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/private.h

@@ -13,6 +13,8 @@
 #include <poll.h>
 #include <sys/socket.h>
 #include <sys/stat.h>
+#include <sys/types.h>
+#include <ifaddrs.h>
 
 #include <nvme/fabrics.h>
 #include <nvme/mi.h>
@@ -273,6 +275,7 @@ struct nvme_global_ctx {
 	bool create_only;
 	bool dry_run;
 	struct nvme_fabric_options *options;
+	struct ifaddrs *ifaddrs_cache; /* init with nvme_getifaddrs() */
 };
 
 struct nvmf_discovery_ctx {
@@ -552,4 +555,18 @@ static inline char *xstrdup(const char *s)
 	return strdup(s);
 }
 
+/**
+ * nvme_getifaddrs - Cached wrapper around getifaddrs()
+ * @ctx: pointer to the global context
+ *
+ * On the first call, this function invokes the POSIX getifaddrs()
+ * and caches the result in the global context. Subsequent calls
+ * return the cached data. The caller must NOT call freeifaddrs()
+ * on the returned data. The cache will be freed when the global
+ * context is freed.
+ *
+ * Return: Pointer to I/F data, NULL on error (with errno set).
+ */
+const struct ifaddrs *nvme_getifaddrs(struct nvme_global_ctx *ctx);
+
 #endif /* _LIBNVME_PRIVATE_H */

libnvme/src/nvme/tree.c

@@ -55,7 +55,7 @@ struct candidate_args {
 	const char *subsysnqn;
 	const char *host_traddr;
 	const char *host_iface;
-	struct ifaddrs *iface_list;
+	const struct ifaddrs *iface_list;
 	bool (*addreq)(const char *, const char *);
 	bool well_known_nqn;
 };
@@ -525,6 +525,9 @@ void nvme_free_global_ctx(struct nvme_global_ctx *ctx)
 	if (!ctx)
 		return;
 
+	freeifaddrs(ctx->ifaddrs_cache); /* NULL-safe */
+	ctx->ifaddrs_cache = NULL;
+
 	free(ctx->options);
 	nvme_for_each_host_safe(ctx, h, _h)
 		__nvme_free_host(h);
@@ -1756,7 +1759,8 @@ static bool _match_ctrl(struct nvme_ctrl *c, struct candidate_args *candidate)
  * Return: The matching function to use when comparing an existing
  * controller to the candidate controller.
  */
-static ctrl_match_t _candidate_init(struct candidate_args *candidate,
+static ctrl_match_t _candidate_init(struct nvme_global_ctx *ctx,
+				    struct candidate_args *candidate,
 				    const char *transport,
 				    const char *traddr,
 				    const char *trsvcid,
@@ -1786,12 +1790,7 @@ 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.
-		 */
-		if (getifaddrs(&candidate->iface_list) == -1)
-			candidate->iface_list = NULL;
-
+		candidate->iface_list = nvme_getifaddrs(ctx); /* TCP only */
 		candidate->addreq = nvme_ipaddrs_eq;
 		return _tcp_match_ctrl;
 	}
@@ -1806,30 +1805,19 @@ static ctrl_match_t _candidate_init(struct candidate_args *candidate,
 	return _match_ctrl;
 }
 
-/**
- * _candidate_free() - Release resources allocated by _candidate_init()
- *
- * @candidate:	data to free.
- */
-static void _candidate_free(struct candidate_args *candidate)
-{
-	freeifaddrs(candidate->iface_list); /* This is NULL-safe */
-}
-
-#define _cleanup_candidate_ __cleanup__(_candidate_free)
-
 nvme_ctrl_t __nvme_lookup_ctrl(nvme_subsystem_t s, const char *transport,
 			       const char *traddr, const char *host_traddr,
 			       const char *host_iface, const char *trsvcid,
 			       const char *subsysnqn, nvme_ctrl_t p)
 {
-	_cleanup_candidate_ struct candidate_args candidate = {};
+	struct candidate_args candidate = {};
 	struct nvme_ctrl *c, *matching_c = NULL;
 	ctrl_match_t ctrl_match;
 
 	/* Init candidate and get the matching function to use */
-	ctrl_match = _candidate_init(&candidate, transport, traddr, trsvcid,
-				     subsysnqn, host_traddr, host_iface);
+	ctrl_match = _candidate_init(s->h->ctx, &candidate, transport, traddr,
+				     trsvcid, subsysnqn, host_traddr,
+				     host_iface);
 
 	c = p ? nvme_subsystem_next_ctrl(s, p) : nvme_subsystem_first_ctrl(s);
 	for (; c != NULL; c = nvme_subsystem_next_ctrl(s, c)) {
@@ -1847,12 +1835,13 @@ bool nvme_ctrl_config_match(struct nvme_ctrl *c, const char *transport,
 			    const char *subsysnqn, const char *host_traddr,
 			    const char *host_iface)
 {
-	_cleanup_candidate_ struct candidate_args candidate = {};
+	struct candidate_args candidate = {};
 	ctrl_match_t ctrl_match;
 
 	/* Init candidate and get the matching function to use */
-	ctrl_match = _candidate_init(&candidate, transport, traddr, trsvcid,
-				     subsysnqn, host_traddr, host_iface);
+	ctrl_match = _candidate_init(c->ctx, &candidate, transport, traddr,
+				     trsvcid, subsysnqn, host_traddr,
+				     host_iface);
 
 	return ctrl_match(c, &candidate);
 }

libnvme/src/nvme/util.c

@@ -1167,3 +1167,15 @@ void *__nvme_realloc(void *p, size_t len)
 
 	return result;
 }
+
+const struct ifaddrs *nvme_getifaddrs(struct nvme_global_ctx *ctx)
+{
+	if (!ctx->ifaddrs_cache) {
+		struct ifaddrs *p;
+
+		if (!getifaddrs(&p))
+			ctx->ifaddrs_cache = p;
+	}
+
+	return ctx->ifaddrs_cache;
+}