netdev - Re: [PATCH net-next v3 1/4] net_tstamp: add SCM_TS_OPT_ID to provide OPT

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Message-ID: <CAL+tcoATsEEqsNPqoL0aPZDkeb-6KPmrzokiB2PiOEmE9kjfhw@mail.gmail.com>
Date: Thu, 5 Sep 2024 16:49:03 +0800
From: Jason Xing <kerneljasonxing@...il.com>
To: Vadim Fedorenko <vadim.fedorenko@...ux.dev>
Cc: Vadim Fedorenko <vadfed@...a.com>, Willem de Bruijn <willemb@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, David Ahern <dsahern@...nel.org>, 
	Simon Horman <horms@...nel.org>, netdev@...r.kernel.org
Subject: Re: [PATCH net-next v3 1/4] net_tstamp: add SCM_TS_OPT_ID to provide
 OPT_ID in control message

On Thu, Sep 5, 2024 at 4:34 PM Vadim Fedorenko
<vadim.fedorenko@...ux.dev> wrote:
>
> On 05/09/2024 09:24, Jason Xing wrote:
> > Hello Vadim,
> >
> > On Wed, Sep 4, 2024 at 7:32 PM Vadim Fedorenko <vadfed@...a.com> wrote:
> > [...]
> >> diff --git a/include/uapi/linux/net_tstamp.h b/include/uapi/linux/net_tstamp.h
> >> index a2c66b3d7f0f..1c38536350e7 100644
> >> --- a/include/uapi/linux/net_tstamp.h
> >> +++ b/include/uapi/linux/net_tstamp.h
> >> @@ -38,6 +38,13 @@ enum {
> >>                                   SOF_TIMESTAMPING_LAST
> >>   };
> >>
> >> +/*
> >> + * The highest bit of sk_tsflags is reserved for kernel-internal
> >> + * SOCKCM_FLAG_TS_OPT_ID. This check is to control that SOF_TIMESTAMPING*
> >> + * values do not reach this reserved area
> >
> > I wonder if we can add the above description which is quite useful in
> > enum{} like this:
> >
> > diff --git a/include/uapi/linux/net_tstamp.h b/include/uapi/linux/net_tstamp.h
> > index a2c66b3d7f0f..2314fccaf51d 100644
> > --- a/include/uapi/linux/net_tstamp.h
> > +++ b/include/uapi/linux/net_tstamp.h
> > @@ -13,7 +13,12 @@
> >   #include <linux/types.h>
> >   #include <linux/socket.h>   /* for SO_TIMESTAMPING */
> >
> > -/* SO_TIMESTAMPING flags */
> > +/* SO_TIMESTAMPING flags
> > + *
> > + * The highest bit of sk_tsflags is reserved for kernel-internal
> > + * SOCKCM_FLAG_TS_OPT_ID.
> > + * SOCKCM_FLAG_TS_OPT_ID = (1 << 31),
> > + */
> >   enum {
> >          SOF_TIMESTAMPING_TX_HARDWARE = (1<<0),
> >          SOF_TIMESTAMPING_TX_SOFTWARE = (1<<1),
> >
> > to explicitly remind the developers not to touch 1<<31 field. Or else,
> > it can be very hard to trace who occupied the highest field in the
> > future at the first glance, I think.
> >
> > [...]
>
> That's a bit contradictory to Willem's comment about not exposing
> implementation details to UAPI headers, which I think makes sense.

Oh, well, I missed checking the filename... it's an uapi file, sorry
for the noise :(

>
> I will move the comment to the definition area of SOCKCM_FLAG_TS_OPT_ID
> and will try to add meaningful message to BUILD_BUG_ON() to make it
> easier for developers to understand the problem.

Great! Thanks!