Re: [PATCH v9 3/3] udp: Pass iov_tail to udp_update_hdr4()/udp_update_hdr6()

[David Gibson <david@gibson.dropbear.id.au>]

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On Tue, May 19, 2026 at 10:03:39AM +0200, Laurent Vivier wrote:
> On 5/19/26 07:08, David Gibson wrote:
> > On Mon, May 18, 2026 at 02:26:25PM +0200, Laurent Vivier wrote:
> > > Change udp_update_hdr4() and udp_update_hdr6() to take an iov_tail
> > > pointing at the UDP frame instead of a contiguous udp_payload_t buffer
> > > and explicit data length.  This lets vhost-user pass scatter-gather
> > > virtqueue buffers directly without an intermediate copy.
> > > 
> > > The UDP header is built into a local struct udphdr and written back with
> > > IOV_PUSH_HEADER().  On the tap side, udp_tap_prepare() wraps the
> > > existing udp_payload_t in a two-element iov to match the new interface.
> > > 
> > > Signed-off-by: Laurent Vivier <lvivier@redhat.com>
> > 
> > Alas, this still has a potentially aliased memcpy(), see below.
> 
> Did you see I updated patch 2 to avoid the memcpy() if the header is
> already in place?
> (I think I should have removed your R-b...)

I saw the note in the changelog, but I didn't spot the place in the
code specifically - I think I skipped patch 2 because of the R-b and
assumed the change was in patch 3.  Unfortunately the one in this
patch is still there.

-- 
David Gibson (he or they)	| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you, not the other way
				| around.
http://www.ozlabs.org/~dgibson

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