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

Christophe Leroy
2022-04-08T07:49:22Z

Le 07/04/2022 à 12:28, Jakob Koschel a écrit :
> 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@mail.gmail.com/ [1]
> Signed-off-by: Jakob Koschel <jakobkoschel@gmail.com>
> ---
> 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++;

This change looks ugly, why duplicating the list_add() to do the same ?
At the end of the loop the pointer contains gating_cfg->entries, so it
was cleaner before.

If you don't want to use the loop index outside the loop, fair enough,
all you have to do is:

struct sja1105_gate_entry *p, *iter;

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;
}
p = iter;

if (e->interval < iter->interval)
break;
}
list_add(&e->list, p->list.prev);

Christophe