Enhancements to zpool dry run mode.

In dry run mode, zpool should display more of the proposed pool
configuration for "zpool add".  This commit adds support for displaying
cache devices.

Signed-off-by: Tim Chase <tim@chase2k.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue openzfs#1106

cmd/zpool/zpool_main.c

@@ -593,6 +593,10 @@ zpool_do_add(int argc, char **argv)
 
 	if (dryrun) {
 		nvlist_t *poolnvroot;
+		nvlist_t **l2child;
+		uint_t l2children, c;
+		char *vname;
+		boolean_t hadcache = B_FALSE;
 
 		verify(nvlist_lookup_nvlist(config, ZPOOL_CONFIG_VDEV_TREE,
 		    &poolnvroot) == 0);
@@ -612,6 +616,30 @@ zpool_do_add(int argc, char **argv)
 			print_vdev_tree(zhp, "logs", nvroot, 0, B_TRUE);
 		}
 
+		/* Do the same for the caches */
+		if (nvlist_lookup_nvlist_array(poolnvroot, ZPOOL_CONFIG_L2CACHE,
+		    &l2child, &l2children) == 0 && l2children) {
+			hadcache = B_TRUE;
+			(void) printf(gettext("\tcache\n"));
+			for (c = 0; c < l2children; c++) {
+				vname = zpool_vdev_name(g_zfs, NULL,
+				    l2child[c], B_FALSE);
+				(void) printf("\t  %s\n", vname);
+				free(vname);
+			}
+		}
+		if (nvlist_lookup_nvlist_array(nvroot, ZPOOL_CONFIG_L2CACHE,
+		    &l2child, &l2children) == 0 && l2children) {
+			if (!hadcache)
+				(void) printf(gettext("\tcache\n"));
+			for (c = 0; c < l2children; c++) {
+				vname = zpool_vdev_name(g_zfs, NULL,
+				    l2child[c], B_FALSE);
+				(void) printf("\t  %s\n", vname);
+				free(vname);
+			}
+		}
+
 		ret = 0;
 	} else {
 		ret = (zpool_add(zhp, nvroot) != 0);