[PATCH v2 00/13] vhost-user,udp: Handle multiple iovec entries per virtqueue element

[Laurent Vivier <lvivier@redhat.com>]

Some virtio-net drivers (notably iPXE) provide descriptors where the
vnet header and the frame payload are in separate buffers, resulting in
two iovec entries per virtqueue element.  Currently, the RX (host to
guest) path assumes a single iovec per element, which triggers:

  ASSERTION FAILED in virtqueue_map_desc (virtio.c:403):
      num_sg < max_num_sg

This series reworks the UDP vhost-user receive path to support multiple
iovec entries per element, fixing the iPXE crash.

This series only addresses the UDP path.  TCP vhost-user will be
updated to use multi-iov elements in a subsequent series.

v2:
- add iov_truncate(), iov_memset()
- remove iov_tail_truncate() and iov_tail_zero_end()
- manage 802.3 minimum frame size

Laurent Vivier (13):
  iov: Add iov_truncate() helper and use it in vu handlers
  vhost-user: Centralise 802.3 frame padding in vu_collect() and
    vu_flush()
  vhost-user: Use ARRAY_SIZE(elem) instead of VIRTQUEUE_MAX_SIZE
  udp_vu: Use iov_tail to manage virtqueue buffers
  udp_vu: Move virtqueue management from udp_vu_sock_recv() to its
    caller
  iov: Add IOV_PUT_HEADER() to write header data back to iov_tail
  udp: Pass iov_tail to udp_update_hdr4()/udp_update_hdr6()
  udp_vu: Use iov_tail in udp_vu_prepare()
  vu_common: Pass iov_tail to vu_set_vnethdr()
  vu_common: Accept explicit iovec counts in vu_set_element()
  vu_common: Accept explicit iovec count per element in vu_init_elem()
  vu_common: Prepare to use multibuffer with guest RX
  vhost-user,udp: Use 2 iovec entries per element

 iov.c          |  69 +++++++++++++++++
 iov.h          |  17 ++++-
 tcp_vu.c       |  73 +++++++++---------
 udp.c          |  72 +++++++++---------
 udp_internal.h |  10 ++-
 udp_vu.c       | 197 +++++++++++++++++++++++++------------------------
 vu_common.c    | 127 +++++++++++++++++++------------
 vu_common.h    |  20 +++--
 8 files changed, 356 insertions(+), 229 deletions(-)

-- 
2.53.0