[PATCH v5 0/8] 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.

v5:
- This version doesn't change the padding system regarding v4,
  it's a complex task that will be addressed in another version
- reorder patches and add new patches
- remove IOV_PUT_HEADER()/with_header() and introduce IOV_PUSH_HEADER()
- don't use the iov_tail to provide the headers to the functions
- move vu_set_vnethdr() to vu_flush(), extract vu_queue_notify()
- move vu_flush() inside loop in tcp_vu_data_from_sock() to flush data
  by frame and not by full data length

v4:
- rebase
- replace ASSERT() by assert()

v3:
- include the series "Decouple iovec management from virtqueues elements"
- because of this series, drop:
  "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"
- drop "vu_common: Pass iov_tail to vu_set_vnethdr()"
  as the specs insures a buffer is big enough to contain vnet header
- introduce "with_header()" and merge
  "udp: Pass iov_tail to udp_update_hdr4()/udp_update_hdr6()" and
  "udp_vu: Use iov_tail in udp_vu_prepare()"
  to use it

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

Laurent Vivier (8):
  iov: Introduce iov_memset()
  vu_common: Move vnethdr setup into vu_flush()
  vhost-user: Centralise Ethernet frame padding in vu_collect(),
    vu_pad() and vu_flush()
  udp_vu: Move virtqueue management from udp_vu_sock_recv() to its
    caller
  udp_vu: Pass iov explicitly to helpers instead of using file-scoped
    array
  udp_vu: Allow virtqueue elements with multiple iovec entries
  iov: Introduce IOV_PUSH_HEADER() macro
  udp: Pass iov_tail to udp_update_hdr4()/udp_update_hdr6()

 iov.c          |  48 ++++++++++++
 iov.h          |  13 ++++
 tcp_vu.c       |  36 +++------
 udp.c          |  81 ++++++++++----------
 udp_internal.h |  10 +--
 udp_vu.c       | 201 +++++++++++++++++++++++++------------------------
 vu_common.c    |  64 ++++++++++------
 vu_common.h    |   3 +-
 8 files changed, 263 insertions(+), 193 deletions(-)

-- 
2.53.0