sm-notify orphans an addrinfo struct in its address list rotation
logic if only a single result was returned from getaddrinfo(3).
For each host, the first time through notify_host(), we want to
send a PMAP_GETPORT request. ->ai is NULL, and retries is set to 100,
forcing a DNS lookup and an address rotation. If only a single
addrinfo struct is returned, the rotation logic causes a NULL to be
planted in ->ai, copied from the ai_next field of the returned result.
This means that the second time through notify_host() (to perform the
actual SM_NOTIFY call) we do a second DNS lookup, since ->ai is NULL.
The result of the first lookup has been orphaned, and extra network
traffic is generated.
This scenario is actually fairly common. Since we pass
.ai_protocol = IPPROTO_UDP,
to getaddrinfo(3), for most hosts, which have a single forward and
reverse pointer in the DNS database, we get back a single addrinfo
struct as a result.
To address this problem, only perform the address list rotation if
there is more than one element on the list returned by getaddrinfo(3).
Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
---
utils/statd/sm-notify.c | 34 +++++++++++++++++++++-------------
1 files changed, 21 insertions(+), 13 deletions(-)
diff --git a/utils/statd/sm-notify.c b/utils/statd/sm-notify.c
index f1fc619..78d0a59 100644
--- a/utils/statd/sm-notify.c
+++ b/utils/statd/sm-notify.c
@@ -424,19 +424,27 @@ notify_host(int sock, struct nsm_host *host)
* point.
*/
if (host->retries >= 4) {
- struct addrinfo *first = host->ai;
- struct addrinfo **next = &host->ai;
-
- /* remove the first entry from the list */
- host->ai = first->ai_next;
- first->ai_next = NULL;
- /* find the end of the list */
- next = &first->ai_next;
- while ( *next )
- next = & (*next)->ai_next;
- /* put first entry at end */
- *next = first;
- memcpy(&host->addr, first->ai_addr, first->ai_addrlen);
+ /* don't rotate if there is only one addrinfo */
+ if (host->ai->ai_next == NULL)
+ memcpy(&host->addr, host->ai->ai_addr,
+ host->ai->ai_addrlen);
+ else {
+ struct addrinfo *first = host->ai;
+ struct addrinfo **next = &host->ai;
+
+ /* remove the first entry from the list */
+ host->ai = first->ai_next;
+ first->ai_next = NULL;
+ /* find the end of the list */
+ next = &first->ai_next;
+ while ( *next )
+ next = & (*next)->ai_next;
+ /* put first entry at end */
+ *next = first;
+ memcpy(&host->addr, first->ai_addr,
+ first->ai_addrlen);
+ }
+
smn_set_port((struct sockaddr *)&host->addr, 0);
host->retries = 0;
}
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