path: root/chdir-notify.h
diff options
authorJeff King <>2018-03-30 18:35:04 (GMT)
committerJunio C Hamano <>2018-03-30 19:49:57 (GMT)
commit2b5ed373656c225d2baea09da130531fe7275fa2 (patch)
tree327717bda81b0494fa78107a3b995cbfb0338211 /chdir-notify.h
parentcb50761959c0c30aa9c44098db3a72db06570238 (diff)
add chdir-notify API
If one part of the code does a permanent chdir(), then this invalidates any relative paths that may be held by other parts of the code. For example, setup_work_tree() moves us to the top of the working tree, which may invalidate a previously stored relative gitdir. We've hacked around this case by teaching setup_work_tree() to re-run set_git_dir() with an adjusted path, but this stomps all over the idea of module boundaries. setup_work_tree() shouldn't have to know all of the places that need to be fed an adjusted path. And indeed, there's at least one other place (the refs code) which needs adjusting. Let's provide an API to let code that stores relative paths "subscribe" to updates to the current working directory. This means that callers of chdir() don't need to know about all subscribers ahead of time; they can simply consult a dynamically built list. Note that our helper function to reparent relative paths uses the simple remove_leading_path(). We could in theory use the much smarter relative_path(), but that led to some problems as described in 41894ae3a3 (Use simpler relative_path when set_git_dir, 2013-10-14). Since we're aiming to replace the setup_work_tree() code here, let's follow its lead. Signed-off-by: Jeff King <> Signed-off-by: Junio C Hamano <>
Diffstat (limited to 'chdir-notify.h')
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+ * 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 */