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[Qemu-devel] [PATCH 2/2] vhost-user: fix misaligned access to payload
From: |
Michael S. Tsirkin |
Subject: |
[Qemu-devel] [PATCH 2/2] vhost-user: fix misaligned access to payload |
Date: |
Mon, 8 Jan 2018 19:50:44 +0200 |
We currently take a pointer to a misaligned field of a packed structure.
clang reports this as a build warning.
A fix is to keep payload in a separate structure, and access is it
from there using a vectored write.
Signed-off-by: Michael S. Tsirkin <address@hidden>
---
hw/virtio/vhost-user.c | 39 ++++++++++++++++++++++++---------------
1 file changed, 24 insertions(+), 15 deletions(-)
diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
index e2477a1..a9a251e 100644
--- a/hw/virtio/vhost-user.c
+++ b/hw/virtio/vhost-user.c
@@ -616,33 +616,34 @@ static void slave_read(void *opaque)
{
struct vhost_dev *dev = opaque;
struct vhost_user *u = dev->opaque;
- VhostUserMsg msg = { 0, };
+ VhostUserHeader hdr = { 0, };
+ VhostUserPayload payload = { 0, };
int size, ret = 0;
/* Read header */
- size = read(u->slave_fd, &msg, VHOST_USER_HDR_SIZE);
+ size = read(u->slave_fd, &hdr, VHOST_USER_HDR_SIZE);
if (size != VHOST_USER_HDR_SIZE) {
error_report("Failed to read from slave.");
goto err;
}
- if (msg.hdr.size > VHOST_USER_PAYLOAD_SIZE) {
+ if (hdr.size > VHOST_USER_PAYLOAD_SIZE) {
error_report("Failed to read msg header."
- " Size %d exceeds the maximum %zu.", msg.hdr.size,
+ " Size %d exceeds the maximum %zu.", hdr.size,
VHOST_USER_PAYLOAD_SIZE);
goto err;
}
/* Read payload */
- size = read(u->slave_fd, &msg.payload, msg.hdr.size);
- if (size != msg.hdr.size) {
+ size = read(u->slave_fd, &payload, hdr.size);
+ if (size != hdr.size) {
error_report("Failed to read payload from slave.");
goto err;
}
- switch (msg.hdr.request) {
+ switch (hdr.request) {
case VHOST_USER_SLAVE_IOTLB_MSG:
- ret = vhost_backend_handle_iotlb_msg(dev, &msg.payload.iotlb);
+ ret = vhost_backend_handle_iotlb_msg(dev, &payload.iotlb);
break;
default:
error_report("Received unexpected msg type.");
@@ -653,15 +654,23 @@ static void slave_read(void *opaque)
* REPLY_ACK feature handling. Other reply types has to be managed
* directly in their request handlers.
*/
- if (msg.hdr.flags & VHOST_USER_NEED_REPLY_MASK) {
- msg.hdr.flags &= ~VHOST_USER_NEED_REPLY_MASK;
- msg.hdr.flags |= VHOST_USER_REPLY_MASK;
+ if (hdr.flags & VHOST_USER_NEED_REPLY_MASK) {
+ struct iovec iovec[2];
- msg.payload.u64 = !!ret;
- msg.hdr.size = sizeof(msg.payload.u64);
- size = write(u->slave_fd, &msg, VHOST_USER_HDR_SIZE + msg.hdr.size);
- if (size != VHOST_USER_HDR_SIZE + msg.hdr.size) {
+ hdr.flags &= ~VHOST_USER_NEED_REPLY_MASK;
+ hdr.flags |= VHOST_USER_REPLY_MASK;
+
+ payload.u64 = !!ret;
+ hdr.size = sizeof(payload.u64);
+
+ iovec[0].iov_base = &hdr;
+ iovec[0].iov_len = VHOST_USER_HDR_SIZE;
+ iovec[1].iov_base = &payload;
+ iovec[1].iov_len = hdr.size;
+
+ size = writev(u->slave_fd, iovec, ARRAY_SIZE(iovec));
+ if (size != VHOST_USER_HDR_SIZE + hdr.size) {
error_report("Failed to send msg reply to slave.");
goto err;
}
--
MST