chdir-notify: add function to unregister listeners

While we (obviously) have a way to register new listeners that get
called whenever we chdir(3p), we don't have an equivalent that can be
used to unregister such a listener again.

Add one, as it will be required in a subsequent commit.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: pks-t

chdir-notify.c

@@ -25,6 +25,24 @@ void chdir_notify_register(const char *name,
 	list_add_tail(&e->list, &chdir_notify_entries);
 }
 
+void chdir_notify_unregister(const char *name, chdir_notify_callback cb,
+			     void *data)
+{
+	struct list_head *pos, *p;
+
+	list_for_each_safe(pos, p, &chdir_notify_entries) {
+		struct chdir_notify_entry *e =
+			list_entry(pos, struct chdir_notify_entry, list);
+
+		if (e->cb != cb || e->data != data || !e->name != !name ||
+		    (e->name && strcmp(e->name, name)))
+			continue;
+
+		list_del(pos);
+		free(e);
+	}
+}
+
 static void reparent_cb(const char *name,
 			const char *old_cwd,
 			const char *new_cwd,

chdir-notify.h

@@ -41,6 +41,8 @@ typedef void (*chdir_notify_callback)(const char *name,
 				      const char *new_cwd,
 				      void *data);
 void chdir_notify_register(const char *name, chdir_notify_callback cb, void *data);
+void chdir_notify_unregister(const char *name, chdir_notify_callback cb,
+			     void *data);
 void chdir_notify_reparent(const char *name, char **path);
 
 /*