m_modules: make modreload work like restart

/modrestart used to be implemented as a normal command and could crash
when used remotely because it would reload m_encap, which was on the
call stack at the time. This was fixed in 41390bfe5f. However,
/modreload has exactly the same problem, so I'm giving it the
same treatment.

Incidentally: This bug was first discovered in ircd-seven, where the
`/mod*` commands themselves live in the core, so m_encap was the only way
the crash could happen (and it didn't most of the time, because m_encap
would only be moved if you got unlucky). But `/mod*` are in modules in
charybdis, so /modrestart would have unloaded the code it was in the
middle of executing. With that in mind, I'm not sure how it ever
appeared to work.

include/modules.h

@@ -28,6 +28,7 @@
 #include "defaults.h"
 #include "setup.h"
 #include "parse.h"
+#include "client.h" /* for IDLEN */
 
 #define MAPI_CHARYBDIS 2
 
@@ -118,6 +119,12 @@ struct mapi_mheader_av2
 #define DECLARE_MODULE_AV2(name, reg, unreg, cl, hl, hfnlist, caplist, v, desc) \
 	struct mapi_mheader_av2 _mheader = { MAPI_V2, reg, unreg, cl, hl, hfnlist, caplist, v, desc, DATECODE}
 
+struct modreload
+{
+	char module[BUFSIZE];
+	char id[IDLEN];
+};
+
 /* add a path */
 void mod_add_path(const char *path);
 void mod_clear_paths(void);

ircd/modules.c

@@ -36,6 +36,7 @@
 #include "match.h"
 #include "s_serv.h"
 #include "capability.h"
+#include "hash.h"
 
 #include <ltdl.h>
 
@@ -682,6 +683,49 @@ load_a_module(const char *path, bool warn, int origin, bool core)
 	return true;
 }
 
+void
+modules_do_reload(void *info_)
+{
+	struct modreload *info = info_;
+	struct module *mod;
+	int check_core;
+	char *m_bn = rb_basename(info->module);
+	struct Client *source_p = find_id(info->id);
+
+	if((mod = findmodule_byname(m_bn)) == NULL)
+	{
+		if (source_p) sendto_one_notice(source_p, ":Module %s is not loaded", m_bn);
+		rb_free(info);
+		rb_free(m_bn);
+		return;
+	}
+
+	check_core = mod->core;
+
+	mod_remember_clicaps();
+
+	if(unload_one_module(m_bn, true) == false)
+	{
+		if (source_p) sendto_one_notice(source_p, ":Module %s is not loaded", m_bn);
+		rb_free(info);
+		rb_free(m_bn);
+		return;
+	}
+
+	if((load_one_module(m_bn, mod->origin, check_core) == false) && check_core)
+	{
+		sendto_realops_snomask(SNO_GENERAL, L_NETWIDE,
+				     "Error reloading core module: %s: terminating ircd", m_bn);
+		ilog(L_MAIN, "Error loading core module %s: terminating ircd", m_bn);
+		exit(0);
+	}
+
+	mod_notify_clicaps();
+
+	rb_free(info);
+	rb_free(m_bn);
+}
+
 void
 modules_do_restart(void *unused)
 {

modules/core/m_modules.c

@@ -54,6 +54,7 @@ static void do_modreload(struct Client *, const char *);
 static void do_modlist(struct Client *, const char *);
 static void do_modrestart(struct Client *);
 
+extern void modules_do_reload(void *); /* end of ircd/modules.c */
 extern void modules_do_restart(void *); /* end of ircd/modules.c */
 
 struct Message modload_msgtab = {
@@ -317,39 +318,10 @@ do_modunload(struct Client *source_p, const char *module)
 static void
 do_modreload(struct Client *source_p, const char *module)
 {
-	struct module *mod;
-	int check_core;
-	char *m_bn = rb_basename(module);
-
-	if((mod = findmodule_byname(m_bn)) == NULL)
-	{
-		sendto_one_notice(source_p, ":Module %s is not loaded", m_bn);
-		rb_free(m_bn);
-		return;
-	}
-
-	check_core = mod->core;
-
-	mod_remember_clicaps();
-
-	if(unload_one_module(m_bn, true) == false)
-	{
-		sendto_one_notice(source_p, ":Module %s is not loaded", m_bn);
-		rb_free(m_bn);
-		return;
-	}
-
-	if((load_one_module(m_bn, mod->origin, check_core) == false) && check_core)
-	{
-		sendto_realops_snomask(SNO_GENERAL, L_NETWIDE,
-				     "Error reloading core module: %s: terminating ircd", m_bn);
-		ilog(L_MAIN, "Error loading core module %s: terminating ircd", m_bn);
-		exit(0);
-	}
-
-	mod_notify_clicaps();
-
-	rb_free(m_bn);
+	struct modreload *info = rb_malloc(sizeof *info);
+	strcpy(info->module, module);
+	strcpy(info->id, source_p->id);
+	rb_event_addonce("modules_do_reload", modules_do_reload, info, 1);
 }
 
 static void