From 30e1162d7cee505aeac8a3711787aa23cf784a34 Mon Sep 17 00:00:00 2001
From: Sebastien Boeuf <sebastien.boeuf@intel.com>
Date: Wed, 7 Oct 2020 12:20:30 +0200
Subject: [PATCH] virtio: Replace some repr(C, packed) with repr(C)

The goal here is to replace anywhere possible a virtio structure
with a "C, packed" representation by a "C" representation. Some
virtio structures are not expected to be packed, therefore there's
no reason for using the more restrictive "C, packed" representation.

This is important since "packed" representation can still cause
undefined behaviors with Rust 2018.

By removing the need for "packed" representation, we can simplify a
bit of code by deriving the Serialize trait without writing the
implementation ourselves.

Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>
---
 virtio-devices/src/mem.rs  |  2 +-
 virtio-devices/src/pmem.rs | 25 ++-----------------------
 2 files changed, 3 insertions(+), 24 deletions(-)

diff --git a/virtio-devices/src/mem.rs b/virtio-devices/src/mem.rs
index 673688e77..31e620c19 100644
--- a/virtio-devices/src/mem.rs
+++ b/virtio-devices/src/mem.rs
@@ -159,7 +159,7 @@ struct VirtioMemResp {
 unsafe impl ByteValued for VirtioMemResp {}
 
 // Got from qemu/include/standard-headers/linux/virtio_mem.h
-#[repr(C, packed)]
+#[repr(C)]
 #[derive(Copy, Clone, Debug, Default)]
 struct VirtioMemConfig {
     // Block size and alignment. Cannot change.
diff --git a/virtio-devices/src/pmem.rs b/virtio-devices/src/pmem.rs
index d64f2c584..a165faa43 100644
--- a/virtio-devices/src/pmem.rs
+++ b/virtio-devices/src/pmem.rs
@@ -16,7 +16,6 @@ use crate::seccomp_filters::{get_seccomp_filter, Thread};
 use crate::{VirtioInterrupt, VirtioInterruptType};
 use anyhow::anyhow;
 use seccomp::{SeccompAction, SeccompFilter};
-use serde::ser::{Serialize, SerializeStruct, Serializer};
 use std::fmt::{self, Display};
 use std::fs::File;
 use std::io;
@@ -46,33 +45,13 @@ const VIRTIO_PMEM_RESP_TYPE_EIO: u32 = 1;
 // New descriptors are pending on the virtio queue.
 const QUEUE_AVAIL_EVENT: u16 = EPOLL_HELPER_EVENT_LAST + 1;
 
-#[derive(Copy, Clone, Debug, Default, Deserialize)]
-#[repr(C, packed)]
+#[derive(Copy, Clone, Debug, Default, Serialize, Deserialize)]
+#[repr(C)]
 struct VirtioPmemConfig {
     start: u64,
     size: u64,
 }
 
-// We must explicitly implement Serialize since the structure is packed and
-// it's unsafe to borrow from a packed structure. And by default, if we derive
-// Serialize from serde, it will borrow the values from the structure.
-// That's why this implementation copies each field separately before it
-// serializes the entire structure field by field.
-impl Serialize for VirtioPmemConfig {
-    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
-    where
-        S: Serializer,
-    {
-        let start = self.start;
-        let size = self.size;
-
-        let mut virtio_pmem_config = serializer.serialize_struct("VirtioPmemConfig", 16)?;
-        virtio_pmem_config.serialize_field("start", &start)?;
-        virtio_pmem_config.serialize_field("size", &size)?;
-        virtio_pmem_config.end()
-    }
-}
-
 // Safe because it only has data and has no implicit padding.
 unsafe impl ByteValued for VirtioPmemConfig {}