[dpdk-dev] [PATCH v4 01/12] mbuf: fix mbuf data room size calculation rte_pktmbuf_pool_init

[Olivier Matz <olivier.matz@6wind.com>]

Deduct the mbuf data room size from mempool->elt_size and priv_size,
instead of using an hardcoded value that is not related to the real
buffer size.

To use rte_pktmbuf_pool_init(), the user can either:
- give a NULL parameter to rte_pktmbuf_pool_init(): in this case, the
  private size is assumed to be 0, and the room size is
  mp->elt_size - sizeof(struct rte_mbuf).
- give the rte_pktmbuf_pool_private filled with appropriate
  data_room_size and priv_size values.

Signed-off-by: Olivier Matz <olivier.matz@6wind.com>
---
 app/test-pmd/testpmd.c                 |  1 +
 doc/guides/rel_notes/updating_apps.rst | 12 ++++++++++++
 examples/vhost/main.c                  |  5 ++---
 lib/librte_mbuf/rte_mbuf.c             | 27 ++++++++++++++++++++-------
 lib/librte_mbuf/rte_mbuf.h             |  3 ++-
 5 files changed, 37 insertions(+), 11 deletions(-)

diff --git a/app/test-pmd/testpmd.c b/app/test-pmd/testpmd.c
index 3057791..10e4347 100644
--- a/app/test-pmd/testpmd.c
+++ b/app/test-pmd/testpmd.c
@@ -443,6 +443,7 @@ testpmd_mbuf_pool_ctor(struct rte_mempool *mp,
 	mbp_ctor_arg = (struct mbuf_pool_ctor_arg *) opaque_arg;
 	mbp_priv = rte_mempool_get_priv(mp);
 	mbp_priv->mbuf_data_room_size = mbp_ctor_arg->seg_buf_size;
+	mbp_priv->mbuf_priv_size = 0;
 }
 
 static void
diff --git a/doc/guides/rel_notes/updating_apps.rst b/doc/guides/rel_notes/updating_apps.rst
index 4dbf268..f513615 100644
--- a/doc/guides/rel_notes/updating_apps.rst
+++ b/doc/guides/rel_notes/updating_apps.rst
@@ -4,6 +4,18 @@ Updating Applications from Previous Versions
 Although backward compatibility is being maintained across DPDK releases, code written for previous versions of the DPDK
 may require some code updates to benefit from performance and user experience enhancements provided in later DPDK releases.
 
+DPDK 2.0 to DPDK 2.1
+--------------------
+
+*   The second argument of rte_pktmbuf_pool_init(mempool, opaque) is now a
+    pointer to a struct rte_pktmbuf_pool_private instead of a uint16_t
+    casted into a pointer. Backward compatibility is preserved when the
+    argument was NULL which is the majority of use cases, but not if the
+    opaque pointer was not NULL, as it is not technically feasible. In
+    this case, the application has to be modified to properly fill a
+    rte_pktmbuf_pool_private structure and pass it to
+    rte_pktmbuf_pool_init().
+
 DPDK 1.7 to DPDK 1.8
 --------------------
 
diff --git a/examples/vhost/main.c b/examples/vhost/main.c
index ad10f82..fc73d1e 100644
--- a/examples/vhost/main.c
+++ b/examples/vhost/main.c
@@ -2844,11 +2844,10 @@ static void
 setup_mempool_tbl(int socket, uint32_t index, char *pool_name,
 	char *ring_name, uint32_t nb_mbuf)
 {
-	uint16_t roomsize = VIRTIO_DESCRIPTOR_LEN_ZCP + RTE_PKTMBUF_HEADROOM;
 	vpool_array[index].pool
 		= rte_mempool_create(pool_name, nb_mbuf, MBUF_SIZE_ZCP,
 		MBUF_CACHE_SIZE_ZCP, sizeof(struct rte_pktmbuf_pool_private),
-		rte_pktmbuf_pool_init, (void *)(uintptr_t)roomsize,
+		rte_pktmbuf_pool_init, NULL,
 		rte_pktmbuf_init, NULL, socket, 0);
 	if (vpool_array[index].pool != NULL) {
 		vpool_array[index].ring
@@ -2870,7 +2869,7 @@ setup_mempool_tbl(int socket, uint32_t index, char *pool_name,
 		}
 
 		/* Need consider head room. */
-		vpool_array[index].buf_size = roomsize - RTE_PKTMBUF_HEADROOM;
+		vpool_array[index].buf_size = VIRTIO_DESCRIPTOR_LEN_ZCP;
 	} else {
 		rte_exit(EXIT_FAILURE, "mempool_create(%s) failed", pool_name);
 	}
diff --git a/lib/librte_mbuf/rte_mbuf.c b/lib/librte_mbuf/rte_mbuf.c
index 526b18d..231cfb8 100644
--- a/lib/librte_mbuf/rte_mbuf.c
+++ b/lib/librte_mbuf/rte_mbuf.c
@@ -81,17 +81,30 @@ rte_ctrlmbuf_init(struct rte_mempool *mp,
 void
 rte_pktmbuf_pool_init(struct rte_mempool *mp, void *opaque_arg)
 {
-	struct rte_pktmbuf_pool_private *mbp_priv;
+	struct rte_pktmbuf_pool_private *user_mbp_priv, *mbp_priv;
+	struct rte_pktmbuf_pool_private default_mbp_priv;
 	uint16_t roomsz;
 
-	mbp_priv = rte_mempool_get_priv(mp);
-	roomsz = (uint16_t)(uintptr_t)opaque_arg;
+	RTE_MBUF_ASSERT(mp->elt_size >= sizeof(struct rte_mbuf));
 
-	/* Use default data room size. */
-	if (0 == roomsz)
-		roomsz = 2048 + RTE_PKTMBUF_HEADROOM;
+	/* if no structure is provided, assume no mbuf private area */
+	user_mbp_priv = opaque_arg;
+	if (user_mbp_priv == NULL) {
+		default_mbp_priv.mbuf_priv_size = 0;
+		if (mp->elt_size > sizeof(struct rte_mbuf))
+			roomsz = mp->elt_size - sizeof(struct rte_mbuf);
+		else
+			roomsz = 0;
+		default_mbp_priv.mbuf_data_room_size = roomsz;
+		user_mbp_priv = &default_mbp_priv;
+	}
 
-	mbp_priv->mbuf_data_room_size = roomsz;
+	RTE_MBUF_ASSERT(mp->elt_size >= sizeof(struct rte_mbuf) +
+		user_mbp_priv->mbuf_data_room_size +
+		user_mbp_priv->mbuf_priv_size);
+
+	mbp_priv = rte_mempool_get_priv(mp);
+	memcpy(mbp_priv, user_mbp_priv, sizeof(*mbp_priv));
 }
 
 /*
diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
index 45f73c2..13fd626 100644
--- a/lib/librte_mbuf/rte_mbuf.h
+++ b/lib/librte_mbuf/rte_mbuf.h
@@ -348,7 +348,8 @@ struct rte_mbuf {
  * appended after the mempool structure (in private data).
  */
 struct rte_pktmbuf_pool_private {
-	uint16_t mbuf_data_room_size; /**< Size of data space in each mbuf.*/
+	uint16_t mbuf_data_room_size; /**< Size of data space in each mbuf. */
+	uint16_t mbuf_priv_size;      /**< Size of private area in each mbuf. */
 };
 
 #ifdef RTE_LIBRTE_MBUF_DEBUG
-- 
2.1.4