Send a same-flow pure ACK heading a TX glom on its own (AmiNetXDuo #89)

src/glomsplit.h

@@ -0,0 +1,84 @@
+/*
+ * TX glom head split (AmiNetXDuo #89).  Pure: no Amiga headers, so the host
+ * test in tests/test_glomsplit.c builds it with cc.
+ *
+ * In a glom of three or more frames whose first two are pure ACKs of one TCP
+ * flow, the head ACK was absent from the peer's capture (A11: 21 of 21); in
+ * two-frame gloms of such a pair it was not (A11 0 of 44, G2 0 of 54).  Where
+ * it is lost after CMD53 is not established.  The driver never sends such a
+ * glom: it ends the glom after the pair, so a same-flow ACK run goes in pairs.
+ *
+ * Pure ACK: IPv4 (not a fragment, options allowed) or IPv6 (TCP as the first
+ * next header), TCP with no payload, ACK set, SYN, FIN and RST clear.  TCP
+ * options (timestamps, SACK) do not count as payload.  Same flow: equal
+ * source and destination addresses and ports.
+ */
+#ifndef WIFIPI_GLOMSPLIT_H
+#define WIFIPI_GLOMSPLIT_H
+
+/* frame: from the Ethernet header, len bytes; *key and *keyLen give the
+   address pair, *ports the port pair */
+static inline int wifipi_pure_ack(const unsigned char *f, unsigned long len,
+                                  const unsigned char **key, unsigned int *keyLen,
+                                  const unsigned char **ports)
+{
+    const unsigned char *ip = f + 14, *tcp;
+    unsigned long hl, iplen, thl;
+    unsigned int type;
+
+    if (f == 0 || len < 14 + 20) return 0;
+    type = (f[12] << 8) | f[13];
+
+    if (type == 0x0800)
+    {
+        if ((ip[0] >> 4) != 4 || ip[9] != 6) return 0;
+        if ((ip[6] & 0x3f) | ip[7]) return 0;               /* MF or offset */
+        hl = (ip[0] & 15) * 4;
+        iplen = (ip[2] << 8) | ip[3];
+        if (hl < 20) return 0;
+        *key = ip + 12; *keyLen = 8;
+    }
+    else if (type == 0x86dd)
+    {
+        if (len < 14 + 40 || (ip[0] >> 4) != 6 || ip[6] != 6) return 0;
+        hl = 40;
+        iplen = 40 + ((ip[4] << 8) | ip[5]);
+        *key = ip + 8; *keyLen = 32;
+    }
+    else return 0;
+
+    if (iplen < hl + 20 || 14 + iplen > len) return 0;
+    tcp = ip + hl;
+    thl = (tcp[12] >> 4) * 4;
+    if (thl < 20 || hl + thl != iplen) return 0;            /* payload */
+    if ((tcp[13] & 0x17) != 0x10) return 0;                 /* ACK; no FIN/SYN/RST */
+    *ports = tcp;
+    return 1;
+}
+
+/* frames[0..1] and lens[0..1]: the head of a glom of count frames */
+static inline int wifipi_glom_head_split(const unsigned char *const *frames,
+                                         const unsigned long *lens,
+                                         unsigned long count)
+{
+    const unsigned char *k0, *k1, *p0, *p1;
+    unsigned int n0, n1, i;
+
+    if (count < 3) return 0;
+    if (!wifipi_pure_ack(frames[0], lens[0], &k0, &n0, &p0)) return 0;
+    if (!wifipi_pure_ack(frames[1], lens[1], &k1, &n1, &p1)) return 0;
+    if (n0 != n1) return 0;
+    for (i = 0; i < n0; i++) if (k0[i] != k1[i]) return 0;
+    for (i = 0; i < 4; i++) if (p0[i] != p1[i]) return 0;
+    return 1;
+}
+
+/* frames the next transfer takes from a queue of count */
+static inline unsigned long wifipi_glom_take(const unsigned char *const *frames,
+                                             const unsigned long *lens,
+                                             unsigned long count)
+{
+    return wifipi_glom_head_split(frames, lens, count) ? 2 : count;
+}
+
+#endif

src/packet.c

@@ -20,6 +20,7 @@
 #include "wifipi.h"
 #include "packet.h"
 #include "brcm_wifi.h"
+#include "glomsplit.h"
 #include <aminetxduo/anxs2ext.h>
 
 #ifndef	PAD
@@ -1857,7 +1858,8 @@ void ProcessDataPacket(struct SDIO *sdio, UBYTE *packet, ULONG packetLength)
  * Byte 6~7: Reserved
  */
 
-int SendGlomDataPacket(struct SDIO *sdio, struct IOSana2Req **ioList, UBYTE count)
+/* one transfer from the head of ioList; returns the frames it took */
+static UBYTE SendGlomOnce(struct SDIO *sdio, struct IOSana2Req **ioList, UBYTE count)
 {
     struct WiFiBase *WiFiBase = sdio->s_WiFiBase;
     struct ExecBase *SysBase = sdio->s_SysBase;
@@ -1867,6 +1869,8 @@ int SendGlomDataPacket(struct SDIO *sdio, struct IOSana2Req **ioList, UBYTE coun
     struct PacketHeaderHW *pktBase = sdio->s_TXBuffer;
     UBYTE *byteBuffer = sdio->s_TXBuffer;
     struct GlomHeader *lastGh = NULL;
+    const UBYTE *head[2];
+    ULONG headLen[2];
 
     for (UBYTE i = 0; i < count; i++)
     {
@@ -1915,6 +1919,12 @@ int SendGlomDataPacket(struct SDIO *sdio, struct IOSana2Req **ioList, UBYTE coun
         *ptr++ = 0;
         *ptr++ = 0;
 
+        if (i < 2)
+        {
+            head[i] = ptr;
+            headLen[i] = packetLength - sizeof(struct Packet) - sizeof(struct GlomHeader) - 4;
+        }
+
         if ((io->ios2_Req.io_Flags & SANA2IOF_RAW) == 0)
         {
             // Copy destination
@@ -1956,6 +1966,14 @@ int SendGlomDataPacket(struct SDIO *sdio, struct IOSana2Req **ioList, UBYTE coun
             if (packetLength % 16 != 0) bug("\n");
         }
 #endif
+        /* two pure ACKs of one flow never head 3+: end the glom here, as
+           wifipi_glom_take() says (#89) */
+        if (i == 1 && wifipi_glom_head_split(head, headLen, count))
+        {
+            gh->gh_LastItem = 1;
+            count = 2;
+        }
+
         // Increase total length by packet length (aligned)
         totalLength += (packetLength + 3) & ~3;
     }
@@ -1998,6 +2016,19 @@ int SendGlomDataPacket(struct SDIO *sdio, struct IOSana2Req **ioList, UBYTE coun
         unit->wu_Stats.PacketsSent++;
     }
 
+    return count;
+}
+
+int SendGlomDataPacket(struct SDIO *sdio, struct IOSana2Req **ioList, UBYTE count)
+{
+    while (count)
+    {
+        UBYTE n = SendGlomOnce(sdio, ioList, count);
+
+        ioList += n;
+        count -= n;
+    }
+
     return 1;
 }