[dpdk-dev] [PATCH 0/5] virtio/mbuf: fix virtio tso with shared mbufs

Olivier Matz olivier.matz at 6wind.com
Thu Nov 24 09:56:33 CET 2016

This patchset fixes the transmission of cloned mbufs when using
virtio + TSO. The problem is we need to fix the L4 checksum in the
packet, but it should be considered as read-only, as pointed-out
by Stephen here:

Unfortunatly the patchset is quite big, but I did not manage to
find a shorter solution. The first patches add some mbuf helpers
that are used in virtio in the last patch.

This last patch adds a zone for each tx ring entry where headers
can be copied, patched, and referenced by virtio descriptors in
case the mbuf is read-only. If its not the case, the mbuf is
modified as before.

I tested with the same test plan than the one described in
(only the TSO test case).

I also replayed the test with the following patches to validate
the code path for:

- segmented packets (it forces a local copy in virtio_tso_fix_cksum)

--- a/lib/librte_mbuf/rte_mbuf.c
+++ b/lib/librte_mbuf/rte_mbuf.c
@@ -279,7 +279,7 @@ void *__rte_pktmbuf_read(const struct rte_mbuf *m, uint32_t off,
                seg = seg->next;
-       if (off + len <= rte_pktmbuf_data_len(seg))
+       if (0 && off + len <= rte_pktmbuf_data_len(seg))
                return rte_pktmbuf_mtod_offset(seg, char *, off);
        /* rare case: header is split among several segments */
diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
index 9dc6f10..5a4312a 100644
--- a/lib/librte_mbuf/rte_mbuf.h
+++ b/lib/librte_mbuf/rte_mbuf.h
@@ -1671,7 +1671,7 @@ void *__rte_pktmbuf_read(const struct rte_mbuf *m, uint32_t off,
 static inline void *rte_pktmbuf_read(const struct rte_mbuf *m,
        uint32_t off, uint32_t len, void *buf)
-       if (likely(off + len <= rte_pktmbuf_data_len(m)))
+       if (likely(0 && off + len <= rte_pktmbuf_data_len(m)))
                return rte_pktmbuf_mtod_offset(m, char *, off);
                return __rte_pktmbuf_read(m, off, len, buf);

- and for shared mbuf (force to use the buffer in virtio tx ring)

--- a/drivers/net/virtio/virtio_rxtx.c
+++ b/drivers/net/virtio/virtio_rxtx.c
@@ -225,7 +225,7 @@ virtio_tso_fix_cksum(struct rte_mbuf *m, char *hdr, size_t hdr_sz)
        int shared = 0;
        /* mbuf is write-only, we need to copy the headers in a linear buffer */
-       if (unlikely(rte_pktmbuf_data_is_shared(m, 0, hdrlen))) {
+       if (unlikely(1 || rte_pktmbuf_data_is_shared(m, 0, hdrlen))) {
                shared = 1;
                /* network headers are too big, there's nothing we can do */

Olivier Matz (5):
  mbuf: remove const attribute in mbuf read function
  mbuf: new helper to check if a mbuf is shared
  mbuf: new helper to write data in a mbuf chain
  mbuf: new helper to copy data from a mbuf
  net/virtio: fix Tso when mbuf is shared

 app/test/test_mbuf.c                 |  62 +++++++++++++-
 drivers/net/virtio/virtio_rxtx.c     | 119 ++++++++++++++++++--------
 drivers/net/virtio/virtqueue.h       |   2 +
 lib/librte_mbuf/rte_mbuf.c           |  46 +++++++++-
 lib/librte_mbuf/rte_mbuf.h           | 157 ++++++++++++++++++++++++++++++++++-
 lib/librte_mbuf/rte_mbuf_version.map |   6 ++
 6 files changed, 347 insertions(+), 45 deletions(-)


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