diff --git a/docs/logging.md b/docs/logging.md
index e1140c3..3cbc957 100644
--- a/docs/logging.md
+++ b/docs/logging.md
@@ -12,12 +12,14 @@ timestamps or exact transfer sizes. The ``--blur-usage=`` option enables
 this, and it takes an integer value (in seconds) to specify the desired time
 window.
 
-## Logging JSON to stdout
+## Logging JSON Upon Each Connection
 
-If --log-stdout is provided, a line will be written to stdout after each
-connection is done. This line will be a complete JSON object (starting with
-``{``, ending with ``}\n``, and containing no internal newlines). The keys
-will be:
+If --log-fd is provided, a line will be written to the given (numeric) file
+descriptor after each connection is done. These events could be delivered to
+a comprehensive logging system like XXX for offline analysis.
+
+Each line will be a complete JSON object (starting with ``{``, ending with
+``}\n``, and containing no internal newlines). The keys will be:
 
 * ``started``: number, seconds since epoch
 * ``total_time``: number, seconds from open to last close
@@ -30,7 +32,11 @@ means a second matching side never appeared (and thus ``waiting_time`` will
 be null). ``errory`` means the first side gave an invalid handshake.
 
 If --blur-usage= is provided, then ``started`` will be rounded to the given
-time interval, and ``total_bytes`` will be rounded as well.
+time interval, and ``total_bytes`` will be rounded to a fixed set of buckets:
+
+* file sizes less than 1MB: rounded to the next largest multiple of 10kB
+* less than 1GB: multiple of 1MB
+* 1GB or larger: multiple of 100MB
 
 ## Usage Database
 
@@ -77,5 +83,9 @@ the ``current`` table will be updated at least once every 5 minutes.
 
 If daemonized by twistd, the server will write ``twistd.pid`` and
 ``twistd.log`` files as usual. By default ``twistd.log`` will only contain
-startup, shutdown, and exception messages. Adding --log-stdout will add
-per-connection JSON lines to ``twistd.log``.
+startup, shutdown, and exception messages.
+
+Setting ``--log-fd=1`` (file descriptor 1 is always stdout) will cause the
+per-connection JSON lines to be interleaved with any messages sent to
+Twisted's logging system. It may be better to use a different file
+descriptor.
diff --git a/src/wormhole_transit_relay/server_tap.py b/src/wormhole_transit_relay/server_tap.py
index c4223c0..0f7ca50 100644
--- a/src/wormhole_transit_relay/server_tap.py
+++ b/src/wormhole_transit_relay/server_tap.py
@@ -1,4 +1,4 @@
-import sys
+import os
 from . import transit_server
 from twisted.internet import reactor
 from twisted.python import usage
@@ -14,15 +14,13 @@ glues the two TCP sockets together.
 """
 
 class Options(usage.Options):
-    synopsis = "[--port=] [--log-stdout] [--blur-usage=] [--usage-db=]"
+    synopsis = "[--port=] [--log-fd] [--blur-usage=] [--usage-db=]"
     longdesc = LONGDESC
 
-    optFlags = {
-        ("log-stdout", None, "write JSON usage logs to stdout"),
-        }
     optParameters = [
         ("port", "p", "tcp:4001", "endpoint to listen on"),
         ("blur-usage", None, None, "blur timestamps and data sizes in logs"),
+        ("log-fd", None, None, "write JSON usage logs to this file descriptor"),
         ("usage-db", None, None, "record usage data (SQLite)"),
         ]
 
@@ -32,7 +30,9 @@ class Options(usage.Options):
 
 def makeService(config, reactor=reactor):
     ep = endpoints.serverFromString(reactor, config["port"]) # to listen
-    log_file = sys.stdout if config["log-stdout"] else None
+    log_file = (os.fdopen(int(config["log-fd"]), "w")
+                if config["log-fd"] is not None
+                else None)
     f = transit_server.Transit(blur_usage=config["blur-usage"],
                                log_file=log_file,
                                usage_db=config["usage-db"])