libnvme: Add nvme_getifaddrs()

The POSIX `getifaddrs()` API returns the list of network
interfaces on the system, but invoking it can be costly. On
large-scale systems with hundreds of NVMe-over-TCP connections,
this API may be called hundreds of times, resulting in increased
latency.

This patch introduces `nvme_getifaddrs()`, a wrapper around
`getifaddrs()` that caches the results on the first invocation
and reuses the cached data on subsequent calls.

Signed-off-by: Martin Belanger <[email protected]>

Author: Martin Belanger

libnvme/src/nvme/tree.c

@@ -531,6 +531,8 @@ void nvme_free_global_ctx(struct nvme_global_ctx *ctx)
 	free(ctx->config_file);
 	free(ctx->application);
 	free(ctx);
+
+	nvme_getifaddrs(NULL); /* Free cached I/F addresses */
 }
 
 void nvme_root_release_fds(struct nvme_global_ctx *ctx)
@@ -1787,9 +1789,9 @@ static ctrl_match_t _candidate_init(struct candidate_args *candidate,
 
 	if (streq0(transport, "tcp")) {
 		/* For TCP we may need to access the interface map.
-		 * Let's retrieve and cache the map.
+		 * Let's retrieve the (cached) map.
 		 */
-		if (getifaddrs(&candidate->iface_list) == -1)
+		if (nvme_getifaddrs(&candidate->iface_list) == -1)
 			candidate->iface_list = NULL;
 
 		candidate->addreq = nvme_ipaddrs_eq;
@@ -1813,7 +1815,10 @@ static ctrl_match_t _candidate_init(struct candidate_args *candidate,
  */
 static void _candidate_free(struct candidate_args *candidate)
 {
-	freeifaddrs(candidate->iface_list); /* This is NULL-safe */
+	/* iface_list points to cached data owned by nvme_getifaddrs().
+	 * Do not free here. The memory will be released when we free the
+	 * global context.
+	 */
 }
 
 #define _cleanup_candidate_ __cleanup__(_candidate_free)

libnvme/src/nvme/util.c

@@ -1142,6 +1142,31 @@ bool nvme_iface_primary_addr_matches(const struct ifaddrs *iface_list, const cha
 
 #endif /* HAVE_NETDB */
 
+int nvme_getifaddrs(struct ifaddrs **ifap)
+{
+	static struct ifaddrs *ifaddrs_cache;
+	static bool ifaddrs_cached;
+
+	if (!ifap) {
+		freeifaddrs(ifaddrs_cache); /* NULL-safe */
+		ifaddrs_cache = NULL;
+		ifaddrs_cached = false;
+		return 0;
+	}
+
+	if (!ifaddrs_cached) {
+		if (getifaddrs(&ifaddrs_cache) == -1) {
+			ifaddrs_cache = NULL;
+			*ifap = NULL;
+			return -1;
+		}
+		ifaddrs_cached = true;
+	}
+
+	*ifap = ifaddrs_cache;
+	return 0;
+}
+
 void *__nvme_alloc(size_t len)
 {
 	size_t _len = round_up(len, 0x1000);

libnvme/src/nvme/util.h

@@ -758,6 +758,21 @@ int nvme_uuid_find(struct nvme_id_uuid_list *uuid_list, const unsigned char uuid
  */
 bool nvme_ipaddrs_eq(const char *addr1, const char *addr2);
 
+/**
+ * nvme_getifaddrs - Cached wrapper around getifaddrs()
+ * @ifap: Output pointer to the cached interface address list. If
+ *      NULL, then free the cache.
+ *
+ * On the first call, this function invokes the POSIX getifaddrs()
+ * and caches the result. Subsequent calls return the cached data.
+ * The caller must NOT call freeifaddrs() on the returned data.
+ * Use nvme_getifaddrs() with ifap set to NULL to release the
+ * cache when done.
+ *
+ * Return: 0 on success, -1 on error (with errno set).
+ */
+int nvme_getifaddrs(struct ifaddrs **ifap);
+
 /**
  * nvme_iface_matching_addr - Get interface matching @addr
  * @iface_list: Interface list returned by getifaddrs()