Add "prof.dump_prefix" to override filename prefixes for dumps.

test/unit/prof_idump.c

@@ -1,5 +1,7 @@
 #include "test/jemalloc_test.h"
 
+#define TEST_PREFIX "test_prefix"
+
 static bool did_prof_dump_open;
 
 static int
@@ -8,6 +10,10 @@ prof_dump_open_intercept(bool propagate_err, const char *filename) {
 
 	did_prof_dump_open = true;
 
+	const char filename_prefix[] = TEST_PREFIX ".";
+	assert_d_eq(strncmp(filename_prefix, filename, sizeof(filename_prefix)
+	    - 1), 0, "Dump file name should start with \"" TEST_PREFIX ".\"");
+
 	fd = open("/dev/null", O_WRONLY);
 	assert_d_ne(fd, -1, "Unexpected open() failure");
 
@@ -18,9 +24,16 @@ TEST_BEGIN(test_idump) {
 	bool active;
 	void *p;
 
+	const char *dump_prefix = TEST_PREFIX;
+
 	test_skip_if(!config_prof);
 
 	active = true;
+
+	assert_d_eq(mallctl("prof.dump_prefix", NULL, NULL,
+	    (void *)&dump_prefix, sizeof(dump_prefix)), 0,
+	    "Unexpected mallctl failure while overwriting dump prefix");
+
 	assert_d_eq(mallctl("prof.active", NULL, NULL, (void *)&active,
 	    sizeof(active)), 0,
 	    "Unexpected mallctl failure while activating profiling");