+/** minimum data size of first buffer in a buffer chain */
+#define VLIB_BUFFER_CHAIN_MIN_FIRST_DATA_SIZE (256)
+
+/**
+ * @brief compress buffer chain in a way where the first buffer is at least
+ * VLIB_BUFFER_CHAIN_MIN_FIRST_DATA_SIZE long
+ *
+ * @param[in] vm - vlib_main
+ * @param[in,out] first - first buffer in chain
+ * @param[in,out] discard_vector - vector of buffer indexes which were removed
+ * from the chain
+ */
+always_inline void
+vlib_buffer_chain_compress (vlib_main_t * vm,
+ vlib_buffer_t * first, u32 ** discard_vector)
+{
+ if (first->current_length >= VLIB_BUFFER_CHAIN_MIN_FIRST_DATA_SIZE ||
+ !(first->flags & VLIB_BUFFER_NEXT_PRESENT))
+ {
+ /* this is already big enough or not a chain */
+ return;
+ }
+ /* probe free list to find allocated buffer size to avoid overfill */
+ vlib_buffer_free_list_index_t index;
+ vlib_buffer_free_list_t *free_list =
+ vlib_buffer_get_buffer_free_list (vm, first, &index);
+
+ u32 want_first_size = clib_min (VLIB_BUFFER_CHAIN_MIN_FIRST_DATA_SIZE,
+ free_list->n_data_bytes -
+ first->current_data);
+ do
+ {
+ vlib_buffer_t *second = vlib_get_buffer (vm, first->next_buffer);
+ u32 need = want_first_size - first->current_length;
+ u32 amount_to_copy = clib_min (need, second->current_length);
+ clib_memcpy_fast (((u8 *) vlib_buffer_get_current (first)) +
+ first->current_length,
+ vlib_buffer_get_current (second), amount_to_copy);
+ first->current_length += amount_to_copy;
+ vlib_buffer_advance (second, amount_to_copy);
+ if (first->flags & VLIB_BUFFER_TOTAL_LENGTH_VALID)
+ {
+ first->total_length_not_including_first_buffer -= amount_to_copy;
+ }
+ if (!second->current_length)
+ {
+ vec_add1 (*discard_vector, first->next_buffer);
+ if (second->flags & VLIB_BUFFER_NEXT_PRESENT)
+ {
+ first->next_buffer = second->next_buffer;
+ }
+ else
+ {
+ first->flags &= ~VLIB_BUFFER_NEXT_PRESENT;
+ }
+ second->flags &= ~VLIB_BUFFER_NEXT_PRESENT;
+ }
+ }
+ while ((first->current_length < want_first_size) &&
+ (first->flags & VLIB_BUFFER_NEXT_PRESENT));
+}
+
+/**
+ * @brief linearize buffer chain - the first buffer is filled, if needed,
+ * buffers are allocated and filled, returns free space in last buffer or
+ * negative on failure
+ *
+ * @param[in] vm - vlib_main
+ * @param[in,out] first - first buffer in chain
+ */
+always_inline int
+vlib_buffer_chain_linearize (vlib_main_t * vm, vlib_buffer_t * first)
+{
+ vlib_buffer_t *b = first;
+ vlib_buffer_free_list_t *fl =
+ vlib_buffer_get_free_list (vm, vlib_buffer_get_free_list_index (b));
+ u32 buf_len = fl->n_data_bytes;
+ // free buffer chain starting from the second buffer
+ int free_count = (b->flags & VLIB_BUFFER_NEXT_PRESENT) != 0;
+ u32 chain_to_free = b->next_buffer;
+
+ u32 len = vlib_buffer_length_in_chain (vm, b);
+ u32 free_len = buf_len - b->current_data - b->current_length;
+ int alloc_len = clib_max (len - free_len, 0); //use the free len in the first buffer
+ int n_buffers = (alloc_len + buf_len - 1) / buf_len;
+ u32 new_buffers[n_buffers];
+
+ u32 n_alloc = vlib_buffer_alloc (vm, new_buffers, n_buffers);
+ if (n_alloc != n_buffers)
+ {
+ vlib_buffer_free_no_next (vm, new_buffers, n_alloc);
+ return -1;
+ }
+
+ vlib_buffer_t *s = b;
+ while (s->flags & VLIB_BUFFER_NEXT_PRESENT)
+ {
+ s = vlib_get_buffer (vm, s->next_buffer);
+ int d_free_len = buf_len - b->current_data - b->current_length;
+ ASSERT (d_free_len >= 0);
+ // chain buf and split write
+ u32 copy_len = clib_min (d_free_len, s->current_length);
+ u8 *d = vlib_buffer_put_uninit (b, copy_len);
+ clib_memcpy (d, vlib_buffer_get_current (s), copy_len);
+ int rest = s->current_length - copy_len;
+ if (rest > 0)
+ {
+ //prev buf is full
+ ASSERT (vlib_buffer_get_tail (b) == b->data + buf_len);
+ ASSERT (n_buffers > 0);
+ b = vlib_buffer_chain_buffer (vm, b, new_buffers[--n_buffers]);
+ //make full use of the new buffers
+ b->current_data = 0;
+ d = vlib_buffer_put_uninit (b, rest);
+ clib_memcpy (d, vlib_buffer_get_current (s) + copy_len, rest);
+ }
+ }
+ vlib_buffer_free (vm, &chain_to_free, free_count);
+ b->flags &= ~VLIB_BUFFER_TOTAL_LENGTH_VALID;
+ if (b == first) /* no buffers addeed */
+ b->flags &= ~VLIB_BUFFER_NEXT_PRESENT;
+ ASSERT (len == vlib_buffer_length_in_chain (vm, first));
+ ASSERT (n_buffers == 0);
+ return buf_len - b->current_data - b->current_length;
+}
+