qa: nested_note checks that notes are enqueued in kernel

qa/kern/nested_note.c

@@ -0,0 +1,48 @@
+#include <u.h>
+#include <lib9.h>
+
+int done;
+int waited;
+
+void
+handler(void *v, char *s)
+{
+	int i;
+	if(strcmp(s, "stop") == 0){
+		done = 1;
+		noted(NCONT);
+	}
+	print("waiting after %s", s);
+	for(i = 0; i < 1000*1000; ++i)
+		if(i % 4999 == 0)
+			print(".");
+	print("\n");
+	print("wait after %s terminated\n", s);
+	waited++;
+	noted(NCONT);
+}
+
+void
+main(int argc, char**argv)
+{
+	int fd;
+	if(argc > 1){
+		fd = ocreate(argv[1], OWRITE, 0666);
+		dup(fd, 1);
+		close(fd);
+	}
+
+	if (notify(handler)){
+		fprint(2, "%r\n");
+		exits("notify fails");
+	}
+
+	print("note handler installed\n");
+
+	while(!done)
+		sleep(100);
+	if(waited == 2){
+		print("PASS\n");
+		exits(0);
+	}
+}