conf: fix reloading on IN_CREATE

If the config file is a symlink, wayfire attempts to watch the parent
directory so that, if replaced via a subsequent `ln -sf`, it'll still
be notified. When notified, however, wayfire doesn't immediately
reload the config file. Rather, as this event may be triggered by any
file creation in the directory, we first make sure that the config file
really is the one being created anew.

The filename from inotify is stored as a flexible array member in the
event struct, though, and this was somehow causing problems when
compared with the known std::string basename.

Fixes #2210.

src/default-config-backend.cpp

@@ -7,6 +7,7 @@
 #include <wayfire/plugin.hpp>
 #include <wayfire/core.hpp>
 
+#include <cstring>
 #include <sys/inotify.h>
 #include <filesystem>
 #include <unistd.h>
@@ -58,18 +59,22 @@ static int handle_config_updated(int fd, uint32_t mask, void *data)
          ptr += sizeof(inotify_event) + event->len)
     {
         event = reinterpret_cast<inotify_event*>(ptr);
-        // We reload in two main cases:
+        // We reload in two cases:
         //
-        // - Config file itself was modified
-        // - Config file was created inside parent directory
-        should_reload |=
-            (event->wd == wd_cfg_file) || (cfg_file_basename == event->name);
+        // 1. The config file itself was modified, or...
+        should_reload |= event->wd == wd_cfg_file;
+        // 2. The config file was moved/created inside the parent directory.
+        if (event->len > 0) {
+            // This is UB unless event->len > 0.
+            auto name_matches = strcmp(cfg_file_basename.c_str(), event->name);
+
+            if (name_matches) {
+                inotify_rm_watch(fd, wd_cfg_file);
+                wd_cfg_file =
+                    inotify_add_watch(fd, (config_dir + "/" + cfg_file_basename).c_str(), IN_CLOSE_WRITE);
+            }
 
-        if ((event->name == cfg_file_basename) && (event->wd == wd_cfg_dir))
-        {
-            inotify_rm_watch(fd, wd_cfg_file);
-            wd_cfg_file =
-                inotify_add_watch(fd, (config_dir + "/" + cfg_file_basename).c_str(), IN_CLOSE_WRITE);
+            should_reload |= name_matches;
         }
     }