python: fix iterators failing on empty lists

libnvme/nvme.i

@@ -395,6 +395,17 @@ PyObject *hostid_from_file();
 #include "fabrics.h"
 #define STR_OR_NONE(str) (!(str) ? "None" : str)
 
+struct nvme_host * nvme_first_host(struct nvme_root * r);
+struct nvme_host * nvme_next_host(struct nvme_root * r, struct nvme_host * h);
+struct nvme_subsystem * nvme_first_subsystem(struct nvme_host * h);
+struct nvme_subsystem * nvme_next_subsystem(struct nvme_host * h, struct nvme_subsystem * s);
+struct nvme_ctrl * nvme_subsystem_first_ctrl(struct nvme_subsystem * s);
+struct nvme_ctrl * nvme_subsystem_next_ctrl(struct nvme_subsystem * s, struct nvme_ctrl * c);
+struct nvme_ns * nvme_subsystem_first_ns(struct nvme_subsystem * s);
+struct nvme_ns * nvme_subsystem_next_ns(struct nvme_subsystem * s, struct nvme_ns * n);
+struct nvme_ns * nvme_ctrl_first_ns(struct nvme_ctrl * c);
+struct nvme_ns * nvme_ctrl_next_ns(struct nvme_ctrl * c, struct nvme_ns * n);
+
 struct nvme_root {
 	%immutable config_file;
 	%immutable application;
@@ -544,9 +555,14 @@ struct nvme_ns {
 		else if (!strcmp(level, "emerg")) log_level = LOG_EMERG;
 		nvme_init_logging($self, log_level, false, false);
 	}
-	struct nvme_host *hosts() {
-		return nvme_first_host($self);
-	}
+	%pythoncode %{
+	def hosts(self):
+	    """Iterator over all host objects"""
+	    h = nvme_first_host(self)
+	    while h:
+	        yield h
+	        h = nvme_next_host(self, h)
+	%}
 	void refresh_topology() {
 		nvme_refresh_topology($self);
 	}
@@ -620,9 +636,14 @@ struct nvme_ns {
 		};
 		return ret;
 	}
-	struct nvme_subsystem* subsystems() {
-		return nvme_first_subsystem($self);
-	}
+	%pythoncode %{
+	def subsystems(self):
+	    """Iterator over all subsystem objects"""
+	    s = nvme_first_subsystem(self)
+	    while s:
+	        yield s
+	        s = nvme_next_subsystem(self, s)
+	%}
 }
 
 %{
@@ -692,12 +713,22 @@ struct nvme_ns {
 		};
 		return ret;
 	}
-	struct nvme_ctrl *controllers() {
-		return nvme_subsystem_first_ctrl($self);
-	}
-	struct nvme_ns *namespaces() {
-		return nvme_subsystem_first_ns($self);
-	}
+	%pythoncode %{
+	def controllers(self):
+	    """Iterator over all controller objects"""
+	    c = nvme_subsystem_first_ctrl(self)
+	    while c:
+	        yield c
+	        c = nvme_subsystem_next_ctrl(self, c)
+	%}
+	%pythoncode %{
+	def namespaces(self):
+	    """Iterator over all namespace objects"""
+	    ns = nvme_subsystem_first_ns(self)
+	    while ns:
+	        yield ns
+	        ns = nvme_subsystem_next_ns(self, ns)
+	%}
 	%immutable name;
 	const char *name;
 	%immutable host;
@@ -898,9 +929,14 @@ struct nvme_ns {
 		};
 		return ret;
 	}
-	struct nvme_ns* namespaces() {
-		return nvme_ctrl_first_ns($self);
-	}
+	%pythoncode %{
+	def namespaces(self):
+	    """Iterator over all namespace objects"""
+	    ns = nvme_ctrl_first_ns(self)
+	    while ns:
+	        yield ns
+	        ns = nvme_ctrl_next_ns(self, ns)
+	%}
 }
 
 %{

libnvme/tests/gc.py

@@ -12,9 +12,6 @@
 host = nvme.host(root)
 print(f'host: {host}')
 
-subsystem = host.subsystems()
-print(f'subsystem: {subsystem}')
-
 ctrls = []
 for i in range(10):
     ctrl = nvme.ctrl(
@@ -25,8 +22,10 @@
     ctrls.append(ctrl)
     print(f'ctrl {i}: {ctrl}')
 
-ns = subsystem.namespaces() if subsystem is not None else None
-print(f'ns: {ns}')
+for s in host.subsystems():
+    print(f'subsystem: {s}')
+    for ns in s.namespaces():
+        print(f'ns: {ns}')
 
 # Deleting objects in the following order would create a segmentation
 # fault if it weren't for the %pythonappend in nvme.i. This test is to