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Add tests for hash function, and comment dns_rbt_addnode() (#41179)

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This commit is contained in:
Mukund Sivaraman
2016-02-08 14:51:53 +05:30
parent 0c29904b27
commit 614ce1b65f
3 changed files with 154 additions and 16 deletions
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55
lib/dns/rbt.c
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@@ -1128,6 +1128,37 @@ dns_rbt_addnode(dns_rbt_t *rbt, dns_name_t *name, dns_rbtnode_t **nodep) {
REQUIRE(dns_name_isabsolute(name));
REQUIRE(nodep != NULL && *nodep == NULL);
/*
* Dear future BIND developer,
*
* After you have tried attempting to optimize this routine by
* using the hashtable and have realized your folly, please
* append another cross ("X") below as a warning to the next
* future BIND developer:
*
* Number of victim developers: X
*
* I wish the past developer had included such a notice.
*
* Long form: Unlike dns_rbt_findnode(), this function does not
* lend itself to be optimized using the hashtable:
*
* 1. In the subtree where the insertion occurs, this function
* needs to have the insertion point and the order where the
* lookup terminated (i.e., at the insertion point where left or
* right child is NULL). This cannot be determined from the
* hashtable, so at least in that subtree, a BST O(log N) lookup
* is necessary.
*
* 2. Our RBT nodes contain not only single labels but label
* sequences to optimize space usage. So at every level, we have
* to look for a match in the hashtable for all superdomains in
* the rest of the name we're searching. This is an O(N)
* operation at least, here N being the label size of name, each
* of which is a hashtable lookup involving dns_name_equal()
* comparisons.
*/
/*
* Create a copy of the name so the original name structure is
* not modified.
@@ -1437,7 +1468,7 @@ dns_rbt_findnode(dns_rbt_t *rbt, dns_name_t *name, dns_name_t *foundname,
unsigned int options, dns_rbtfindcallback_t callback,
void *callback_arg)
{
dns_rbtnode_t *current, *last_compared, *current_root;
dns_rbtnode_t *current, *last_compared;
dns_rbtnodechain_t localchain;
dns_name_t *search_name, current_name, *callback_name;
dns_fixedname_t fixedcallbackname, fixedsearchname;
@@ -1494,7 +1525,6 @@ dns_rbt_findnode(dns_rbt_t *rbt, dns_name_t *name, dns_name_t *foundname,
saved_result = ISC_R_SUCCESS;
current = rbt->root;
current_root = rbt->root;
while (ISC_LIKELY(current != NULL)) {
NODENAME(current, &current_name);
@@ -1531,22 +1561,23 @@ dns_rbt_findnode(dns_rbt_t *rbt, dns_name_t *name, dns_name_t *foundname,
unsigned int hash;
/*
* The case of current != current_root, that
* means a left or right pointer was followed,
* only happens when the algorithm fell through to
* the traditional binary search because of a
* bitstring label. Since we dropped the bitstring
* support, this should not happen.
* The case of current not being a subtree root,
* that means a left or right pointer was
* followed, only happens when the algorithm
* fell through to the traditional binary search
* because of a bitstring label. Since we
* dropped the bitstring support, this should
* not happen.
*/
INSIST(current == current_root);
INSIST(IS_ROOT(current));
nlabels = dns_name_countlabels(search_name);
/*
* current_root is the root of the current level, so
* current is the root of the current level, so
* its parent is the same as its "up" pointer.
*/
up_current = PARENT(current_root);
up_current = PARENT(current);
dns_name_init(&hash_name, NULL);
hashagain:
@@ -1714,8 +1745,6 @@ dns_rbt_findnode(dns_rbt_t *rbt, dns_name_t *name, dns_name_t *foundname,
* Finally, head to the next tree level.
*/
current = DOWN(current);
current_root = current;
} else {
/*
* Though there are labels in common, the