[or-cvs] r9321: Add some comments to TODO about nastiness of getting data-ch (in tor/trunk: . doc)

[nickm@xxxxxxxx]

Author: nickm
Date: 2007-01-10 14:49:11 -0500 (Wed, 10 Jan 2007)
New Revision: 9321

Modified:
   tor/trunk/
   tor/trunk/doc/TODO
Log:
 r11918@Kushana:  nickm | 2007-01-10 13:24:34 -0500
 Add some comments to TODO about nastiness of getting data-choking to work with directory bridges; propose a better solution for later, and some simpler solutions for now.



Property changes on: tor/trunk
___________________________________________________________________
 svk:merge ticket from /tor/trunk [r11918] on c95137ef-5f19-0410-b913-86e773d04f59

Modified: tor/trunk/doc/TODO
===================================================================
--- tor/trunk/doc/TODO	2007-01-10 16:33:56 UTC (rev 9320)
+++ tor/trunk/doc/TODO	2007-01-10 19:49:11 UTC (rev 9321)
@@ -68,7 +68,44 @@
       and use it when we're supposed to.
 N   - for tunneled edge conns, stop reading to the bridge connection
       when the or_conn we're writing to has a full outbuf.
+      - This is iffy.  Really, it would've been better to stop writing
+        on the dir conn when the edge conn's inbuf is getting full.
+        But the issue there is that we package from edge
+        connections aggressively until we hit their package windows or the
+        circuit package windows, even if the buffer on the corresponding OR
+        connection is pretty damn big.  This sucks from a RAM usage POV.
+        Now, we could try to stop reading on the edges (or just the edges
+        connected to a local bridge) when an or_conn's outbuf is full.  But
+        if we're a server, and we stop reading on some exit conns when OR
+        conns are full, soon OR conns will contain only traffic from other OR
+        conns, and the exit data in question  will never get written.
 
+      - The right solution in the long run (0.2.0) is probably as follows:
+        - Remove socketpair-based bridges: use shared (or connected) buffers
+          for communication, rather than sockets.
+        - When relaying cells from an OR conn to an OR conn, have them wait
+          in a queue on the or_circuit_t object; don't move them onto the
+          target conn until there is space in the target conn's outbuf.
+          Also, only package data from exitconns when there is space in the
+          target conn's outbuf.
+          - As an added advantage, this would let us kill stalled _circuits_
+            when their buffers get too full, rather than killing entire OR
+            conns.  But we must think about anonymity implications of that.
+        - We'll probably want to do some kind of big refactoring of our
+          dataflow when we do these changes; stuff is hairy enough already,
+          and it will only get harrier with this stuff.
+
+      - For the short run, our options seem to be:
+        - Disable BEGIN_DIR support at the server-side unless it's
+          explicitly turned on.
+        - Go ahead and make directory bridge data not get produced when the
+          corresponding or_conn is full, and accept the sometimes directory
+          data will just never get written.
+        - Rate-limit directory bridge data somehow when the corresponding
+          or_conn is full.  Possibly based on the flush rate of the or_conn?
+        - Reject BEGIN_DIR requests that we think will be insanely big.
+
+
 N - DNS improvements
     . Asynchronous DNS
       - Make evdns use windows strerror equivalents.