nvmf: add spdk_nvmf_get_tgt function

This function will allow applications (and RPCs)
to obtain an spdk_nvmf_tgt pointer by name.

Change-Id: I82792e06a819e06d9fddb5429830008653d92cd1
Signed-off-by: Seth Howell <seth.howell@intel.com>
Reviewed-on: https://review.gerrithub.io/c/spdk/spdk/+/465349
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: Changpeng Liu <changpeng.liu@intel.com>
Reviewed-by: Broadcom SPDK FC-NVMe CI <spdk-ci.pdl@broadcom.com>
Reviewed-by: Jim Harris <james.r.harris@intel.com>

CHANGELOG.md

@@ -8,6 +8,11 @@ The `spdk_nvmf_tgt_create` function now accepts an object of type `spdk_nvmf_tar
 as its only parameter. This new structure contains the max_subsystems parameter previously
 passed into that function.
 
+A new public API function `spdk_nvmf_get_tgt` has been added which allows users to
+retrieve a pointer to an `spdk_nvmf_tgt` object by supplying its name. In the special
+case where an RPC or application only creates a single target, this function can accept
+a null name parameter and will return the only available target.
+
 ### nvme
 
 Added `no_shn_notification` to NVMe controller initialization options, users can enable

include/spdk/nvmf.h

@@ -136,6 +136,20 @@ void spdk_nvmf_tgt_destroy(struct spdk_nvmf_tgt *tgt,
 			   spdk_nvmf_tgt_destroy_done_fn cb_fn,
 			   void *cb_arg);
 
+/**
+ * Get a pointer to an NVMe-oF target.
+ *
+ * In order to support some legacy applications and RPC methods that may rely on the
+ * concept that there is only one target, the name parameter can be passed as NULL.
+ * If there is only one available target, that target will be returned.
+ * Otherwise, name is a required parameter.
+ *
+ * \param name The name provided when the target was created.
+ *
+ * \return The target with the given name, or NULL if no match was found.
+ */
+struct spdk_nvmf_tgt *spdk_nvmf_get_tgt(const char *name);
+
 /**
  * Write NVMe-oF target configuration into provided JSON context.
  * \param w JSON write context

lib/nvmf/nvmf.c

@@ -320,6 +320,34 @@ spdk_nvmf_tgt_destroy(struct spdk_nvmf_tgt *tgt,
 	spdk_io_device_unregister(tgt, spdk_nvmf_tgt_destroy_cb);
 }
 
+struct spdk_nvmf_tgt *
+spdk_nvmf_get_tgt(const char *name)
+{
+	struct spdk_nvmf_tgt *tgt;
+	uint32_t num_targets = 0;
+
+	TAILQ_FOREACH(tgt, &g_nvmf_tgts, link) {
+		if (name) {
+			if (!strncmp(tgt->name, name, strlen(tgt->name))) {
+				return tgt;
+			}
+		}
+		num_targets++;
+	}
+
+	/*
+	 * special case. If there is only one target and
+	 * no name was specified, return the only available
+	 * target. If there is more than one target, name must
+	 * be specified.
+	 */
+	if (!name && num_targets == 1) {
+		return TAILQ_FIRST(&g_nvmf_tgts);
+	}
+
+	return NULL;
+}
+
 static void
 spdk_nvmf_write_subsystem_config_json(struct spdk_json_write_ctx *w,
 				      struct spdk_nvmf_subsystem *subsystem)