linux-kernel - Re: [PATCHv3 next] ptp/ioctl: support MONOTONIC_RAW timestamps for PTP_SYS_OFFSET

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Date: Fri, 26 Apr 2024 11:21:10 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Mahesh Bandewar <maheshb@...gle.com>, Netdev <netdev@...r.kernel.org>, 
 Linux <linux-kernel@...r.kernel.org>, David Miller <davem@...emloft.net>,
 Jakub Kicinski <kuba@...nel.org>, Eric Dumazet <edumazet@...gle.com>,
 Thomas Gleixner <tglx@...utronix.de>, Richard Cochran
 <richardcochran@...il.com>, Arnd Bergmann <arnd@...db.de>, Sagi Maimon
 <maimon.sagi@...il.com>
Cc: Jonathan Corbet <corbet@....net>, John Stultz <jstultz@...gle.com>, 
	Mahesh Bandewar <mahesh@...dewar.net>
Subject: Re: [PATCHv3 next] ptp/ioctl: support MONOTONIC_RAW timestamps for
 PTP_SYS_OFFSET_EXTENDED

On Mon, 2024-04-22 at 15:07 -0700, Mahesh Bandewar wrote:
> diff --git a/include/uapi/linux/ptp_clock.h b/include/uapi/linux/ptp_clock.h
> index 053b40d642de..02684d7e00e6 100644
> --- a/include/uapi/linux/ptp_clock.h
> +++ b/include/uapi/linux/ptp_clock.h
> @@ -155,13 +155,27 @@ struct ptp_sys_offset {
>  	struct ptp_clock_time ts[2 * PTP_MAX_SAMPLES + 1];
>  };
>  
> +/*
> + * ptp_sys_offset_extended - data structure for IOCTL operation
> + *			     PTP_SYS_OFFSET_EXTENDED
> + *
> + * @n_samples:	Desired number of measurements.
> + * @clockid:	clockid of a clock-base used for pre/post timestamps.
> + * @rsv:	Reserved for future use.
> + * @ts:		Array of samples in the form [pre-TS, PHC, post-TS]. The
> + *		kernel provides @n_samples.
> + *
> + * History:
> + * v1: Initial implementation.
> + *
> + * v2: Use the first word of the reserved-field for @clockid. That's
> + *     backword compatible since v1 expects @rsv[3] to be 0 while the

Minor nit ^^^ 'backward'

> + *     clockid for CLOCK_REALTIME is '0'.
> + */
>  struct ptp_sys_offset_extended {
> -	unsigned int n_samples; /* Desired number of measurements. */
> -	unsigned int rsv[3];    /* Reserved for future use. */
> -	/*
> -	 * Array of [system, phc, system] time stamps. The kernel will provide
> -	 * 3*n_samples time stamps.
> -	 */
> +	unsigned int n_samples;
> +	__kernel_clockid_t clockid;
> +	unsigned int rsv[2];

AFAICS, here you are using the 'old' rsv[0] as 'clockid'

Please either always use rsv[0] instead of rsv[2] or re-order the
fields.

Thanks,

Paolo