2 files changed, 22 insertions, 10 deletions

diff --git a/src/svm/svm_fifo.c b/src/svm/svm_fifo.c
index 2cce2bf50b3..22cb64eb475 100644
--- a/src/svm/svm_fifo.c
+++ b/src/svm/svm_fifo.c
@@ -1136,10 +1136,11 @@ svm_fifo_fill_chunk_list (svm_fifo_t * f)
 }
 
 int
-svm_fifo_segments (svm_fifo_t * f, svm_fifo_seg_t * fs, u32 n_segs,
-		   u32 max_bytes)
+svm_fifo_segments (svm_fifo_t * f, u32 offset, svm_fifo_seg_t * fs,
+		   u32 n_segs, u32 max_bytes)
 {
-  u32 cursize, to_read, head, tail, fs_index = 1, n_bytes, head_pos, len;
+  u32 cursize, to_read, head, tail, fs_index = 1;
+  u32 n_bytes, head_pos, len, start;
   svm_fifo_chunk_t *c;
 
   f_load_head_tail_cons (f, &head, &tail);
@@ -1150,22 +1151,32 @@ svm_fifo_segments (svm_fifo_t * f, svm_fifo_seg_t * fs, u32 n_segs,
   if (PREDICT_FALSE (cursize == 0))
     return SVM_FIFO_EEMPTY;
 
-  to_read = clib_min (cursize, max_bytes);
+  if (offset >= cursize)
+    return SVM_FIFO_EEMPTY;
+
+  to_read = clib_min (cursize - offset, max_bytes);
+  start = head + offset;
+
+  if (!f->head_chunk)
+    f->head_chunk = svm_fifo_find_chunk (f, head);
 
   c = f->head_chunk;
-  head_pos = head - c->start_byte;
+
+  while (!f_chunk_includes_pos (c, start))
+    c = c->next;
+
+  head_pos = start - c->start_byte;
   fs[0].data = c->data + head_pos;
-  fs[0].len = c->length - head_pos;
+  fs[0].len = clib_min (c->length - head_pos, cursize - offset);
   n_bytes = fs[0].len;
-  c = c->next;
 
   while (n_bytes < to_read && fs_index < n_segs)
     {
+      c = c->next;
       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;
     }
 
diff --git a/src/svm/svm_fifo.h b/src/svm/svm_fifo.h
index 93ef006fd48..408d99a3188 100644
--- a/src/svm/svm_fifo.h
+++ b/src/svm/svm_fifo.h
@@ -357,13 +357,14 @@ void svm_fifo_dequeue_drop_all (svm_fifo_t * f);
  * data is consumed.
  *
  * @param f		fifo
+ * @param offset	offset from where to retrieve segments
  * @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);
+int svm_fifo_segments (svm_fifo_t * f, u32 offset, svm_fifo_seg_t * fs,
+		       u32 n_segs, u32 max_bytes);
 /**
  * Add io events subscriber to list
  *