Re: [PATCH net-next 02/15] net: dsa: sja1105: Remove usage of iterator for list_add() after loop

[Vladimir Oltean]

Hello Jakob,

On Thu, Apr 07, 2022 at 12:28:47PM +0200, Jakob Koschel wrote:
> In preparation to limit the scope of a list iterator to the list
> traversal loop, use a dedicated pointer to point to the found element [1].
> 
> Before, the code implicitly used the head when no element was found
> when using &pos->list. Since the new variable is only set if an
> element was found, the list_add() is performed within the loop
> and only done after the loop if it is done on the list head directly.
> 
> Link: https://lore.kernel.org/all/CAHk-=wgRr_D8CB-D9Kg-c=EHreAsk5SqXPwr9Y7k9sA6cWXJ6w@xxxxxxxxxxxxxx/ [1]
> Signed-off-by: Jakob Koschel <jakobkoschel@xxxxxxxxx>
> ---
>  drivers/net/dsa/sja1105/sja1105_vl.c | 14 +++++++++-----
>  1 file changed, 9 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/net/dsa/sja1105/sja1105_vl.c b/drivers/net/dsa/sja1105/sja1105_vl.c
> index b7e95d60a6e4..cfcae4d19eef 100644
> --- a/drivers/net/dsa/sja1105/sja1105_vl.c
> +++ b/drivers/net/dsa/sja1105/sja1105_vl.c
> @@ -27,20 +27,24 @@ static int sja1105_insert_gate_entry(struct sja1105_gating_config *gating_cfg,
>  	if (list_empty(&gating_cfg->entries)) {
>  		list_add(&e->list, &gating_cfg->entries);
>  	} else {
> -		struct sja1105_gate_entry *p;
> +		struct sja1105_gate_entry *p = NULL, *iter;
>  
> -		list_for_each_entry(p, &gating_cfg->entries, list) {
> -			if (p->interval == e->interval) {
> +		list_for_each_entry(iter, &gating_cfg->entries, list) {
> +			if (iter->interval == e->interval) {
>  				NL_SET_ERR_MSG_MOD(extack,
>  						   "Gate conflict");
>  				rc = -EBUSY;
>  				goto err;
>  			}
>  
> -			if (e->interval < p->interval)
> +			if (e->interval < iter->interval) {
> +				p = iter;
> +				list_add(&e->list, iter->list.prev);
>  				break;
> +			}
>  		}
> -		list_add(&e->list, p->list.prev);
> +		if (!p)
> +			list_add(&e->list, gating_cfg->entries.prev);
>  	}
>  
>  	gating_cfg->num_entries++;
> -- 
> 2.25.1
> 

I apologize in advance if I've misinterpreted the end goal of your patch.
I do have a vague suspicion I understand what you're trying to achieve,
and in that case, would you mind using this patch instead of yours?
I think it still preserves the intention of the code in a clean manner.

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