Lorenzo Bianconi wrote:

From: Eelco Chaudron <echaudro@redhat.com>

This change adds support for tail growing and shrinking for XDP multi-buff.

When called on a multi-buffer packet with a grow request, it will work
on the last fragment of the packet. So the maximum grow size is the
last fragments tailroom, i.e. no new buffer will be allocated.
A XDP mb capable driver is expected to set frag_size in xdp_rxq_info data
structure to notify the XDP core the fragment size. frag_size set to 0 is
interpreted by the XDP core as tail growing is not allowed.
Introduce __xdp_rxq_info_reg utility routine to initialize frag_size field.

When shrinking, it will work from the last fragment, all the way down to
the base buffer depending on the shrinking size. It's important to mention
that once you shrink down the fragment(s) are freed, so you can not grow
again to the original size.

Acked-by: Jakub Kicinski <kuba@kernel.org>
Co-developed-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Eelco Chaudron <echaudro@redhat.com>
---
 drivers/net/ethernet/marvell/mvneta.c |  3 +-
 include/net/xdp.h                     | 16 ++++++-
 net/core/filter.c                     | 65 +++++++++++++++++++++++++++
 net/core/xdp.c                        | 12 ++---
 4 files changed, 88 insertions(+), 8 deletions(-)

LGTM

Acked-by: John Fastabend <john.fastabend@gmail.com>