Linux Ethernet Bridging - Jan 2023 - [Bridge] [PATCH net-next] netlink: provide an ability to set default extack message

On Thu, Jan 26, 2023 at 02:37:23PM -0800, Jakub Kicinski
wrote:
> On Fri, 27 Jan 2023 00:32:13 +0200 Vladimir Oltean wrote:
> > On Thu, Jan 26, 2023 at 09:15:03PM +0200, Leon Romanovsky wrote:
> > > From: Leon Romanovsky <leonro at nvidia.com>
> > > 
> > > In netdev common pattern, xxtack pointer is forwarded to the
drivers
> >                             ~~~~~~
> >                             extack
> > 
> > > to be filled with error message. However, the caller can easily
> > > overwrite the filled message.
> > > 
> > > Instead of adding multiple "if (!extack->_msg)"
checks before any
> > > NL_SET_ERR_MSG() call, which appears after call to the driver,
let's
> > > add this check to common code.
> > > 
> > > [1] https://lore.kernel.org/all/Y9Irgrgf3uxOjwUm at unreal
> > > Signed-off-by: Leon Romanovsky <leonro at nvidia.com>
> > > ---  
> > 
> > I would somewhat prefer not doing this, and instead introducing a new
> > NL_SET_ERR_MSG_WEAK() of sorts.
> 
> That'd be my preference too, FWIW. It's only the offload cases
which
> need this sort of fallback.
Of course not, almost any error unwind path which sets extack will need it.
See devlink as an example, but I'm confident that same issue exists in other
places too.

You are suggesting API which is very easy to do wrong.

So I prefer to stay with my proposal if it is possible.

Thanks

On Fri, 27 Jan 2023 07:26:13 +0200 Leon Romanovsky
wrote:
> > That'd be my preference too, FWIW. It's only the offload cases
which
> > need this sort of fallback.  
> 
> Of course not, almost any error unwind path which sets extack will need it.
I guess we can come up with scenarios where the new behavior would 
be useful. But the fact is - your patch changes 4 places...
> See devlink as an example
I don't know what part of devlink you mean at a quick scroll.