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. 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 (5): vhost-user: Centralise Ethernet frame padding in vu_collect(), vu_pad() and vu_flush() 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() and with_header() to write header data back to iov_tail udp: Pass iov_tail to udp_update_hdr4()/udp_update_hdr6() iov.c | 47 +++++++++++ iov.h | 27 ++++++- tcp_vu.c | 22 ++---- udp.c | 129 ++++++++++++++++-------------- udp_internal.h | 6 +- udp_vu.c | 210 ++++++++++++++++++++++++------------------------- vu_common.c | 76 ++++++++++++------ vu_common.h | 2 +- 8 files changed, 310 insertions(+), 209 deletions(-) -- 2.53.0