Re: [PATCH v4 00/10] vhost-user: Preparatory series for multiple iovec entries per virtqueue element

[Stefano Brivio <sbrivio@redhat.com>]

On Wed, 13 May 2026 13:52:08 +0200
Laurent Vivier <lvivier@redhat.com> wrote:

> Currently, the vhost-user path assumes each virtqueue element contains
> exactly one iovec entry covering the entire frame.  This assumption
> breaks as 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.
> 
> This series refactors the vhost-user data path so that frame lengths,
> header sizes, and padding are tracked and passed explicitly rather than
> being derived from iovec sizes.  This decoupling is a prerequisite for
> correctly handling padding of multi-buffer frames.
> 
> The changes in this series can be split in 3 groups:
> 
> - New iov helpers (patches 1-2):
> 
>    iov_memset() and iov_memcpy() operate across iovec boundaries.
>    These are needed by the final patch to pad and copy frame data
>    when a frame spans multiple iovec entries.
> 
> - Structural refactoring (patches 3-5):
> 
>    Move vnethdr setup into vu_flush(), separate virtqueue management
>    from socket I/O in the UDP path, and pass iov arrays explicitly
>    instead of using file-scoped state.  These changes make it possible
>    to pass explicit frame lengths through the stack, which is required
>    to pad frames independently of iovec layout.
> 
> - Explicit length passing throughout the stack (patches 6-10):
> 
>    Thread explicit L4, L2, frame, and data lengths through checksum,
>    pcap, vu_flush(), and tcp_fill_headers(), replacing lengths that
>    were previously derived from iovec sizes.  With lengths tracked
>    explicitly, the final patch can centralise Ethernet frame padding
>    into vu_collect() and a new vu_pad() helper that correctly pads
>    frames spanning multiple iovec entries.
> 
> v4:
> - rebase
> - iov_memcpy: use size_t for loop indices i and j
> - udp_vu: reorder elem[] declaration for inverted christmas tree style
> - pcap: wrap pcap_iov() declaration and definition to respect line length
> - write_remainder(): update length parameter description
> - Add Reviewed-by tags from Jon and David

Applied, sorry for the delay.

-- 
Stefano