vcl svm: provide apps access to fifo chunks

Type: feature

Signed-off-by: Florin Coras <fcoras@cisco.com>
Change-Id: I2191b8594b1e87ecc00f237316457db249f73603

2 files changed, 36 insertions, 31 deletions

diff --git a/src/svm/svm_fifo.c b/src/svm/svm_fifo.c
index fda9481e721..2cce2bf50b3 100644
--- a/src/svm/svm_fifo.c
+++ b/src/svm/svm_fifo.c
@@ -1136,9 +1136,11 @@ svm_fifo_fill_chunk_list (svm_fifo_t * f)
 }
 
 int
-svm_fifo_segments (svm_fifo_t * f, svm_fifo_seg_t * fs)
+svm_fifo_segments (svm_fifo_t * f, svm_fifo_seg_t * fs, u32 n_segs,
+		   u32 max_bytes)
 {
-  u32 cursize, head, tail, head_idx;
+  u32 cursize, to_read, head, tail, fs_index = 1, n_bytes, head_pos, len;
+  svm_fifo_chunk_t *c;
 
   f_load_head_tail_cons (f, &head, &tail);
 
@@ -1148,37 +1150,26 @@ svm_fifo_segments (svm_fifo_t * f, svm_fifo_seg_t * fs)
   if (PREDICT_FALSE (cursize == 0))
     return SVM_FIFO_EEMPTY;
 
-  head_idx = head;
+  to_read = clib_min (cursize, max_bytes);
 
-  if (tail < head)
-    {
-      fs[0].len = f->size - head_idx;
-      fs[0].data = f->head_chunk->data + head_idx;
-      fs[1].len = cursize - fs[0].len;
-      fs[1].data = f->head_chunk->data;
-    }
-  else
+  c = f->head_chunk;
+  head_pos = head - c->start_byte;
+  fs[0].data = c->data + head_pos;
+  fs[0].len = c->length - head_pos;
+  n_bytes = fs[0].len;
+  c = c->next;
+
+  while (n_bytes < to_read && fs_index < n_segs)
     {
-      fs[0].len = cursize;
-      fs[0].data = f->head_chunk->data + head_idx;
-      fs[1].len = 0;
-      fs[1].data = 0;
+      len = clib_min (c->length, to_read - n_bytes);
+      fs[fs_index].data = c->data;
+      fs[fs_index].len = len;
+      n_bytes += len;
+      c = c->next;
+      fs_index += 1;
     }
-  return cursize;
-}
-
-void
-svm_fifo_segments_free (svm_fifo_t * f, svm_fifo_seg_t * fs)
-{
-  u32 head;
 
-  /* consumer owned index */
-  head = f->head;
-
-  ASSERT (fs[0].data == f->head_chunk->data + head);
-  head = (head + fs[0].len + fs[1].len);
-  /* store-rel: consumer owned index (paired with load-acq in producer) */
-  clib_atomic_store_rel_n (&f->head, head);
+  return n_bytes;
 }
 
 /**
diff --git a/src/svm/svm_fifo.h b/src/svm/svm_fifo.h
index f7503c8e900..93ef006fd48 100644
--- a/src/svm/svm_fifo.h
+++ b/src/svm/svm_fifo.h
@@ -348,8 +348,22 @@ int svm_fifo_dequeue_drop (svm_fifo_t * f, u32 len);
  * @param f		fifo
  */
 void svm_fifo_dequeue_drop_all (svm_fifo_t * f);
-int svm_fifo_segments (svm_fifo_t * f, svm_fifo_seg_t * fs);
-void svm_fifo_segments_free (svm_fifo_t * f, svm_fifo_seg_t * fs);
+/**
+ * Get pointers to fifo chunks data in @ref svm_fifo_seg_t array
+ *
+ * Populates fifo segment array with pointers to fifo chunk data and lengths.
+ * Because this returns pointers to data, it must be paired with
+ * @ref svm_fifo_dequeue_drop to actually release the fifo chunks after the
+ * data is consumed.
+ *
+ * @param f		fifo
+ * @param fs		array of fifo segments allocated by caller
+ * @param n_segs	number of fifo segments in array
+ * @param max_bytes	max bytes to be mapped to fifo segments
+ * @return 		number of bytes in fifo segments or SVM_FIFO_EEMPTY
+ */
+int svm_fifo_segments (svm_fifo_t * f, svm_fifo_seg_t * fs, u32 n_segs,
+		       u32 max_bytes);
 /**
  * Add io events subscriber to list
  *