From 4c6c21f92a8204abf031e42bb4949a0ecf039f7a Mon Sep 17 00:00:00 2001
From: David Herrmann <dh.herrmann@gmail.com>
Date: Wed, 11 Mar 2015 13:53:21 +0100
Subject: [PATCH] bus-proxy: complain only once about queue overflows

If the local peer does not dispatch its incoming queue, the bus-proxy will
slowly fill its outgoing queue. Once its full, it will continously
complain that it cannot forward its messages.

As it turns out, pulseaudio does have an idle background dbus connection
that is not integrated into any mainloop (and given that gdbus and
libdbus1 both support background shared connections, PA is probably not
the only example), therefore, the bus-proxy will loudly complain if it
cannot forward NameOwnerChanged events once the queue is full.

This commit makes the proxy track queue-state and complain only once the
queue runs full, not if it is already full.

A PA bug-report (and patch) has been filed, and other applications should
be fixed similarly. Hence, lets keep the error message, instead of
dropping it. It's unused resources we really want to get rid of, so
silencing the message does not really help (which is actually what
dbus-daemon does).

(cherry picked from commit ec2c7b56599981a7d9e76b15c75af3e1af3e6f81)
---
 src/bus-proxyd/proxy.c | 16 ++++++++++++----
 src/bus-proxyd/proxy.h |  1 +
 2 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/src/bus-proxyd/proxy.c b/src/bus-proxyd/proxy.c
index 3dea908f5..e13cf5e2e 100644
--- a/src/bus-proxyd/proxy.c
+++ b/src/bus-proxyd/proxy.c
@@ -729,13 +729,21 @@ static int proxy_process_destination_to_local(Proxy *p) {
 
                 /* Return the error to the client, if we can */
                 synthetic_reply_method_errnof(m, r, "Failed to forward message we got from destination: %m");
-                log_error_errno(r,
-                         "Failed to forward message we got from destination: uid=" UID_FMT " gid=" GID_FMT" message=%s destination=%s path=%s interface=%s member=%s: %m",
-                         p->local_creds.uid, p->local_creds.gid, bus_message_type_to_string(m->header->type),
-                         strna(m->destination), strna(m->path), strna(m->interface), strna(m->member));
+                if (r == -ENOBUFS) {
+                        /* if local dbus1 peer does not dispatch its queue, warn only once */
+                        if (!p->queue_overflow)
+                                log_error("Dropped messages due to queue overflow of local peer (pid: "PID_FMT" uid: "UID_FMT")", p->local_creds.pid, p->local_creds.uid);
+                        p->queue_overflow = true;
+                } else
+                        log_error_errno(r,
+                                 "Failed to forward message we got from destination: uid=" UID_FMT " gid=" GID_FMT" message=%s destination=%s path=%s interface=%s member=%s: %m",
+                                 p->local_creds.uid, p->local_creds.gid, bus_message_type_to_string(m->header->type),
+                                 strna(m->destination), strna(m->path), strna(m->interface), strna(m->member));
+
                 return 1;
         }
 
+        p->queue_overflow = false;
         return 1;
 }
 
diff --git a/src/bus-proxyd/proxy.h b/src/bus-proxyd/proxy.h
index 913d47071..782c4e60b 100644
--- a/src/bus-proxyd/proxy.h
+++ b/src/bus-proxyd/proxy.h
@@ -40,6 +40,7 @@ struct Proxy {
         SharedPolicy *policy;
 
         bool got_hello : 1;
+        bool queue_overflow : 1;
 };
 
 int proxy_new(Proxy **out, int in_fd, int out_fd, const char *dest);