dccp ccid-3: remove buggy RTT-sampling history lookup

This removes the RTT-sampling function tfrc_tx_hist_rtt(), since

 1. it suffered from complex passing of return values (the return value both
    indicated successful lookup while the value doubled as RTT sample);

 2. when for some odd reason the sample value equalled 0, this triggered a bug
    warning about "bogus Ack", due to the ambiguity of the return value;

 3. on a passive host which has not sent anything the TX history is empty and
    thus will lead to unwanted "bogus Ack" warnings such as
    ccid3_hc_tx_packet_recv: server(e7b7d518): DATAACK with bogus ACK-28197148
    ccid3_hc_tx_packet_recv: server(e7b7d518): DATAACK with bogus ACK-26641606.

The fix is to replace the implicit encoding by performing the steps manually.

Furthermore, the "bogus Ack" warning has been removed, since it can actually be
triggered due to several reasons (network reordering, old packet, (3) above),
hence it is not very useful.

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>

2 files changed, 19 insertions, 42 deletions

diff --git a/net/dccp/ccids/lib/packet_history.c b/net/dccp/ccids/lib/packet_history.c
index 3a4f414e94a0..de8fe294bf0b 100644
--- a/net/dccp/ccids/lib/packet_history.c
+++ b/net/dccp/ccids/lib/packet_history.c
@@ -38,18 +38,6 @@
 #include "packet_history.h"
 #include "../../dccp.h"
 
-/**
- *  tfrc_tx_hist_entry  -  Simple singly-linked TX history list
- *  @next:  next oldest entry (LIFO order)
- *  @seqno: sequence number of this entry
- *  @stamp: send time of packet with sequence number @seqno
- */
-struct tfrc_tx_hist_entry {
-        struct tfrc_tx_hist_entry *next;
-        u64                       seqno;
-        ktime_t                   stamp;
-};
-
 /*
  * Transmitter History Routines
  */
@@ -71,15 +59,6 @@ void tfrc_tx_packet_history_exit(void)
         }
 }
 
-static struct tfrc_tx_hist_entry *
-        tfrc_tx_hist_find_entry(struct tfrc_tx_hist_entry *head, u64 seqno)
-{
-        while (head != NULL && head->seqno != seqno)
-                head = head->next;
-
-        return head;
-}
-
 int tfrc_tx_hist_add(struct tfrc_tx_hist_entry **headp, u64 seqno)
 {
         struct tfrc_tx_hist_entry *entry = kmem_cache_alloc(tfrc_tx_hist_slab, gfp_any());
@@ -107,24 +86,6 @@ void tfrc_tx_hist_purge(struct tfrc_tx_hist_entry **headp)
         *headp = NULL;
 }
 
-u32 tfrc_tx_hist_rtt(struct tfrc_tx_hist_entry *head, const u64 seqno,
-                     const ktime_t now)
-{
-        u32 rtt = 0;
-        struct tfrc_tx_hist_entry *packet = tfrc_tx_hist_find_entry(head, seqno);
-
-        if (packet != NULL) {
-                rtt = ktime_us_delta(now, packet->stamp);
-                /*
-                 * Garbage-collect older (irrelevant) entries:
-                 */
-                tfrc_tx_hist_purge(&packet->next);
-        }
-
-        return rtt;
-}
-
-
 /*
  *      Receiver History Routines
  */
diff --git a/net/dccp/ccids/lib/packet_history.h b/net/dccp/ccids/lib/packet_history.h
index 7df6c5299999..7ee4a9d9d335 100644
--- a/net/dccp/ccids/lib/packet_history.h
+++ b/net/dccp/ccids/lib/packet_history.h
@@ -40,12 +40,28 @@
 #include <linux/slab.h>
 #include "tfrc.h"
 
-struct tfrc_tx_hist_entry;
+/**
+ *  tfrc_tx_hist_entry  -  Simple singly-linked TX history list
+ *  @next:  next oldest entry (LIFO order)
+ *  @seqno: sequence number of this entry
+ *  @stamp: send time of packet with sequence number @seqno
+ */
+struct tfrc_tx_hist_entry {
+        struct tfrc_tx_hist_entry *next;
+        u64                       seqno;
+        ktime_t                   stamp;
+};
+
+static inline struct tfrc_tx_hist_entry *
+        tfrc_tx_hist_find_entry(struct tfrc_tx_hist_entry *head, u64 seqno)
+{
+        while (head != NULL && head->seqno != seqno)
+                head = head->next;
+        return head;
+}
 
 extern int  tfrc_tx_hist_add(struct tfrc_tx_hist_entry **headp, u64 seqno);
 extern void tfrc_tx_hist_purge(struct tfrc_tx_hist_entry **headp);
-extern u32  tfrc_tx_hist_rtt(struct tfrc_tx_hist_entry *head,
-                             const u64 seqno, const ktime_t now);
 
 /* Subtraction a-b modulo-16, respects circular wrap-around */
 #define SUB16(a, b) (((a) + 16 - (b)) & 0xF)