FreeBSD boot code reminder only if bootfs set

As suggested in openzfs#12099 (and after sleeping over it), change
zpool upgrade so that a reminder to update the boot code
is only shown if the zpool in question has the bootfs
property set. This should be sufficient for the vast
majority of installations. People rolling something
else/custom are most likely aware what to do in their
setup anyway.

Signed-off-by: Michael Gmelin <grembo@FreeBSD.org>

cmd/zpool/zpool_main.c

@@ -8889,10 +8889,15 @@ upgrade_cb(zpool_handle_t *zhp, void *arg)
 
 	if (modified_pool) {
 #ifdef __FreeBSD__
-		(void) printf(gettext("\nIf you boot from pool '%s', "
-		    "please also update the boot code.\nSee gptzfsboot(8) "
-		    "and loader.efi(8) for details.\n"),
-		    zpool_get_name(zhp));
+		char bootfs[ZPOOL_MAXPROPLEN];
+		if (zpool_get_prop(zhp, ZPOOL_PROP_BOOTFS, bootfs,
+		    sizeof (bootfs), NULL, B_FALSE) == 0 &&
+		    strcmp(bootfs, "-") != 0) {
+			(void) printf(gettext("\nPool '%s' has the bootfs "
+			    "property set, you might need to update\nthe boot "
+			    "code. See gptzfsboot(8) and loader.efi(8) for "
+			    "details.\n"), zpool_get_name(zhp));
+		}
 #else
 		(void) printf("\n");
 #endif
@@ -9059,10 +9064,15 @@ upgrade_one(zpool_handle_t *zhp, void *data)
 
 	if (modified_pool) {
 #ifdef __FreeBSD__
-		(void) printf(gettext("\nIf you boot from pool '%s', "
-		    "please also update the boot code.\nSee gptzfsboot(8) "
-		    "and loader.efi(8) for details.\n"),
-		    zpool_get_name(zhp));
+		char bootfs[ZPOOL_MAXPROPLEN];
+		if (zpool_get_prop(zhp, ZPOOL_PROP_BOOTFS, bootfs,
+		    sizeof (bootfs), NULL, B_FALSE) == 0 &&
+		    strcmp(bootfs, "-") != 0) {
+			(void) printf(gettext("\nPool '%s' has the bootfs "
+			    "property set, you might need to update\nthe boot "
+			    "code. See gptzfsboot(8) and loader.efi(8) for "
+			    "details.\n"), zpool_get_name(zhp));
+		}
 #else
 		(void) printf("\n");
 #endif