svm: store normalized head/tail for fifo

If head/tail are stored as "absolute" values that are normalized to [0,
fifo_size] interval, when fifo is shrunk/grown the consumer and producer
have to independently update to the new fifo size and fix head and tail,
respectively.

If the head and tail are stored as normalized values, under the right
conditions, they don't need to be fixed when fifo size changes.

This reverts one of the changes in gerrit 18223.

Change-Id: I55a908828afe90925cf7c20186a940b25e5805f9
Signed-off-by: Florin Coras <fcoras@cisco.com>

1 files changed, 7 insertions, 2 deletions

diff --git a/src/plugins/unittest/svm_fifo_test.c b/src/plugins/unittest/svm_fifo_test.c
index 99f0e5044d6..d2afc36e0d0 100644
--- a/src/plugins/unittest/svm_fifo_test.c
+++ b/src/plugins/unittest/svm_fifo_test.c
@@ -806,7 +806,7 @@ sfifo_test_fifo4 (vlib_main_t * vm, unformat_input_t * input)
 static u32
 fifo_pos (svm_fifo_t * f, u32 pos)
 {
-  return pos;
+  return pos % f->size;
 }
 
 /* Avoids exposing svm_fifo.c internal function */
@@ -1194,6 +1194,7 @@ sfifo_test_fifo_grow (vlib_main_t * vm, unformat_input_t * input)
   svm_fifo_chunk_t *c, *next, *prev;
   u8 *test_data = 0, *data_buf = 0;
   svm_fifo_t *f;
+  u32 old_tail;
 
   while (unformat_check_input (input) != UNFORMAT_END_OF_INPUT)
     {
@@ -1288,10 +1289,14 @@ sfifo_test_fifo_grow (vlib_main_t * vm, unformat_input_t * input)
   SFIFO_TEST (f->size == fifo_size + 200, "size expected %u is %u",
 	      fifo_size + 200, f->size);
 
-  svm_fifo_dequeue (f, 201, data_buf);
+  old_tail = f->tail;
+  svm_fifo_dequeue (f, 101, data_buf);
 
   SFIFO_TEST (f->size == fifo_size + 200 + 10 * 100, "size expected %u is %u",
 	      fifo_size + 200 + 10 * 100, f->size);
+  SFIFO_TEST (f->tail == old_tail, "new tail expected %u is %u", old_tail,
+	      f->tail);
+
   /*
    * Enqueue/dequeue tests
    */