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

Hello Jakub,

On 8. Apr 2022, at 05:54, Jakub Kicinski [off-list ref] wrote:

On Thu,  7 Apr 2022 12:28:47 +0200 Jakob Koschel wrote:

quoted

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);

This turns a pretty slick piece of code into something ugly :(
I'd rather you open coded the iteration here than make it more 
complex to satisfy "safe coding guidelines".

I'm not entirely sure I understand what you mean with 
"open coded the iteration". But maybe the solution proposed by Vladimir [1]
works for you? I'm planning to rewrite the cases in that way for the relevant
ones.

Also the list_add() could be converted to list_add_tail().

Good point, I wasn't sure if that's considered as something that should be
done as a separate change. I'm happy to include it in v2.

Thanks for the input.

	Jakob

[1] https://lore.kernel.org/linux-kernel/20220408114120.tvf2lxvhfqbnrlml@skbuf/ (local)