[02/17] hw/net/xen_nic: Fix missing ERRP_GUARD() for error_prepend()

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 the pointer of
error_fatal, the user can't see this additional information, because
exit() happens in error_setg earlier than information is added [1].

The xen_netdev_connect() passes @errp to error_prepend(), and its @errp
parameter is from xen_device_frontend_changed().

Though its @errp points to @local_err of xen_device_frontend_changed(),
to follow the requirement of @errp, add missing ERRP_GUARD() at the
beginning of this function.

[1]: Issue description in the commit message of commit ae7c80a7bd73
     ("error: New macro ERRP_GUARD()").

Cc: Stefano Stabellini <sstabellini@kernel.org>
Cc: Anthony Perard <anthony.perard@citrix.com>
Cc: Paul Durrant <paul@xen.org>
Cc: Jason Wang <jasowang@redhat.com>
Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
---
 hw/net/xen_nic.c | 1 +
 1 file changed, 1 insertion(+)

On 29/02/2024 15.38, 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 the pointer of
> error_fatal, the user can't see this additional information, because
> exit() happens in error_setg earlier than information is added [1].
> 
> The xen_netdev_connect() passes @errp to error_prepend(), and its @errp
> parameter is from xen_device_frontend_changed().
> 
> Though its @errp points to @local_err of xen_device_frontend_changed(),
> to follow the requirement of @errp, add missing ERRP_GUARD() at the
> beginning of this function.
> 
> [1]: Issue description in the commit message of commit ae7c80a7bd73
>       ("error: New macro ERRP_GUARD()").
> 
> Cc: Stefano Stabellini <sstabellini@kernel.org>
> Cc: Anthony Perard <anthony.perard@citrix.com>
> Cc: Paul Durrant <paul@xen.org>
> Cc: Jason Wang <jasowang@redhat.com>
> Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
> ---
>   hw/net/xen_nic.c | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/hw/net/xen_nic.c b/hw/net/xen_nic.c
> index 453fdb981983..89487b49baf9 100644
> --- a/hw/net/xen_nic.c
> +++ b/hw/net/xen_nic.c
> @@ -351,6 +351,7 @@ static bool net_event(void *_xendev)
>   
>   static bool xen_netdev_connect(XenDevice *xendev, Error **errp)
>   {
> +    ERRP_GUARD();
>       XenNetDev *netdev = XEN_NET_DEVICE(xendev);
>       unsigned int port, rx_copy;
>   

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

On Thu, Feb 29, 2024 at 06:25:40PM +0100, Thomas Huth wrote:
> On 29/02/2024 15.38, 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 the pointer of
> > error_fatal, the user can't see this additional information, because
> > exit() happens in error_setg earlier than information is added [1].
> > 
> > The xen_netdev_connect() passes @errp to error_prepend(), and its @errp
> > parameter is from xen_device_frontend_changed().
> > 
> > Though its @errp points to @local_err of xen_device_frontend_changed(),
> > to follow the requirement of @errp, add missing ERRP_GUARD() at the
> > beginning of this function.
> > 
> > [1]: Issue description in the commit message of commit ae7c80a7bd73
> >       ("error: New macro ERRP_GUARD()").
> > 
> > Cc: Stefano Stabellini <sstabellini@kernel.org>
> > Cc: Anthony Perard <anthony.perard@citrix.com>
> > Cc: Paul Durrant <paul@xen.org>
> > Cc: Jason Wang <jasowang@redhat.com>
> > Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
> > ---
> >   hw/net/xen_nic.c | 1 +
> >   1 file changed, 1 insertion(+)
> > 
> > diff --git a/hw/net/xen_nic.c b/hw/net/xen_nic.c
> > index 453fdb981983..89487b49baf9 100644
> > --- a/hw/net/xen_nic.c
> > +++ b/hw/net/xen_nic.c
> > @@ -351,6 +351,7 @@ static bool net_event(void *_xendev)
> >   static bool xen_netdev_connect(XenDevice *xendev, Error **errp)
> >   {
> > +    ERRP_GUARD();
> >       XenNetDev *netdev = XEN_NET_DEVICE(xendev);
> >       unsigned int port, rx_copy;
> 
> Reviewed-by: Thomas Huth <thuth@redhat.com>

Acked-by: Anthony PERARD <anthony.perard@citrix.com>

Thanks,