothing wrong with sending a pointer between threads and de-referencing the
// pointer requires an unsafe block anyway. See also https://github.com/rust-lang/rust/pull/70342.
unsafe impl<'a> Send for IoSliceMut<'a> {}
unsafe impl<'a> Sync for IoSliceMut<'a> {}
struct DebugIovec(iovec); struct DebugIovec(iovec);
impl Debug for DebugIovec { impl Debug for DebugIovec {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {