MINOR: proxy: add refcount to proxies

Implement refcount notion into proxy structure. The objective is to be
able to increment refcount on proxy to prevent its deletion temporarily.
This is similar to the server refcount : "del backend" is not blocked
and will remove the targetted instance from the global proxies_list.
However, the final free operation is delayed until the refcount is null.

As stated above, the API is similar to servers. Proxies are initialized
with a refcount of 1. Refcount can be incremented via proxy_take(). When
no longer useful, refcount is decremented via proxy_drop() which
replaces the older free_proxy(). Deinit is only performed once refcount
is null.

This commit also defines flag PR_FL_DELETED. It is set when a proxy
instance has been removed via a "del backend" CLI command. This should
serve as indication to modules which may still have a refcount on the
target proxy so that they can release it as soon as possible.

Note that this new refcount is completely ignored for a default proxy
instance. For them, proxy_take() is pure noop. Free is immediately
performed on first proxy_drop() invokation.

include/haproxy/proxy-t.h

@@ -247,6 +247,7 @@ enum PR_SRV_STATE_FILE {
 #define PR_FL_PAUSED             0x00000020  /* The proxy was paused at run time (reversible) */
 #define PR_FL_CHECKED            0x00000040  /* The proxy configuration was fully checked (including postparsing checks) */
 #define PR_FL_BE_UNPUBLISHED     0x00000080  /* The proxy cannot be targetted by content switching rules */
+#define PR_FL_DELETED            0x00000100  /* Proxy has been deleted and must be manipulated with care */
 
 struct stream;
 
@@ -508,6 +509,7 @@ struct proxy {
 
 	struct guid_node guid;			/* GUID global tree node */
 	struct mt_list watcher_list;		/* list of elems which currently references this proxy instance (currently only used with backends) */
+	uint refcount;				/* refcount to keep proxy from being deleted during runtime */
 
 	EXTRA_COUNTERS(extra_counters_fe);
 	EXTRA_COUNTERS(extra_counters_be);

include/haproxy/proxy.h

@@ -58,7 +58,7 @@ void stop_proxy(struct proxy *p);
 int  stream_set_backend(struct stream *s, struct proxy *be);
 
 void deinit_proxy(struct proxy *p);
-void free_proxy(struct proxy *p);
+void proxy_drop(struct proxy *p);
 const char *proxy_cap_str(int cap);
 const char *proxy_mode_str(int mode);
 enum pr_mode str_to_proxy_mode(const char *mode);
@@ -82,6 +82,7 @@ void proxy_unref_defaults(struct proxy *px);
 int setup_new_proxy(struct proxy *px, const char *name, unsigned int cap, char **errmsg);
 struct proxy *alloc_new_proxy(const char *name, unsigned int cap,
                               char **errmsg);
+void proxy_take(struct proxy *px);
 struct proxy *parse_new_proxy(const char *name, unsigned int cap,
                               const char *file, int linenum,
                               const struct proxy *defproxy);

src/haproxy.c

@@ -2814,7 +2814,7 @@ void deinit(void)
 	while (p) {
 		p0 = p;
 		p = p->next;
-		free_proxy(p0);
+		proxy_drop(p0);
 	}/* end while(p) */
 
 	/* we don't need to free sink_proxies_list nor cfg_log_forward proxies since

src/hlua.c

@@ -14726,7 +14726,7 @@ static void hlua_deinit()
 			lua_close(hlua_states[thr]);
 	}
 
-	free_proxy(socket_proxy);
+	proxy_drop(socket_proxy);
 }
 
 REGISTER_POST_DEINIT(hlua_deinit);

src/http_client.c

@@ -1214,7 +1214,7 @@ err:
 	if (err_code & ERR_CODE) {
 		ha_alert("httpclient: cannot initialize: %s\n", errmsg);
 		free(errmsg);
-		free_proxy(px);
+		proxy_drop(px);
 
 		return NULL;
 	}

src/log.c

@@ -3739,7 +3739,7 @@ void deinit_log_forward()
 	while (p) {
 		p0 = p;
 		p = p->next;
-		free_proxy(p0);
+		proxy_drop(p0);
 	}
 }
 

src/proxy.c

@@ -456,9 +456,19 @@ void deinit_proxy(struct proxy *p)
 	proxy_unref_defaults(p);
 }
 
-/* deinit and free <p> proxy */
-void free_proxy(struct proxy *p)
+/* Decrement <p> refcount and free it if null. For a default proxy instance,
+ * refcount is ignored and free is immediately performed.
+ */
+void proxy_drop(struct proxy *p)
 {
+	if (!p)
+		return;
+
+	if (!(p->cap & PR_CAP_DEF)) {
+		if (HA_ATOMIC_SUB_FETCH(&p->refcount, 1))
+			return;
+	}
+
 	deinit_proxy(p);
 	ha_free(&p);
 }
@@ -3211,6 +3221,8 @@ struct proxy *alloc_new_proxy(const char *name, unsigned int cap, char **errmsg)
 	if (!setup_new_proxy(curproxy, name, cap, errmsg))
 		goto fail;
 
+	proxy_take(curproxy);
+
  done:
 	return curproxy;
 
@@ -3225,6 +3237,13 @@ struct proxy *alloc_new_proxy(const char *name, unsigned int cap, char **errmsg)
 	return NULL;
 }
 
+/* Increment <px> refcount. Does nothing for a default proxy instance. */
+void proxy_take(struct proxy *px)
+{
+	if (!(px->cap & PR_CAP_DEF))
+		HA_ATOMIC_INC(&px->refcount);
+}
+
 /* post-check for proxies */
 static int proxy_postcheck(struct proxy *px)
 {
@@ -4955,8 +4974,8 @@ static int cli_parse_add_backend(char **args, char *payload, struct appctx *appc
 	return 1;
 
  err:
-	/* free_proxy() ensures any potential refcounting on defpx is decremented. */
-	free_proxy(px);
+	/* This ensures any potential refcounting on defpx is decremented. */
+	proxy_drop(px);
 	thread_release();
 
 	if (msg) {
@@ -5053,6 +5072,8 @@ static int cli_parse_delete_backend(char **args, char *payload, struct appctx *a
 		goto out;
 	}
 
+	px->flags |= PR_FL_DELETED;
+
 	thread_release();
 
 	ha_notice("Backend deleted.\n");

src/resolvers.c

@@ -2637,7 +2637,7 @@ static void resolvers_destroy(struct resolvers *resolvers)
 		resolv_free_resolution(res);
 	}
 
-	free_proxy(resolvers->px);
+	proxy_drop(resolvers->px);
 	free(resolvers->id);
 	free((char *)resolvers->conf.file);
 	task_destroy(resolvers->t);
@@ -3586,7 +3586,7 @@ out:
 err_free_conf_file:
 	ha_free((void **)&r->conf.file);
 err_free_p:
-	free_proxy(p);
+	proxy_drop(p);
 err_free_r:
 	ha_free(&r);
 	return err_code;

src/sink.c

@@ -818,7 +818,7 @@ static void sink_free(struct sink *sink)
 	}
 	LIST_DEL_INIT(&sink->sink_list); // remove from parent list
 	task_destroy(sink->forward_task);
-	free_proxy(sink->forward_px);
+	proxy_drop(sink->forward_px);
 	ha_free(&sink->name);
 	ha_free(&sink->desc);
 	while (sink->sft) {
@@ -866,7 +866,7 @@ static struct sink *sink_new_ringbuf(const char *id, const char *description,
 	return sink;
 
  err:
-	free_proxy(p);
+	proxy_drop(p);
 	return NULL;
 }