netdev - Re: [PATCH net-next 1/2] net_tstamp: add new flag HWTSTAMP_FLAGS_UNSTABLE

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Date:   Wed, 8 Dec 2021 07:20:22 -0800
From:   Richard Cochran <richardcochran@...il.com>
To:     Hangbin Liu <liuhangbin@...il.com>
Cc:     netdev@...r.kernel.org, Jay Vosburgh <j.vosburgh@...il.com>,
        Veaceslav Falico <vfalico@...il.com>,
        Andy Gospodarek <andy@...yhouse.net>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Heiner Kallweit <hkallweit1@...il.com>
Subject: Re: [PATCH net-next 1/2] net_tstamp: add new flag
 HWTSTAMP_FLAGS_UNSTABLE_PHC


> diff --git a/include/uapi/linux/net_tstamp.h b/include/uapi/linux/net_tstamp.h
> index fcc61c73a666..d3aaab8396ef 100644
> --- a/include/uapi/linux/net_tstamp.h
> +++ b/include/uapi/linux/net_tstamp.h
> @@ -62,7 +62,7 @@ struct so_timestamping {
>  /**
>   * struct hwtstamp_config - %SIOCGHWTSTAMP and %SIOCSHWTSTAMP parameter
>   *
> - * @flags:	no flags defined right now, must be zero for %SIOCSHWTSTAMP
> + * @flags:	one of HWTSTAMP_FLAGS_*

Nit: should be FLAG (singular) not FLAGS.
1 bit set -> 1 flag enabled

>   * @tx_type:	one of HWTSTAMP_TX_*
>   * @rx_filter:	one of HWTSTAMP_FILTER_*
>   *
> @@ -78,6 +78,19 @@ struct hwtstamp_config {
>  	int rx_filter;
>  };
>  
> +/* possible values for hwtstamp_config->flags */
> +enum hwtstamp_flags {
> +	/*
> +	 * With this flag the user should aware that the PHC index
> +	 * get/set by syscall is not stable. e.g. the phc index of
> +	 * bond active interface may changed after failover.
> +	 */
> +	HWTSTAMP_FLAGS_UNSTABLE_PHC = (1<<0),

Can we please find a different name?  I see this, and I think,
"unstable ptp hw clock".  Nobody would want to use such a clock.

How about HWTSTAMP_FLAG_BONDED_PHC_INDEX ?

> +	/* add new constants above here */
> +	__HWTSTAMP_FLAGS_CNT
> +};

I guess that the original intent of hwtstamp_config.flags was for user
space to SET flags that it wanted.  Now this has become a place for
drivers to return values back.  Please make the input/output
distinction clear in the comments.

Thanks,
Richard