config: dlopen() modules on-demand

TODO: optimizations and proper cleanup

* We currently reload the shared library for each *instance* of the
  module, and we do it twice; once when verifying, and once when
  instantiating.

* The shared libraries are never dlclosed()

config-verify.c

@@ -3,24 +3,17 @@
 #include <string.h>
 #include <assert.h>
 
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <dirent.h>
+#include <fcntl.h>
+#include <dlfcn.h>
+
 #define LOG_MODULE "config:verify"
 #define LOG_ENABLE_DBG 0
 #include "log.h"
 #include "tllist.h"
 
-#include "modules/alsa/alsa.h"
-#include "modules/backlight/backlight.h"
-#include "modules/battery/battery.h"
-#include "modules/clock/clock.h"
-#include "modules/i3/i3.h"
-#include "modules/label/label.h"
-#include "modules/label/label.h"
-#include "modules/mpd/mpd.h"
-#include "modules/network/network.h"
-#include "modules/removables/removables.h"
-#include "modules/xkb/xkb.h"
-#include "modules/xwindow/xwindow.h"
-
 const char *
 conf_err_prefix(const keychain_t *chain, const struct yml_node *node)
 {
@@ -441,42 +434,46 @@ verify_module(keychain_t *chain, const struct yml_node *node)
         return false;
     }
 
-    /* TODO: this will dlopened later */
-    static const struct {
-        const char *name;
-        const struct module_info *info;
-    } modules[] = {
-        {"alsa", &module_alsa},
-        {"backlight", &module_backlight},
-        {"battery", &module_battery},
-        {"clock", &module_clock},
-        {"i3", &module_i3},
-        {"label", &module_label},
-        {"mpd", &module_mpd},
-        {"network", &module_network},
-        {"removables", &module_removables},
-        {"xkb", &module_xkb},
-        {"xwindow", &module_xwindow},
-    };
+    char path[1024];
+    snprintf(path, sizeof(path), "./modules/lib%s.so", mod_name);
 
-    for (size_t i = 0; i < sizeof(modules) / sizeof(modules[0]); i++) {
-        if (strcmp(modules[i].name, mod_name) != 0)
-            continue;
+    void *lib = dlopen(path, RTLD_LOCAL | RTLD_NOW | RTLD_NOLOAD);
 
-        if (!conf_verify_dict(chain_push(chain, mod_name),
-                              values,
-                              modules[i].info->attrs,
-                              modules[i].info->attr_count))
-        {
-            return false;
-        }
+    if (lib == NULL)
+        lib = dlopen(path, RTLD_LOCAL | RTLD_NOW);
 
-        chain_pop(chain);
-        return true;
+    if (lib == NULL) {
+        const char *dl_error = dlerror();
+        if (dl_error != NULL)
+            LOG_ERR("%s: dlopen: %s", mod_name, dlerror());
+        else
+            LOG_ERR("%s: invalid module name: %s",
+                    conf_err_prefix(chain, module), mod_name);
+
+        return false;
     }
 
-    LOG_ERR("%s: invalid module name: %s", conf_err_prefix(chain, module), mod_name);
-    return false;
+    char sym[1024];
+    snprintf(sym, sizeof(sym), "module_%s", mod_name);
+
+    dlerror(); /* Clear previous error */
+    const struct module_info *info = dlsym(lib, sym);
+
+    const char *dlsym_error = dlerror();
+    if (dlsym_error != NULL) {
+        LOG_ERR("%s: dlsym: %s", mod_name, dlsym_error);
+        dlclose(lib);
+        return false;
+    }
+
+    assert(info != NULL);
+
+    if (!conf_verify_dict(chain_push(chain, mod_name), values,
+                          info->attrs, info->attr_count))
+        return false;
+
+    chain_pop(chain);
+    return true;
 }
 
 static bool
@@ -515,6 +512,45 @@ verify_bar_location(keychain_t *chain, const struct yml_node *node)
     return conf_verify_enum(chain, node, (const char *[]){"top", "bottom"}, 2);
 }
 
+#if defined(LOG_ENABLE_DBG) && LOG_ENABLE_DBG
+static void
+find_modules(void)
+{
+    int cwd = open(".", O_RDONLY);
+    assert(cwd != -1);
+
+    int modules = openat(cwd, "modules", O_RDONLY);
+    assert(modules != -1);
+
+    DIR *dir = fdopendir(modules);
+    assert(dir != NULL);
+
+    for (struct dirent *e = readdir(dir); e != NULL; e = readdir(dir)) {
+        const size_t len = strlen(e->d_name);
+
+        if (len <= 6) {
+            /* Need at least "libX.so" */
+            continue;
+        }
+
+        if (strncmp(e->d_name, "lib", 3) != 0)
+            continue;
+
+        if (strcmp(&e->d_name[len - 3], ".so") != 0)
+            continue;
+
+        char *name = malloc(len - 6 + 1);
+        memcpy(name, &e->d_name[3], len - 6);
+        name[len - 6] = '\0';
+
+        LOG_DBG("%s", name);
+        free(name);
+    }
+
+    closedir(dir);
+}
+#endif
+
 bool
 conf_verify_bar(const struct yml_node *bar)
 {
@@ -523,6 +559,10 @@ conf_verify_bar(const struct yml_node *bar)
         return false;
     }
 
+#if defined(LOG_ENABLE_DBG) && LOG_ENABLE_DBG
+    find_modules();
+#endif
+
     keychain_t chain = tll_init();
     chain_push(&chain, "bar");