free(host->hcps.prlist_val);
host->hcps.prlist_val = NULL;
host->hcps.prlist_len = 0;
+ free(host->tmay_caps.Capabilities_val);
+ host->tmay_caps.Capabilities_val = NULL;
+ host->tmay_caps.Capabilities_len = 0;
DeleteAllCallBacks_r(host, 1);
host->hostFlags &= ~RESETDONE; /* just to be safe */
return 0;
}
+/*
+ * The following few functions deal with caching TellMeAboutYourself calls
+ * that we issued to clients. Why do we do this? Well:
+ *
+ * Q: First, why do we need to issue a TMAY against a client on an incoming new
+ * Rx connection?
+ *
+ * A: We must verify that the incoming Rx connection is the same host that
+ * we have a 'host' structure for. On new calls for existing connections, we
+ * can remember which host corresponds to that connection, but for new
+ * connections, we have no way to find what host it is for, except by looking
+ * up the host by IP address. Since hosts can change IP addresses, we need to
+ * contact the IP address to see if it's the host we think it is.
+ *
+ * Q: Okay, then why cache the results?
+ *
+ * A: The TMAY calls to a single host are serialized, because they are issued
+ * with the host's host->lock held. If we get 4 Rx calls each on new
+ * connections to the same host at the same time, the 1st call will lock the
+ * host, and issue a TMAY. Once that's done, the second call will issue a
+ * TMAY, then the 3rd and then the 4th. However, the 3rd and 4th calls have
+ * been waiting to issue a TMAY since before the 2nd call even _started_ to
+ * issue a TMAY. So, we can just effectively give the results of the 2nd
+ * call's TMAY to the 3rd and 4th, too. Since it is nondeterministic which of
+ * those calls gets to issue a TMAY "first", we can just assume they all got
+ * the same result.
+ *
+ * Note that in the above example, we cannot reuse the results of the 1st TMAY
+ * for the 2nd, 3rd, and 4th calls (we only reuse the results of the 2nd).
+ * This is because by the time the 2nd call starts waiting for the host lock,
+ * it doesn't know how long the 1st TMAY has been running, so the 2nd call
+ * might indeed get a different TMAY result (though this probably would be
+ * extremely rare).
+ *
+ * Anyway, so, if we don't cache the results, we are issuing TMAYs that are
+ * pure overhead. In an environment with clients that create a lot of
+ * connections to a fileserver (keep in mind each new PAG on OpenAFS clients
+ * creates a new connection), this can mean a significant amount of overhead.
+ * So, we use this "TMAY cache" to avoid this overhead for the common case.
+ */
+/**
+ * Should we skip calling TellMeAboutYourself on this host, and instead rely
+ * on cached TMAY results?
+ *
+ * @param[in] host The host we are dealing with
+ * @param[in] prewait_tmays What the value of host->n_tmays was _before_ we
+ * locked 'host'
+ * @param[in] prewait_host What the primary IP address for 'host' was before
+ * we locked 'host'
+ * @param[in] prewait_port What the primary port was for 'host' before we
+ * locked 'host'
+ *
+ * @return Whether we should skip calling TMAY, and instead rely on cached
+ * results in host
+ */
+static int
+ShouldSkipTMAY(struct host *host, int prewait_tmays, afs_uint32 prewait_host,
+ afs_uint16 prewait_port)
+{
+ int skiptmay = 0;
+ if (host->n_tmays > prewait_tmays + 1) {
+ /* while we were waiting for the host lock, the in-progress TMAY
+ * call finished, someone else started a new TMAY call, and that
+ * finished. so, calling TMAY again won't give us any information
+ * or additional guarantees. */
+ skiptmay = 1;
+ }
+ if (host->host != prewait_host || host->port != prewait_port) {
+ /* ...but don't skip it if the host has changed */
+ skiptmay = 0;
+ }
+ return skiptmay;
+}
+
+/**
+ * If appropriate, simulate a TellMeAboutYourself call on 'host' by extracting
+ * cached interfaceAddr and Capabilities information from 'host' itself.
+ *
+ * @param[in] host The host we're dealing with
+ * @param[inout] askiptmay On entering this function, this should contain the
+ * result of ShouldSkipTMAY. On return, it is 1 if we
+ * actually did use cached TMAY results, or 0 if we
+ * did not.
+ * @param[out] interf The interfaceAddr result of the simulated TMAY call
+ * @param[out] caps The Capabilities result of the simulated TMAY call
+ *
+ * @return status
+ * @retval 0 We used the cached TMAY results; do NOT make a real TMAY request
+ * @retval otherwise We did not use cached TMAY results; issue a real TMAY request
+ */
+static int
+SimulateTMAY(struct host *host, int *askiptmay, struct interfaceAddr *interf,
+ Capabilities *caps)
+{
+ size_t capsize;
+
+ if (!*askiptmay) {
+ /* we're not supposed to skip the actual TMAY call */
+ return -1;
+ }
+
+ *interf = host->tmay_interf;
+
+ free(caps->Capabilities_val);
+ caps->Capabilities_val = NULL;
+ caps->Capabilities_len = 0;
+
+ if (!host->tmay_caps.Capabilities_val) {
+ return 0;
+ }
+
+ capsize = sizeof(caps->Capabilities_val[0]) * host->tmay_caps.Capabilities_len;
+
+ caps->Capabilities_val = malloc(capsize);
+ if (!caps->Capabilities_val) {
+ /* we should/did _not_ skip the real TMAY call, since we couldn't
+ * alloc memory to use the cached results */
+ *askiptmay = 0;
+ return -1;
+ }
+ caps->Capabilities_len = host->tmay_caps.Capabilities_len;
+ memcpy(caps->Capabilities_val, host->tmay_caps.Capabilities_val, capsize);
+
+ return 0;
+}
+
+/**
+ * If appropriate, store the given results from a real TellmeAboutYourself
+ * call, and cache them in the given host structure.
+ *
+ * @param[in] host The host we're dealing with
+ * @param[in] skiptmay 1 if we skipped making a real TMAY call, 0 otherwise
+ * @param[in] didtmay 1 if we issued a successful real TMAY call, 0 otherwise
+ * @param[in] interf The interfaceAddr result from the real TMAY call
+ * @param[in] caps The Capabilities result from the real TMAY call
+ */
+static void
+CacheTMAY(struct host *host, int skiptmay, int didtmay,
+ struct interfaceAddr *interf, Capabilities *caps)
+{
+ size_t capsize;
+
+ if (skiptmay) {
+ /* we simulated the TMAY call, so the state of the world hasn't
+ * changed; don't touch anything */
+ return;
+ }
+ if (!didtmay) {
+ /* we did not perform a successful TMAY, so we don't have valid
+ * results to cache. blow away the existing cache so we don't use
+ * stale results */
+ goto resetcache;
+ }
+ if (host->n_tmays == INT_MAX) {
+ /* make sure int rollover doesn't screw up our ordering */
+ goto resetcache;
+ }
+ if (host->lock.num_waiting == 0) {
+ /* nobody is waiting for this host, so no reason to cache anything */
+ goto resetcache;
+ }
+
+ /* okay, if we got here, everything looks good; let's cache the given
+ * 'interf' and 'caps' */
+
+ host->tmay_interf = *interf;
+
+ if (!caps->Capabilities_val) {
+ free(host->tmay_caps.Capabilities_val);
+ host->tmay_caps.Capabilities_val = NULL;
+ host->tmay_caps.Capabilities_len = 0;
+
+ } else {
+ if (caps->Capabilities_len != host->tmay_caps.Capabilities_len) {
+ free(host->tmay_caps.Capabilities_val);
+ host->tmay_caps.Capabilities_val = NULL;
+ host->tmay_caps.Capabilities_len = 0;
+ }
+
+ capsize = sizeof(caps->Capabilities_val[0]) * caps->Capabilities_len;
+
+ if (!host->tmay_caps.Capabilities_val) {
+ host->tmay_caps.Capabilities_val = malloc(capsize);
+ if (!host->tmay_caps.Capabilities_val) {
+ goto resetcache;
+ }
+ }
+
+ host->tmay_caps.Capabilities_len = caps->Capabilities_len;
+ memcpy(host->tmay_caps.Capabilities_val, caps->Capabilities_val, capsize);
+ }
+ host->n_tmays++;
+ return;
+
+ resetcache:
+ /* blow away the cached TMAY data; pretend we never saw anything */
+ free(host->tmay_caps.Capabilities_val);
+ host->tmay_caps.Capabilities_val = NULL;
+ host->tmay_caps.Capabilities_len = 0;
+ memset(&host->tmay_interf, 0, sizeof(host->tmay_interf));
+
+ host->n_tmays = 0;
+}
static int
h_threadquota(int waiting)
* structure for this address. Verify that the identity
* of the caller matches the identity in the host structure.
*/
+
+ int didtmay = 0; /* did we make a successful TMAY call against host->host? */
+ unsigned int prewait_tmays;
+ afs_uint32 prewait_host;
+ afs_uint16 prewait_port;
+ int skiptmay;
+
if ((host->hostFlags & HWHO_INPROGRESS) &&
h_threadquota(host->lock.num_waiting)) {
h_Release_r(host);
host = NULL;
goto gethost_out;
}
+
+ prewait_tmays = host->n_tmays;
+ prewait_host = host->host;
+ prewait_port = host->port;
+
h_Lock_r(host);
if (!(host->hostFlags & ALTADDR) ||
(host->hostFlags & HOSTDELETED)) {
cb_conn = host->callback_rxcon;
rx_GetConnection(cb_conn);
+
+ skiptmay = ShouldSkipTMAY(host, prewait_tmays, prewait_host, prewait_port);
+
H_UNLOCK;
if (haddr == host->host && hport == host->port) {
/* The existing callback connection matches the
* incoming connection so just use it.
*/
- code =
- RXAFSCB_TellMeAboutYourself(cb_conn, &interf, &caps);
- if (code == RXGEN_OPCODE)
- code = RXAFSCB_WhoAreYou(cb_conn, &interf);
+
+ if (SimulateTMAY(host, &skiptmay, &interf, &caps) == 0) {
+ /* noop; we don't need to call TellMeAboutYourself; we can
+ * trust the results from the last TMAY call */
+ code = 0;
+
+ } else {
+ code =
+ RXAFSCB_TellMeAboutYourself(cb_conn, &interf, &caps);
+ if (code == RXGEN_OPCODE)
+ code = RXAFSCB_WhoAreYou(cb_conn, &interf);
+ if (code == 0) {
+ didtmay = 1;
+ }
+ }
} else {
/* We do not have a match. Create a new connection
* for the new addr/port and use multi_Rx to probe
rx_PutConnection(cb_conn);
cb_conn=NULL;
H_LOCK;
+
+ CacheTMAY(host, skiptmay, didtmay, &interf, &caps);
+
if ((code == RXGEN_OPCODE) ||
((code == 0) && (afs_uuid_equal(&interf.uuid, &nulluuid)))) {
identP = malloc(sizeof(struct Identity));
git://git.openafs.org / openafs.git / blobdiff