Re: [PATCH] netdev: Use flexible array for trailing private bytes

From: Alexander Lobakin <aleksander.lobakin@intel.com>
To: Jakub Kicinski <kuba@kernel.org>
Cc: Eric Dumazet <edumazet@google.com>,
	Kees Cook <keescook@chromium.org>,
	"David S. Miller" <davem@davemloft.net>,
	Paolo Abeni <pabeni@redhat.com>,
	Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	"Gustavo A. R. Silva" <gustavoars@kernel.org>,
	<netdev@vger.kernel.org>, <linux-hardening@vger.kernel.org>,
	Simon Horman <horms@kernel.org>, "Jiri Pirko" <jiri@resnulli.us>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Coco Li <lixiaoyan@google.com>,
	Amritha Nambiar <amritha.nambiar@intel.com>,
	<linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] netdev: Use flexible array for trailing private bytes
Date: Mon, 4 Mar 2024 15:32:51 +0100	[thread overview]
Message-ID: <ae6b1114-1c71-46f0-82e5-23b9f05df1bf@intel.com> (raw)
In-Reply-To: <20240301093517.428e5b5d@kernel.org>

From: Jakub Kicinski <kuba@kernel.org>
Date: Fri, 1 Mar 2024 09:35:17 -0800

> On Fri, 1 Mar 2024 15:30:03 +0100 Alexander Lobakin wrote:
>> I like the idea of declaring priv explicitly rather than doing size +
>> ptr magic. But maybe we could just add this flex array to struct
>> net_device and avoid introducing a new structure.
> 
> 100% I should have linked to the thread that led to Kees's work.
> Adding directly to net_device would be way better but there's
> a handful of drivers which embed the struct.

I think it's okay to embed a struct with flex array at the end as long
as it's not used? Or the compiler will say that the flex array is not at
the end of the structure?

> If we can switch them to dynamic allocation, that'd be great.

It's mega weird to embed &net_device rather than do alloc_*dev() >_<

> And, as you may be alluding to, it removes the need for the WARN_ON()
> entirely as well.

Thanks,
Olek