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From:   Willem de Bruijn <willemdebruijn.kernel@gmail.com>
Date:   Fri, 31 Aug 2018 11:08:09 -0400
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Subject: Re: [PATCH net-next 1/3] net: rework SIOCGSTAMP ioctl handling
To:     Arnd Bergmann <arnd@arndb.de>
Cc:     Network Development <netdev@vger.kernel.org>,
        David Miller <davem@davemloft.net>, linux-arch@vger.kernel.org,
        y2038 Mailman List <y2038@lists.linaro.org>,
        Eric Dumazet <edumazet@google.com>,
        Willem de Bruijn <willemb@google.com>,
        LKML <linux-kernel@vger.kernel.org>, linux-hams@vger.kernel.org,
        linux-bluetooth@vger.kernel.org, linux-can@vger.kernel.org,
        dccp@vger.kernel.org, linux-wpan@vger.kernel.org,
        linux-sctp@vger.kernel.org, linux-x25@vger.kernel.org
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> > > Looking at it again, it seems that sock_gettstamp() should
> > > actually deal with this gracefully: it will return a -EINVAL
> > > error condition if the timestamp remains at the
> > > SK_DEFAULT_STAMP initial value, which is probably
> > > just as appropriate (or better) as the current -ENOTTY
> > > default, and if we are actually recording timestamps, we
> > > might just as well report them.
> >
> > Yes, that's a nice solution. There is always some risk in changing
> > error codes. But ioctl callers should be able to support newly
> > implemented functionality. Even if partially implemented and
> > returning ENOENT instead of ENOIOCTLCMD.
>
> Ok, so do you think we should stay with the current version
> for now, and change the two points later, or should I rework
> it to integrate the locking and removing the callback?
>
> I suppose the series actually gets nicer without the
> callback, since I can simply add the generic timestamping
> implementation first, and then remove the dead ioctl
> handlers.

Agreed. I would add the locks in a separate patch, if only on the
off-chance that lockdep discovers something and it will be easier
to bisect and revise independently. I can also follow up with that
patch outside this set, of course.