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

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Date:   Thu, 28 Jun 2018 10:40:23 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Jesus Sanchez-Palencia <jesus.sanchez-palencia@...el.com>
Cc:     Network Development <netdev@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        jan.altenberg@...utronix.de,
        Vinicius Gomes <vinicius.gomes@...el.com>,
        kurt.kanzenbach@...utronix.de, Henrik Austad <henrik@...tad.us>,
        Richard Cochran <richardcochran@...il.com>,
        Levi Pearson <levi.pearson@...man.com>,
        ilias.apalodimas@...aro.org, ivan.khoronzhuk@...aro.org,
        Miroslav Lichvar <mlichvar@...hat.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiří Pírko <jiri@...nulli.us>,
        Richard Cochran <rcochran@...utronix.de>
Subject: Re: [PATCH v1 net-next 02/14] net: Add a new socket option for a
 future transmit time.

On Thu, Jun 28, 2018 at 10:26 AM Willem de Bruijn
<willemdebruijn.kernel@...il.com> wrote:
>
> On Wed, Jun 27, 2018 at 6:08 PM Jesus Sanchez-Palencia
> <jesus.sanchez-palencia@...el.com> wrote:
> >
> > From: Richard Cochran <rcochran@...utronix.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.