Re: [PATCH v2 26/29] hw/virtio/vhost: Fix missing ERRP_GUARD() for error_prepend()

[Thomas Huth <thuth@redhat.com>]

On 11/03/2024 04.38, Zhao Liu wrote:
> From: Zhao Liu <zhao1.liu@intel.com>
> 
> As the comment in qapi/error, passing @errp to error_prepend() requires
> ERRP_GUARD():
> 
> * = Why, when and how to use ERRP_GUARD() =
> *
> * Without ERRP_GUARD(), use of the @errp parameter is restricted:
> ...
> * - It should not be passed to error_prepend(), error_vprepend() or
> *   error_append_hint(), because that doesn't work with &error_fatal.
> * ERRP_GUARD() lifts these restrictions.
> *
> * To use ERRP_GUARD(), add it right at the beginning of the function.
> * @errp can then be used without worrying about the argument being
> * NULL or &error_fatal.
> 
> ERRP_GUARD() could avoid the case when @errp is &error_fatal, the user
> can't see this additional information, because exit() happens in
> error_setg earlier than information is added [1].
> 
> In hw/virtio/vhost.c, there are 2 functions passing @errp to
> error_prepend() without ERRP_GUARD():
> - vhost_save_backend_state()
> - vhost_load_backend_state()
> 
> Their @errp both points to callers' @local_err. However, as the APIs
> defined in include/hw/virtio/vhost.h, it is necessary to protect their
> @errp with ERRP_GUARD().
> 
> To follow the requirement of @errp, add missing ERRP_GUARD() at their
> beginning.
> 
> [1]: Issue description in the commit message of commit ae7c80a7bd73
>       ("error: New macro ERRP_GUARD()").
> 
> Cc: "Michael S. Tsirkin" <mst@redhat.com>
> Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
> ---
>   hw/virtio/vhost.c | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
> index 2c9ac794680e..2e4e040db87a 100644
> --- a/hw/virtio/vhost.c
> +++ b/hw/virtio/vhost.c
> @@ -2199,6 +2199,7 @@ int vhost_check_device_state(struct vhost_dev *dev, Error **errp)
>   
>   int vhost_save_backend_state(struct vhost_dev *dev, QEMUFile *f, Error **errp)
>   {
> +    ERRP_GUARD();
>       /* Maximum chunk size in which to transfer the state */
>       const size_t chunk_size = 1 * 1024 * 1024;
>       g_autofree void *transfer_buf = NULL;
> @@ -2291,6 +2292,7 @@ fail:
>   
>   int vhost_load_backend_state(struct vhost_dev *dev, QEMUFile *f, Error **errp)
>   {
> +    ERRP_GUARD();
>       size_t transfer_buf_size = 0;
>       g_autofree void *transfer_buf = NULL;
>       g_autoptr(GError) g_err = NULL;

Reviewed-by: Thomas Huth <thuth@redhat.com>