netdev - Re: [PATCH net 1/3] net_sched: sch_sfq: use a temporary work area for validating configuration

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Message-ID: <Z+nYlgveEBukySzX@pop-os.localdomain>
Date: Sun, 30 Mar 2025 16:49:42 -0700
From: Cong Wang <xiyou.wangcong@...il.com>
To: Octavian Purdila <tavip@...gle.com>
Cc: jhs@...atatu.com, jiri@...nulli.us, davem@...emloft.net,
	edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
	horms@...nel.org, shuah@...nel.org, netdev@...r.kernel.org
Subject: Re: [PATCH net 1/3] net_sched: sch_sfq: use a temporary work area
 for validating configuration

On Fri, Mar 28, 2025 at 01:16:32PM -0700, Octavian Purdila wrote:
> Many configuration parameters have influence on others (e.g. divisor
> -> flows -> limit, depth -> limit) and so it is difficult to correctly
> do all of the validation before applying the configuration. And if a
> validation error is detected late it is difficult to roll back a
> partially applied configuration.
> 
> To avoid these issues use a temporary work area to update and validate
> the configuration and only then apply the configuration to the
> internal state.
> 
> Signed-off-by: Octavian Purdila <tavip@...gle.com>
> ---
>  net/sched/sch_sfq.c | 60 ++++++++++++++++++++++++++++++++++++---------
>  1 file changed, 48 insertions(+), 12 deletions(-)
> 
> diff --git a/net/sched/sch_sfq.c b/net/sched/sch_sfq.c
> index 65d5b59da583..027a3fde2139 100644
> --- a/net/sched/sch_sfq.c
> +++ b/net/sched/sch_sfq.c
> @@ -631,6 +631,18 @@ static int sfq_change(struct Qdisc *sch, struct nlattr *opt,
>  	struct red_parms *p = NULL;
>  	struct sk_buff *to_free = NULL;
>  	struct sk_buff *tail = NULL;
> +	/* work area for validating changes before committing them */
> +	struct {
> +		int limit;
> +		unsigned int divisor;
> +		unsigned int maxflows;
> +		int perturb_period;
> +		unsigned int quantum;
> +		u8 headdrop;
> +		u8 maxdepth;
> +		u8 flags;
> +	} tmp;

Thanks for your patch. It reminds me again about the lacking of complete
RCU support in TC. ;-)

Instead of using a temporary struct, how about introducing a new one
called struct sfq_sched_opt and putting it inside struct sfq_sched_data?
It looks more elegant to me.

Regards,
Cong