MINOR: mux-quic: do not allocate Tx buf for empty STREAM frame

Sometimes it may be necessary to send an empty STREAM frame to signal
clean stream closure with FIN bit set. Prior to this change, a Tx buffer
was allocated unconditionnally even if no data is transferred.

Most of the times, allocation was not performed due to an older buffer
reused. But if data were already acknowledge, a new buffer is allocated.
No memory leak occurs as the buffer is properly released when the empty
frame acknowledge is received. But this allocation is unnecessary and it
consumes a connexion Tx buffer for nothing.

Improve this by skipping buffer allocation if no data to transfer.
qcs_build_stream_frm() is now able to deal with a NULL out argument.

This should be backported up to 2.6.

diff --git a/src/mux_quic.c b/src/mux_quic.c
index f4306e9056fb9908cdc177ade787d8e934363935..4019de5b927ec889022f8278a6d3cf402a11aded 100644 (file)
--- a/src/mux_quic.c
+++ b/src/mux_quic.c
@@ -1489,9 +1489,10 @@ static int qcs_xfer_data(struct qcs *qcs, struct buffer *out, struct buffer *in)
 
 /* Prepare a STREAM frame for <qcs> instance using <out> as payload. The frame
  * is appended in <frm_list>. Set <fin> if this is supposed to be the last
- * stream frame.
+ * stream frame. If <out> is NULL an empty STREAM frame is built : this may be
+ * useful if FIN needs to be sent without any data left.
  *
- * Returns the length of the STREAM frame or a negative error code.
+ * Returns the payload length of the STREAM frame or a negative error code.
  */
 static int qcs_build_stream_frm(struct qcs *qcs, struct buffer *out, char fin,
                                 struct list *frm_list)
@@ -1508,7 +1509,7 @@ static int qcs_build_stream_frm(struct qcs *qcs, struct buffer *out, char fin,
        BUG_ON(qcs->tx.sent_offset < base_off);
 
        head = qcs->tx.sent_offset - base_off;
-       total = b_data(out) - head;
+       total = out ? b_data(out) - head : 0;
        BUG_ON(total < 0);
 
        if (!total && !fin) {
@@ -1812,21 +1813,21 @@ static int _qc_send_qcs(struct qcs *qcs, struct list *frms)
        /* Cannot send STREAM on remote unidirectional streams. */
        BUG_ON(quic_stream_is_uni(qcs->id) && quic_stream_is_remote(qcc, qcs->id));
 
-       /* Allocate <out> buffer if necessary. */
-       if (!out) {
-               if (qcc->flags & QC_CF_CONN_FULL)
-                       goto out;
-
-               out = qc_stream_buf_alloc(qcs->stream, qcs->tx.offset);
+       if (b_data(buf)) {
+               /* Allocate <out> buffer if not already done. */
                if (!out) {
-                       TRACE_STATE("cannot allocate stream desc buffer", QMUX_EV_QCS_SEND, qcc->conn, qcs);
-                       qcc->flags |= QC_CF_CONN_FULL;
-                       goto out;
+                       if (qcc->flags & QC_CF_CONN_FULL)
+                               goto out;
+
+                       out = qc_stream_buf_alloc(qcs->stream, qcs->tx.offset);
+                       if (!out) {
+                               TRACE_STATE("cannot allocate stream desc buffer", QMUX_EV_QCS_SEND, qcc->conn, qcs);
+                               qcc->flags |= QC_CF_CONN_FULL;
+                               goto out;
+                       }
                }
-       }
 
-       /* Transfer data from <buf> to <out>. */
-       if (b_data(buf)) {
+               /* Transfer data from <buf> to <out>. */
                xfer = qcs_xfer_data(qcs, out, buf);
                if (xfer > 0) {
                        qcs_notify_send(qcs);
@@ -1837,10 +1838,10 @@ static int _qc_send_qcs(struct qcs *qcs, struct list *frms)
                BUG_ON_HOT(qcs->tx.offset > qcs->tx.msd);
                qcc->tx.offsets += xfer;
                BUG_ON_HOT(qcc->tx.offsets > qcc->rfctl.md);
-       }
 
-       /* out buffer cannot be emptied if qcs offsets differ. */
-       BUG_ON(!b_data(out) && qcs->tx.sent_offset != qcs->tx.offset);
+               /* out buffer cannot be emptied if qcs offsets differ. */
+               BUG_ON(!b_data(out) && qcs->tx.sent_offset != qcs->tx.offset);
+       }
 
        /* FIN is set if all incoming data were transferred. */
        fin = qcs_stream_fin(qcs);