Re: [PATCH v1 net-next 02/14] net: Add a new socket option for a future transmit time.

From: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
To: Jesus Sanchez-Palencia <jesus.sanchez-palencia@intel.com>
Cc: "Network Development" <netdev@vger.kernel.org>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	jan.altenberg@linutronix.de,
	"Vinicius Gomes" <vinicius.gomes@intel.com>,
	kurt.kanzenbach@linutronix.de, "Henrik Austad" <henrik@austad.us>,
	"Richard Cochran" <richardcochran@gmail.com>,
	"Levi Pearson" <levi.pearson@harman.com>,
	ilias.apalodimas@linaro.org, ivan.khoronzhuk@linaro.org,
	"Miroslav Lichvar" <mlichvar@redhat.com>,
	"Willem de Bruijn" <willemb@google.com>,
	"Jamal Hadi Salim" <jhs@mojatatu.com>,
	"Cong Wang" <xiyou.wangcong@gmail.com>,
	"Jiří Pírko" <jiri@resnulli.us>,
	"Richard Cochran" <rcochran@linutronix.de>
Subject: Re: [PATCH v1 net-next 02/14] net: Add a new socket option for a future transmit time.
Date: Thu, 28 Jun 2018 10:40:23 -0400	[thread overview]
Message-ID: <CAF=yD-KccMgPRL67YY9X3U6jP9E1WVc3C=b=wnAZvW8URs1FMQ@mail.gmail.com> (raw)
In-Reply-To: <CAF=yD-KY60-Hi2_BSb2jOR7W91wOJQtSQ11WSDEDVpY6wx+aUw@mail.gmail.com>

On Thu, Jun 28, 2018 at 10:26 AM Willem de Bruijn
<willemdebruijn.kernel@gmail.com> wrote:
>
> On Wed, Jun 27, 2018 at 6:08 PM Jesus Sanchez-Palencia
> <jesus.sanchez-palencia@intel.com> wrote:
> >
> > From: Richard Cochran <rcochran@linutronix.de>
> >
> > This patch introduces SO_TXTIME. User space enables this option in
> > order to pass a desired future transmit time in a CMSG when calling
> > sendmsg(2). The argument to this socket option is a 6-bytes long struct
> > defined as:
> >
> > struct sock_txtime {
> >         clockid_t       clockid;
> >         u16             flags;
> > };
>
> clockid_t is __kernel_clockid_t is int is a variable length field.
> Please use fixed length fields.

Sorry, int is fine, of course, and clockid_t is used between userspace and
kernel already.

> Also, as MAX_CLOCKS is 16, only 4 bits are needed. A single u16
> is probably sufficient as cmsg argument. To future proof, a u32 will
> allow for more
> than 4 flags. But in struct sock, 16 bits should be sufficient to
> encode both clock id
> and flags.