Hey Christophe, > On 8. Apr 2022, at 09:47, Christophe Leroy <christophe.le...@csgroup.eu> > wrote: > > > > 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=ehreask5sqxpwr9y7k9sa6cwx...@mail.gmail.com/ >> [1] >> Signed-off-by: Jakob Koschel <jakobkosc...@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);
Thanks for the review and input. The code you are showing here would have an uninitialized access to 'p' if the list is empty. Also 'p->list.prev' will be the second last entry if the list iterator ran through completely, whereas the original code was pointing to the last entry of the list. IMO Vladimir Oltean posted a nice alternative way to solve it, see [1]. That way it keeps the semantics of the code the same and doesn't duplicate the list_add. > > > > Christophe [1] https://lore.kernel.org/linux-kernel/20220408114120.tvf2lxvhfqbnrlml@skbuf/ Thanks, Jakob
