Provide generic mechanism for scheduler to query writeable cells on a channel

src/or/channel.c

@@ -3826,6 +3826,40 @@ channel_mark_outgoing(channel_t *chan)
   chan->is_incoming = 0;
 }
 
+/************************
+ * Flow control queries *
+ ***********************/
+
+/*
+ * Estimate the number of writeable cells
+ *
+ * Ask the lower layer for an estimate of how many cells it can accept, and
+ * then subtract the length of our outgoing_queue, if any, to produce an
+ * estimate of the number of cells this channel can accept for writes.
+ */
+
+int
+channel_num_cells_writeable(channel_t *chan)
+{
+  int result;
+
+  tor_assert(chan);
+  tor_assert(chan->num_cells_writeable);
+
+  if (chan->state == CHANNEL_STATE_OPEN) {
+    /* Query lower layer */
+    result = chan->num_cells_writeable(chan);
+    /* Subtract cell queue length, if any */
+    result -= chan_cell_queue_len(&chan->outgoing_queue);
+    if (result < 0) result = 0;
+  } else {
+    /* No cells are writeable in any other state */
+    result = 0;
+  }
+
+  return result;
+}
+
 /*********************
  * Timestamp updates *
  ********************/

src/or/channel.h

@@ -110,7 +110,9 @@ struct channel_s {
   int (*matches_extend_info)(channel_t *, extend_info_t *);
   /** Check if this channel matches a target address when extending */
   int (*matches_target)(channel_t *, const tor_addr_t *);
-  /** Write a cell to an open channel */
+  /* Ask the lower layer how many cells can be written */
+  int (*num_cells_writeable)(channel_t *);
+  /* Write a cell to an open channel */
   int (*write_cell)(channel_t *, cell_t *);
   /** Write a packed cell to an open channel */
   int (*write_packed_cell)(channel_t *, packed_cell_t *);
@@ -465,6 +467,9 @@ void channel_listener_dump_statistics(channel_listener_t *chan_l,
 void channel_listener_dump_transport_statistics(channel_listener_t *chan_l,
                                                 int severity);
 
+/* Flow control queries */
+int channel_num_cells_writeable(channel_t *chan);
+
 /* Timestamp queries */
 time_t channel_when_created(channel_t *chan);
 time_t channel_when_last_active(channel_t *chan);

src/or/channeltls.c

@@ -68,6 +68,7 @@ channel_tls_matches_extend_info_method(channel_t *chan,
                                        extend_info_t *extend_info);
 static int channel_tls_matches_target_method(channel_t *chan,
                                              const tor_addr_t *target);
+static int channel_tls_num_cells_writeable_method(channel_t *chan);
 static int channel_tls_write_cell_method(channel_t *chan,
                                          cell_t *cell);
 static int channel_tls_write_packed_cell_method(channel_t *chan,
@@ -124,6 +125,7 @@ channel_tls_common_init(channel_tls_t *tlschan)
   chan->is_canonical = channel_tls_is_canonical_method;
   chan->matches_extend_info = channel_tls_matches_extend_info_method;
   chan->matches_target = channel_tls_matches_target_method;
+  chan->num_cells_writeable = channel_tls_num_cells_writeable_method;
   chan->write_cell = channel_tls_write_cell_method;
   chan->write_packed_cell = channel_tls_write_packed_cell_method;
   chan->write_var_cell = channel_tls_write_var_cell_method;
@@ -673,6 +675,34 @@ channel_tls_matches_target_method(channel_t *chan,
   return tor_addr_eq(&(tlschan->conn->real_addr), target);
 }
 
+/**
+ * Tell the upper layer how many cells we can accept to write
+ *
+ * This implements the num_cells_writeable method for channel_tls_t; it
+ * returns an estimate of the number of cells we can accept with
+ * channel_tls_write_*_cell().
+ */
+
+static int
+channel_tls_num_cells_writeable_method(channel_t *chan)
+{
+  size_t outbuf_len;
+  int n;
+  channel_tls_t *tlschan = BASE_CHAN_TO_TLS(chan);
+  size_t cell_network_size;
+
+  tor_assert(tlschan);
+  tor_assert(tlschan->conn);
+
+  cell_network_size = get_cell_network_size(tlschan->conn->wide_circ_ids);
+  outbuf_len = connection_get_outbuf_len(TO_CONN(tlschan->conn));
+  /* Get the number of cells */
+  n = CEIL_DIV(OR_CONN_HIGHWATER - outbuf_len, cell_network_size);
+  if (n < 0) n = 0;
+
+  return n;
+}
+
 /**
  * Write a cell to a channel_tls_t
  *

src/or/connection_or.c

@@ -576,14 +576,6 @@ connection_or_process_inbuf(or_connection_t *conn)
   return ret;
 }
 
-/** When adding cells to an OR connection's outbuf, keep adding until the
- * outbuf is at least this long, or we run out of cells. */
-#define OR_CONN_HIGHWATER (32*1024)
-
-/** Add cells to an OR connection's outbuf whenever the outbuf's data length
- * drops below this size. */
-#define OR_CONN_LOWWATER (16*1024)
-
 /** Called whenever we have flushed some data on an or_conn: add more data
  * from active circuits. */
 int

src/or/or.h

@@ -1426,6 +1426,18 @@ typedef struct or_handshake_state_t {
 
 /** Length of Extended ORPort connection identifier. */
 #define EXT_OR_CONN_ID_LEN DIGEST_LEN /* 20 */
+/*
+ * OR_CONN_HIGHWATER and OR_CONN_LOWWATER moved from connection_or.c so
+ * channeltls.c can see them too.
+ */
+
+/** When adding cells to an OR connection's outbuf, keep adding until the
+ * outbuf is at least this long, or we run out of cells. */
+#define OR_CONN_HIGHWATER (32*1024)
+
+/** Add cells to an OR connection's outbuf whenever the outbuf's data length
+ * drops below this size. */
+#define OR_CONN_LOWWATER (16*1024)
 
 /** Subtype of connection_t for an "OR connection" -- that is, one that speaks
  * cells over TLS. */

src/or/scheduler.c

@@ -324,6 +324,7 @@ void
 scheduler_run(void)
 {
   smartlist_t *tmp = NULL;
+  int n_cells;
 
   log_debug(LD_SCHED, "We have a chance to run the scheduler");
 
@@ -337,9 +338,18 @@ scheduler_run(void)
   channels_pending = smartlist_new();
 
   SMARTLIST_FOREACH_BEGIN(tmp, channel_t *, chan) {
-    log_debug(LD_SCHED,
-              "Scheduler saw pending channel " U64_FORMAT " at %p",
-              U64_PRINTF_ARG(chan->global_identifier), chan);
+    n_cells = channel_num_cells_writeable(chan);
+    if (n_cells > 0) {
+      log_debug(LD_SCHED,
+                "Scheduler saw pending channel " U64_FORMAT " at %p with "
+                "%d cells writeable",
+                U64_PRINTF_ARG(chan->global_identifier), chan, n_cells);
+    } else {
+      log_info(LD_SCHED,
+               "Scheduler saw pending channel " U64_FORMAT " at %p with "
+               "no cells writeable",
+               U64_PRINTF_ARG(chan->global_identifier), chan);
+    }
   } SMARTLIST_FOREACH_END(chan);
 
   smartlist_free(tmp);