Re: [PATCH net-next v1 01/10] xfrm: extend add policy callback to set failure reason

[Paolo Abeni <pabeni@redhat.com>]

On Thu, 2023-01-26 at 09:28 +0200, Leon Romanovsky wrote:
> On Wed, Jan 25, 2023 at 11:02:26AM -0800, Jakub Kicinski wrote:
> > On Tue, 24 Jan 2023 13:54:57 +0200 Leon Romanovsky wrote:
> > > -	err = dev->xfrmdev_ops->xdo_dev_policy_add(xp);
> > > +	err = dev->xfrmdev_ops->xdo_dev_policy_add(xp, extack);
> > >  	if (err) {
> > >  		xdo->dev = NULL;
> > >  		xdo->real_dev = NULL;
> > >  		xdo->type = XFRM_DEV_OFFLOAD_UNSPECIFIED;
> > >  		xdo->dir = 0;
> > >  		netdev_put(dev, &xdo->dev_tracker);
> > > -		NL_SET_ERR_MSG(extack, "Device failed to offload this policy");
> > 
> > In a handful of places we do:
> > 
> > if (!extack->msg)
> > 	NL_SET_ERR_MSG(extack, "Device failed to offload this policy");
> > 
> > in case the device did not provide the extack.
> > Dunno if it's worth doing here.
> 
> Honestly, I followed devlink.c which didn't do that, but looked again
> and found that devlink can potentially overwrite messages :)
> 
> For example in this case:
>     997         err = ops->port_fn_state_get(port, &state, &opstate, extack);
>     998         if (err) {
>     999                 if (err == -EOPNOTSUPP)
>    1000                         return 0;
>    1001                 return err;
>    1002         }
>    1003         if (!devlink_port_fn_state_valid(state)) {
>    1004                 WARN_ON_ONCE(1);
>    1005                 NL_SET_ERR_MSG_MOD(extack, "Invalid state read from driver");
>    1006                 return -EINVAL;
>    1007         }
> 
> 
> So what do you think about the following change, so we can leave
> NL_SET_ERR_MSG_MOD() in devlink and xfrm intact? 
> 
> diff --git a/include/linux/netlink.h b/include/linux/netlink.h
> index 38f6334f408c..d6f3a958e30b 100644
> --- a/include/linux/netlink.h
> +++ b/include/linux/netlink.h
> @@ -101,7 +101,7 @@ struct netlink_ext_ack {
>                                                         \
>         do_trace_netlink_extack(__msg);                 \
>                                                         \
> -       if (__extack)                                   \
> +       if (__extack && !__extack->msg)                 \
>                 __extack->_msg = __msg;                 \
>  } while (0)
> 
> @@ -111,7 +111,7 @@ struct netlink_ext_ack {
>  #define NL_SET_ERR_MSG_FMT(extack, fmt, args...) do {                         \
>         struct netlink_ext_ack *__extack = (extack);                           \
>                                                                                \
> -       if (!__extack)                                                         \
> +       if (!__extack || __extack->msg)                                        \
>                 break;                                                         \
>         if (snprintf(__extack->_msg_buf, NETLINK_MAX_FMTMSG_LEN,               \
>                      "%s" fmt "%s", "", ##args, "") >=                         \
> 

I think it makes sense. With the above patch 3/10 should be updated to
preserve the 'catch-all' error message, I guess.

Let's see what Jakub thinks ;)

Cheers,

Paolo