netdev - Re: [PATCH net 1/2] ptp: check that rsv field is zero in struct ptp_sys_offset

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Message-ID: <20190108051923.2ozbytxqorxzpad5@localhost>
Date:   Mon, 7 Jan 2019 21:19:23 -0800
From:   Richard Cochran <richardcochran@...il.com>
To:     David Miller <davem@...emloft.net>
Cc:     esyr@...hat.com, mlichvar@...hat.com, netdev@...r.kernel.org,
        jacob.e.keller@...el.com, mtosatti@...hat.com
Subject: Re: [PATCH net 1/2] ptp: check that rsv field is zero in struct
 ptp_sys_offset_extended

On Mon, Jan 07, 2019 at 08:29:38AM -0800, David Miller wrote:
> From: Eugene Syromiatnikov <esyr@...hat.com>
> Date: Mon, 7 Jan 2019 16:22:29 +0100
> 
> > Otherwise it is impossible to use it for something else, as it will break
> > userspace that puts garbage there.
> > 
> > The same check should be done in other structures, but the fact that
> > data in reserved fields is ignored is already part of the kernel ABI.
> > 
> > Signed-off-by: Eugene Syromiatnikov <esyr@...hat.com>
> 
> I think the opportunity to enforce this has passed and you will break
> userspace by doing this.

Does this seriously mean that the 'rsv' field in

	struct ptp_extts_request {
		unsigned int index;  /* Which channel to configure. */
		unsigned int flags;  /* Bit field for PTP_xxx flags. */
		unsigned int rsv[2]; /* Reserved for future use. */
	};

can never be extended with some semantics?

Thanks,
Richard