Re: [PATCH v2] vhost: fix external message handlers

[Christophe Fontaine <cfontain@redhat.com>]

On Tue, Mar 8, 2022 at 10:44 AM David Marchand
<david.marchand@redhat.com> wrote:
>
> Following a rework, external message handlers were receiving a pointer
> to a vhost_user message (as stated in the API), but lost the ability to
> interact with fds attached to the message.
> Restore the original layout and put a build check and reminders.
>
> Bugzilla ID: 953
> Fixes: 5e0099dc709e ("vhost: remove payload size limitation")
>
> Reported-by: Fan Zhang <roy.fan.zhang@intel.com>
> Signed-off-by: David Marchand <david.marchand@redhat.com>
> ---
> Changes since v1:
> - fixed build with clang,
>
> ---
>  lib/vhost/vhost_user.c | 8 ++++----
>  lib/vhost/vhost_user.h | 7 +++++--
>  2 files changed, 9 insertions(+), 6 deletions(-)
>
> diff --git a/lib/vhost/vhost_user.c b/lib/vhost/vhost_user.c
> index 723c6890c3..589b950458 100644
> --- a/lib/vhost/vhost_user.c
> +++ b/lib/vhost/vhost_user.c
> @@ -3023,8 +3023,8 @@ vhost_user_msg_handler(int vid, int fd)
>
>         handled = false;
>         if (dev->extern_ops.pre_msg_handle) {
> -               ret = (*dev->extern_ops.pre_msg_handle)(dev->vid,
> -                               (void *)&ctx.msg);
> +               RTE_BUILD_BUG_ON(offsetof(struct vhu_msg_context, msg) != 0);
> +               ret = (*dev->extern_ops.pre_msg_handle)(dev->vid, &ctx);
>                 switch (ret) {
>                 case RTE_VHOST_MSG_RESULT_REPLY:
>                         send_vhost_reply(dev, fd, &ctx);
> @@ -3069,8 +3069,8 @@ vhost_user_msg_handler(int vid, int fd)
>  skip_to_post_handle:
>         if (ret != RTE_VHOST_MSG_RESULT_ERR &&
>                         dev->extern_ops.post_msg_handle) {
> -               ret = (*dev->extern_ops.post_msg_handle)(dev->vid,
> -                               (void *)&ctx.msg);
> +               RTE_BUILD_BUG_ON(offsetof(struct vhu_msg_context, msg) != 0);
> +               ret = (*dev->extern_ops.post_msg_handle)(dev->vid, &ctx);
>                 switch (ret) {
>                 case RTE_VHOST_MSG_RESULT_REPLY:
>                         send_vhost_reply(dev, fd, &ctx);
> diff --git a/lib/vhost/vhost_user.h b/lib/vhost/vhost_user.h
> index be53669f3b..c946cc2ef4 100644
> --- a/lib/vhost/vhost_user.h
> +++ b/lib/vhost/vhost_user.h
> @@ -152,10 +152,13 @@ typedef struct VhostUserMsg {
>         /* Nothing should be added after the payload */
>  } __rte_packed VhostUserMsg;
>
> -struct vhu_msg_context {
> +/* Note: this structure and VhostUserMsg can't be changed carelessly as
> + * external message handlers rely on them.
> + */
> +struct __rte_packed vhu_msg_context {
> +       VhostUserMsg msg;
>         int fds[VHOST_MEMORY_MAX_NREGIONS];
>         int fd_num;
> -       VhostUserMsg msg;
>  };
>
>  #define VHOST_USER_HDR_SIZE offsetof(VhostUserMsg, payload.u64)
> --
> 2.23.0
>

Sorry to have missed that test with virtio-crypto ; I'll create
another thread to talk about the VhostUserMsg extension.

Reviewed-by: Christophe Fontaine <cfontain@redhat.com>

Thanks,
Christophe