Re: [PATCH net-next 2/6] netdevsim: psp: remove unnecessary UDP checksum computation

[Daniel Zahka]

On 5/11/26 1:01 PM, Willem de Bruijn wrote:
> Daniel Zahka wrote:
> > The PSP spec requires the implementations accept 0 checksum in psp-udp
> > header. Let's take advantage of that to trim netdevsim's psp code
> > down. psp_dev_encapsulate() already sets uh->check to 0.
> >
> > Assisted-by: Claude:claude-opus-4.6
> > Signed-off-by: Daniel Zahka <daniel.zahka@xxxxxxxxx>
> > ---
> >   drivers/net/netdevsim/psp.c | 32 --------------------------------
> >   1 file changed, 32 deletions(-)
> >
> > diff --git a/drivers/net/netdevsim/psp.c b/drivers/net/netdevsim/psp.c
> > index 5073bda60883..75740e2a731f 100644
> > --- a/drivers/net/netdevsim/psp.c
> > +++ b/drivers/net/netdevsim/psp.c
> > @@ -1,8 +1,6 @@
> >   // SPDX-License-Identifier: GPL-2.0
> >   
> > -#include <linux/ip.h>
> >   #include <linux/skbuff.h>
> > -#include <net/ip6_checksum.h>
> >   #include <net/psp.h>
> >   #include <net/sock.h>
> >   
> > @@ -81,36 +79,6 @@ nsim_do_psp(struct sk_buff *skb, struct netdevsim *ns,
> >   			      skb->len - skb_inner_transport_offset(skb));
> >   		u64_stats_update_end(&ns->psp.syncp);
> >   	} else {
> > -		struct ipv6hdr *ip6h __maybe_unused;
> > -		struct iphdr *iph;
> > -		struct udphdr *uh;
> > -		__wsum csum;
> > -
> > -		/* Do not decapsulate. Receive the skb with the udp and psp
> > -		 * headers still there as if this is a normal udp packet.
> > -		 * psp_dev_encapsulate() sets udp checksum to 0, so we need to
> > -		 * provide a valid checksum here, so the skb isn't dropped.
> > -		 */
> Perhaps this was here as IPv6 does not allow zero checksums except for
> tunneling in specific cases (RFC 6936)?


Yes it was originally here for IPv6. It was needed to make a test case 
pass that ultimately never got upstreamed (yet). The test basically used 
the psp_dev_ops::set_config() function to turn psp rx off midflow, and 
then tried to catch packets with a udp socket listening on port 1000. At 
the time I didn't realize that I could probably make the test work by 
opting the socket into a setting for RFC 6936 with setsockopt().


> It seems benign enough to keep the code. Do you have a specific reason
> to remove it, beyond reducing LoC?


It was just to reduce LoC for the series :) I can put it back in if you 
like, though as I mentioned, none of the current tests cover that the 
psp-udp csum is correct.