mctpd: add bridged endpoint polling mechanism

Implement endpoint periodic polling mechanism to validate bridged
endpoint accessiblity. Begin polling as soon as gateway routes are
created. Stop polling once it's established that endpoint path is
accessible.

Publish peer path once downstream endpoint responds to send poll
command.

Signed-off-by: Faizan Ali <faizana@nvidia.com>

Author: faizana-nvidia

src/mctpd.c

@@ -101,6 +101,12 @@ struct role {
 	const char *dbus_val;
 };
 
+// Endpoint poll context for bridged endpoint polling
+struct poll_ctx {
+	struct peer *bridge;
+	mctp_eid_t poll_eid;
+};
+
 static const struct role roles[] = {
 	[ENDPOINT_ROLE_UNKNOWN] = {
 		.role = ENDPOINT_ROLE_UNKNOWN,
@@ -199,6 +205,10 @@ struct peer {
 	// Pool size
 	uint8_t pool_size;
 	uint8_t pool_start;
+
+	struct {
+		sd_event_source **sources;
+	} poll;
 };
 
 struct ctx {
@@ -4756,6 +4766,139 @@ static int endpoint_send_allocate_endpoint_ids(
 	return rc;
 }
 
+static int peer_endpoint_poll(sd_event_source *s, uint64_t usec, void *userdata)
+{
+	struct poll_ctx *pctx = userdata;
+	struct peer *bridge = pctx->bridge;
+	struct net *n;
+	struct peer *peer = NULL;
+	mctp_eid_t ep = pctx->poll_eid;
+	mctp_eid_t pool_start = bridge->pool_start;
+	mctp_eid_t ret_eid = 0;
+	int rc = 0, idx = ep - pool_start;
+
+	/* Polling policy :
+	 *
+	 * Once bridge eid pool space is allocated and gateway
+	 * routes for downstream endpoints are in place, busowner
+	 * would initiate periodic GET_ENDPOINT_ID command at an
+	 * interval of atleast 1/2 * TRECLAIM.
+
+	 1. The downstream endpoint if present behind the bridge,
+	    responds to send poll command, that endpoint path is
+		considered accessible.
+		The endpoint path would be published as reachable to d-bus and
+		polling will no longer continue.
+
+	 2. If endpoint is not present or doesn't responds to send poll
+	    commmand, then it has not been establed yet that endpoint
+		path from the bridge is accessible or not, thus continue
+		to poll.	
+	 */
+
+	if (!bridge) {
+		warnx("Bridge (eid %d) removed?", bridge->eid);
+		goto exit;
+	}
+
+	n = lookup_net(bridge->ctx, bridge->net);
+	peer = n->peers[ep];
+	if (!peer) {
+		rc = add_peer(bridge->ctx, &(bridge->phys), ep, bridge->net,
+			      &peer, true);
+		if (rc < 0)
+			goto exit;
+	}
+
+	rc = query_endpoint_poll_commmand(peer, &ret_eid);
+	if (rc < 0) {
+		goto reschedule;
+	}
+
+	if (ret_eid != ep) {
+		warnx("Unexpected eid %d abort polling for eid %d", ret_eid,
+		      ep);
+		goto exit;
+	}
+
+	if (bridge->ctx->verbose) {
+		fprintf(stderr, "Endpoint %d is accessible\n", ep);
+	}
+
+	rc = setup_added_peer(peer);
+	if (rc < 0)
+		goto reschedule;
+
+	goto exit;
+
+reschedule:
+	if (!bridge) {
+		warnx("Bridge (eid %d) removed?", bridge->eid);
+		goto exit;
+	}
+
+	rc = sd_event_source_set_time_relative(bridge->poll.sources[idx],
+					       bridge->ctx->endpoint_poll);
+	if (rc >= 0) {
+		rc = sd_event_source_set_enabled(bridge->poll.sources[idx],
+						 SD_EVENT_ONESHOT);
+	}
+	return 0;
+
+exit:
+	if (bridge) {
+		assert(sd_event_source_get_enabled(bridge->poll.sources[idx],
+						   NULL) == 0);
+		sd_event_source_unref(bridge->poll.sources[idx]);
+		bridge->poll.sources[idx] = NULL;
+	}
+	free(pctx);
+	return rc < 0 ? rc : 0;
+}
+
+static int bridge_poll_start(struct peer *bridge)
+{
+	struct ctx *ctx;
+	int rc;
+	mctp_eid_t pool_start = bridge->pool_start;
+	mctp_eid_t pool_size = bridge->pool_size;
+	int i;
+	ctx = bridge->ctx;
+	sd_event_source **sources =
+		calloc(pool_size, sizeof(sd_event_source *));
+
+	if (!sources) {
+		rc = -ENOMEM;
+		warnx("Failed to setup periodic polling for bridge (eid %d)",
+		      bridge->eid);
+		return rc;
+	}
+
+	bridge->poll.sources = sources;
+	for (i = 0; i < pool_size; i++) {
+		struct poll_ctx *pctx = calloc(1, sizeof(struct poll_ctx));
+		if (!pctx) {
+			warnx("Failed to memory, skip polling for eid %d",
+			      pool_start + i);
+			continue;
+		}
+
+		pctx->bridge = bridge;
+		pctx->poll_eid = pool_start + i;
+		rc = sd_event_add_time_relative(
+			ctx->event, &bridge->poll.sources[i], CLOCK_MONOTONIC,
+			ctx->endpoint_poll, 0, peer_endpoint_poll, pctx);
+		if (rc < 0) {
+			warnx("Failed to setup poll event source for eid %d",
+			      (pool_start + i));
+			free(pctx);
+			continue;
+		}
+	}
+
+	return 0;
+}
+
 static int endpoint_allocate_eids(struct peer *peer)
 {
 	uint8_t allocated_pool_size = 0;
@@ -4814,7 +4957,8 @@ static int endpoint_allocate_eids(struct peer *peer)
 			peer->pool_size);
 	}
 
-	// TODO: Polling logic for downstream EID
+	// Poll for downstream endpoint accessibility
+	bridge_poll_start(peer);
 
 	return 0;
 }