diff --git a/Makefile b/Makefile
index a1d8775adb..0da98b9274 100644
--- a/Makefile
+++ b/Makefile
@@ -772,6 +772,7 @@ LIB_OBJS += branch.o
 LIB_OBJS += bulk-checkin.o
 LIB_OBJS += bundle.o
 LIB_OBJS += cache-tree.o
+LIB_OBJS += chdir-notify.o
 LIB_OBJS += checkout.o
 LIB_OBJS += color.o
 LIB_OBJS += column.o
diff --git a/chdir-notify.c b/chdir-notify.c
new file mode 100644
index 0000000000..5f7f2c2ac2
--- /dev/null
+++ b/chdir-notify.c
@@ -0,0 +1,93 @@
+#include "cache.h"
+#include "chdir-notify.h"
+#include "list.h"
+#include "strbuf.h"
+
+struct chdir_notify_entry {
+	const char *name;
+	chdir_notify_callback cb;
+	void *data;
+	struct list_head list;
+};
+static LIST_HEAD(chdir_notify_entries);
+
+void chdir_notify_register(const char *name,
+			   chdir_notify_callback cb,
+			   void *data)
+{
+	struct chdir_notify_entry *e = xmalloc(sizeof(*e));
+	e->name = name;
+	e->cb = cb;
+	e->data = data;
+	list_add_tail(&e->list, &chdir_notify_entries);
+}
+
+static void reparent_cb(const char *name,
+			const char *old_cwd,
+			const char *new_cwd,
+			void *data)
+{
+	char **path = data;
+	char *tmp = *path;
+
+	if (!tmp)
+		return;
+
+	*path = reparent_relative_path(old_cwd, new_cwd, tmp);
+	free(tmp);
+
+	if (name) {
+		trace_printf_key(&trace_setup_key,
+				 "setup: reparent %s to '%s'",
+				 name, *path);
+	}
+}
+
+void chdir_notify_reparent(const char *name, char **path)
+{
+	chdir_notify_register(name, reparent_cb, path);
+}
+
+int chdir_notify(const char *new_cwd)
+{
+	struct strbuf old_cwd = STRBUF_INIT;
+	struct list_head *pos;
+
+	if (strbuf_getcwd(&old_cwd) < 0)
+		return -1;
+	if (chdir(new_cwd) < 0) {
+		int saved_errno = errno;
+		strbuf_release(&old_cwd);
+		errno = saved_errno;
+		return -1;
+	}
+
+	trace_printf_key(&trace_setup_key,
+			 "setup: chdir from '%s' to '%s'",
+			 old_cwd.buf, new_cwd);
+
+	list_for_each(pos, &chdir_notify_entries) {
+		struct chdir_notify_entry *e =
+			list_entry(pos, struct chdir_notify_entry, list);
+		e->cb(e->name, old_cwd.buf, new_cwd, e->data);
+	}
+
+	strbuf_release(&old_cwd);
+	return 0;
+}
+
+char *reparent_relative_path(const char *old_cwd,
+			     const char *new_cwd,
+			     const char *path)
+{
+	char *ret, *full;
+
+	if (is_absolute_path(path))
+		return xstrdup(path);
+
+	full = xstrfmt("%s/%s", old_cwd, path);
+	ret = xstrdup(remove_leading_path(full, new_cwd));
+	free(full);
+
+	return ret;
+}
diff --git a/chdir-notify.h b/chdir-notify.h
new file mode 100644
index 0000000000..366e4c1ee9
--- /dev/null
+++ b/chdir-notify.h
@@ -0,0 +1,73 @@
+#ifndef CHDIR_NOTIFY_H
+#define CHDIR_NOTIFY_H
+
+/*
+ * An API to let code "subscribe" to changes to the current working directory.
+ * The general idea is that some code asks to be notified when the working
+ * directory changes, and other code that calls chdir uses a special wrapper
+ * that notifies everyone.
+ */
+
+/*
+ * Callers who need to know about changes can do:
+ *
+ *   void foo(const char *old_path, const char *new_path, void *data)
+ *   {
+ *	warning("switched from %s to %s!", old_path, new_path);
+ *   }
+ *   ...
+ *   chdir_notify_register("description", foo, data);
+ *
+ * In practice most callers will want to move a relative path to the new root;
+ * they can use the reparent_relative_path() helper for that. If that's all
+ * you're doing, you can also use the convenience function:
+ *
+ *   chdir_notify_reparent("description", &my_path);
+ *
+ * Whenever a chdir event occurs, that will update my_path (if it's relative)
+ * to adjust for the new cwd by freeing any existing string and allocating a
+ * new one.
+ *
+ * Registered functions are called in the order in which they were added. Note
+ * that there's currently no way to remove a function, so make sure that the
+ * data parameter remains valid for the rest of the program.
+ *
+ * The "name" argument is used only for printing trace output from
+ * $GIT_TRACE_SETUP. It may be NULL, but if non-NULL should point to
+ * storage which lasts as long as the registration is active.
+ */
+typedef void (*chdir_notify_callback)(const char *name,
+				      const char *old_cwd,
+				      const char *new_cwd,
+				      void *data);
+void chdir_notify_register(const char *name, chdir_notify_callback cb, void *data);
+void chdir_notify_reparent(const char *name, char **path);
+
+/*
+ *
+ * Callers that want to chdir:
+ *
+ *   chdir_notify(new_path);
+ *
+ * to switch to the new path and notify any callbacks.
+ *
+ * Note that you don't need to chdir_notify() if you're just temporarily moving
+ * to a directory and back, as long as you don't call any subscribed code in
+ * between (but it should be safe to do so if you're unsure).
+ */
+int chdir_notify(const char *new_cwd);
+
+/*
+ * Reparent a relative path from old_root to new_root. For example:
+ *
+ *   reparent_relative_path("/a", "/a/b", "b/rel");
+ *
+ * would return the (newly allocated) string "rel". Note that we may return an
+ * absolute path in some cases (e.g., if the resulting path is not inside
+ * new_cwd).
+ */
+char *reparent_relative_path(const char *old_cwd,
+			     const char *new_cwd,
+			     const char *path);
+
+#endif /* CHDIR_NOTIFY_H */