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sysctl_search_oid: remove useless tests

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sysctl_search_old makes several tests in a loop that can be removed.

The first test in the loop is only ever true on the first loop
iteration, and is always true on that iteration, so its work can be
done before the loop begins.

The upper and lower bounds on the loop variable 'indx' are each tested
on each iteration, but 'indx' is changed in one direction or the other
only once within the loop, so only one bound needs to be checked.

Two ways remain in the loop that nodes[indx] can change (after one of
them is put before the loop start), and one of them applies exactly
when indx has been incremented, so no separate test for that case
requires testing.

Restructure and add comments that makes clearer that this is a basic
depth-first search.

Reviewed by:	hselasky
Differential Revision:	https://reviews.freebsd.org/D36741
This commit is contained in:
Doug Moore 2022-09-27 13:30:31 -05:00
parent f092c21bf6
commit e96ae5cb05
1 changed files with 22 additions and 17 deletions
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39
sys/kern/kern_sysctl.c
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@ -356,29 +356,34 @@ sysctl_search_oid(struct sysctl_oid **nodes, struct sysctl_oid *needle)
SYSCTL_ASSERT_LOCKED();
indx = 0;
while (indx < CTL_MAXNAME && indx >= 0) {
if (nodes[indx] == NULL && indx == 0)
nodes[indx] = RB_MIN(sysctl_oid_list,
&sysctl__children);
else if (nodes[indx] == NULL)
nodes[indx] = RB_MIN(sysctl_oid_list,
&nodes[indx - 1]->oid_children);
else
nodes[indx] = RB_NEXT(sysctl_oid_list,
&nodes[indx - 1]->oid_children, nodes[indx]);
/*
* Do a depth-first search of the oid tree, looking for 'needle'. Start
* with the first child of the root.
*/
nodes[indx] = RB_MIN(sysctl_oid_list, &sysctl__children);
for (;;) {
if (nodes[indx] == needle)
return (indx + 1);
if (nodes[indx] == NULL) {
indx--;
continue;
}
if ((nodes[indx]->oid_kind & CTLTYPE) == CTLTYPE_NODE) {
indx++;
/* Node has no more siblings, so back up to parent. */
if (indx-- == 0) {
/* Retreat to root, so give up. */
break;
}
} else if ((nodes[indx]->oid_kind & CTLTYPE) == CTLTYPE_NODE) {
/* Node has children. */
if (++indx == CTL_MAXNAME) {
/* Max search depth reached, so give up. */
break;
}
/* Start with the first child. */
nodes[indx] = RB_MIN(sysctl_oid_list,
&nodes[indx - 1]->oid_children);
continue;
}
/* Consider next sibling. */
nodes[indx] = RB_NEXT(sysctl_oid_list, NULL, nodes[indx]);
}
return (-1);
}