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Subject: Re: [virtio-comment] Re: [PATCH v4 1/2] virtio-net: update description for VIRTIO_NET_F_GUEST_CSUM.



å 2023/12/4 äå3:18, Jason Wang åé:

On Fri, Dec 1, 2023 at 3:16âPM Heng Qi <hengqi@linux.alibaba.com> wrote:



å 2023/12/1 äå3:05, Jason Wang åé:

On Fri, Dec 1, 2023 at 2:30âPM Heng Qi <hengqi@linux.alibaba.com> wrote:


å 2023/12/1 äå2:24, Heng Qi åé:

å 2023/12/1 äå1:18, Jason Wang åé:

On Wed, Nov 29, 2023 at 4:23âPM Heng Qi <hengqi@linux.alibaba.com>
wrote:

å 2023/11/29 äå4:00, Jason Wang åé:

On Tue, Nov 28, 2023 at 4:08âPM Heng Qi <hengqi@linux.alibaba.com>
wrote:

To prevent readers from misunderstanding that the driver can
only handles packets with partial checksum when
VIRTIO_NET_F_GUEST_CSUM is negotiated, we update the description.

Signed-off-by: Heng Qi <hengqi@linux.alibaba.com>
---
     device-types/net/description.tex | 2 +-
     1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/device-types/net/description.tex
b/device-types/net/description.tex
index aff5e08..529f470 100644
--- a/device-types/net/description.tex
+++ b/device-types/net/description.tex
@@ -38,7 +38,7 @@ \subsection{Feature bits}\label{sec:Device Types
/ Network Device / Feature bits
     \begin{description}
     \item[VIRTIO_NET_F_CSUM (0)] Device handles packets with
partial checksum offload.

-\item[VIRTIO_NET_F_GUEST_CSUM (1)] Driver handles packets with
partial checksum.
+\item[VIRTIO_NET_F_GUEST_CSUM (1)] Driver handles packets with
partial checksum or full checksum.

So patch 2 said

"
+\item[VIRTIO_NET_F_GUEST_FULL_CSUM (64)] Driver handles packets with
full checksum.
     \end{description}
"

Is there any difference between the two "full checksum" here?

There's no difference.

The core is that VIRTIO_NET_F_GUEST_FULL_CSUM means that the driver
"can
only" handle packets with full checksum.

This seems to be odd.

Driver can always handle packet with full checksum, no?

Yes.


I meant it
will be then to be functional equivalent to !
VIRTIO_NET_F_GUEST_FULL_CSUM?

Are you referring to
"functional equivalent to !VIRTIO_NET_F_GUEST_CSUM" ?

Sorry, this is a typo. I meant

Are you referring to
"functional equivalent to !VIRTIO_NET_F_GUEST_FULL_CSUM" ?


If so, I think it's no.

Maybe a description similar to the following would be more clearer:

+\item[VIRTIO_NET_F_GUEST_FULL_CSUM (64)] Driver does not handle
packets with partial checksum.

I may miss something here, but what's the difference between

VIRTIO_NET_F_GUEST_FULL_CSUM

and

!VIRTIO_NET_F_GUEST_CSUM?

  From the device perspective:

If !VIRTIO_NET_F_GUEST_CSUM, the device delivers packets with full
checksum to the driver,
but the device can not validate the checksum for these packets. That is,
the flags in virtio-net-hdr
will not contain _DATA_VALID, and the driver or stack needs to validate
these packets.

If VIRTIO_NET_F_GUEST_FULL_CSUM, the device delivers packets with full
checksum to the driver,
and the device can validate the checksum for these packets. That is, the
flags in virtio-net-hdr
will contain _DATA_VALID,

I think DATA_VALID is optional here as device can't recognize all type
of protocols.
Yes, you are right, so I used "device *can*" here. Which packet types the device recognizes or validates depends on the device's implementation. This is also the current practice of GUEST_CSUM. 




and the driver or stack does not need to
validate these packets.

Ok, so I think there're something that is subtle here,


Ok, I see.


and that's why
I'm asking here:

1) "Driver does not handle packets with partial checksum" is not
accurate, !GUEST_CUSM also fit for this definition.
2) "Driver handles packets with full checksum" is kind of ambiguous as
it doesn't say whether or not the packet has been validated or not.


Maybe the description below would be less subtle?
+\item[VIRTIO_NET_F_GUEST_CSUM (1)] Driver handles packets with partial checksum or full checksum. +\item[VIRTIO_NET_F_GUEST_FULL_CSUM (64)] The driver handles packets with full checksum, 
and the device optionally validates the packet's checksum.

Thanks!



Thanks


Thanks!


Thanks


Thanks!


Thanks


Thanks!


Thanks


\item[VIRTIO_NET_F_CTRL_GUEST_OFFLOADS (2)] Control channel offloads
             reconfiguration support.
--
2.19.1.6.gb485710b


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