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Michael S. Tsirkin

2018-Apr-11 22:49 UTC

[PATCH net-next 1/5] virtio: Add support for SCTP checksum offloading

On Mon, Apr 02, 2018 at 09:40:02AM -0400, Vladislav Yasevich
wrote:> To support SCTP checksum offloading, we need to add a new feature
> to virtio_net, so we can negotiate support between the hypervisor
> and the guest.
> 
> The signalling to the guest that an alternate checksum needs to
> be used is done via a new flag in the virtio_net_hdr.  If the
> flag is set, the host will know to perform an alternate checksum
> calculation, which right now is only CRC32c.
> 
> Signed-off-by: Vladislav Yasevich <vyasevic at redhat.com>
> ---
>  drivers/net/virtio_net.c        | 11 ++++++++---
>  include/linux/virtio_net.h      |  6 ++++++
>  include/uapi/linux/virtio_net.h |  2 ++
>  3 files changed, 16 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 7b187ec..b601294 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -2724,9 +2724,14 @@ static int virtnet_probe(struct virtio_device *vdev)
>  	/* Do we support "hardware" checksums? */
>  	if (virtio_has_feature(vdev, VIRTIO_NET_F_CSUM)) {
>  		/* This opens up the world of extra features. */
> -		dev->hw_features |= NETIF_F_HW_CSUM | NETIF_F_SG;
> +		netdev_features_t sctp = 0;
> +
> +		if (virtio_has_feature(vdev, VIRTIO_NET_F_SCTP_CSUM))
> +			sctp |= NETIF_F_SCTP_CRC;
> +
> +		dev->hw_features |= NETIF_F_HW_CSUM | NETIF_F_SG | sctp;
>  		if (csum)
> -			dev->features |= NETIF_F_HW_CSUM | NETIF_F_SG;
> +			dev->features |= NETIF_F_HW_CSUM | NETIF_F_SG | sctp;
>  
>  		if (virtio_has_feature(vdev, VIRTIO_NET_F_GSO)) {
>  			dev->hw_features |= NETIF_F_TSO
> @@ -2952,7 +2957,7 @@ static struct virtio_device_id id_table[] = {
>  };
>  
>  #define VIRTNET_FEATURES \
> -	VIRTIO_NET_F_CSUM, VIRTIO_NET_F_GUEST_CSUM, \
> +	VIRTIO_NET_F_CSUM, VIRTIO_NET_F_GUEST_CSUM,  VIRTIO_NET_F_SCTP_CSUM, \
>  	VIRTIO_NET_F_MAC, \
>  	VIRTIO_NET_F_HOST_TSO4, VIRTIO_NET_F_HOST_UFO, VIRTIO_NET_F_HOST_TSO6, \
>  	VIRTIO_NET_F_HOST_ECN, VIRTIO_NET_F_GUEST_TSO4, VIRTIO_NET_F_GUEST_TSO6,
\
> diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h
> index f144216..2e7a64a 100644
> --- a/include/linux/virtio_net.h
> +++ b/include/linux/virtio_net.h
> @@ -39,6 +39,9 @@ static inline int virtio_net_hdr_to_skb(struct sk_buff
*skb,
>  
>  		if (!skb_partial_csum_set(skb, start, off))
>  			return -EINVAL;
> +
> +		if (hdr->flags & VIRTIO_NET_HDR_F_CSUM_NOT_INET)
> +			skb->csum_not_inet = 1;
>  	}
>  
>  	if (hdr->gso_type != VIRTIO_NET_HDR_GSO_NONE) {
> @@ -96,6 +99,9 @@ static inline int virtio_net_hdr_from_skb(const struct
sk_buff *skb,
>  		hdr->flags = VIRTIO_NET_HDR_F_DATA_VALID;
>  	} /* else everything is zero */
>  
> +	if (skb->csum_not_inet)
> +		hdr->flags &= VIRTIO_NET_HDR_F_CSUM_NOT_INET;
> +
>  	return 0;
>  }
>  
> diff --git a/include/uapi/linux/virtio_net.h
b/include/uapi/linux/virtio_net.h
> index 5de6ed3..3f279c8 100644
> --- a/include/uapi/linux/virtio_net.h
> +++ b/include/uapi/linux/virtio_net.h
> @@ -36,6 +36,7 @@
>  #define VIRTIO_NET_F_GUEST_CSUM	1	/* Guest handles pkts w/ partial csum */
>  #define VIRTIO_NET_F_CTRL_GUEST_OFFLOADS 2 /* Dynamic offload
configuration. */
>  #define VIRTIO_NET_F_MTU	3	/* Initial MTU advice */
> +#define VIRTIO_NET_F_SCTP_CSUM  4	/* SCTP checksum offload support */
>  #define VIRTIO_NET_F_MAC	5	/* Host has given MAC address. */
>  #define VIRTIO_NET_F_GUEST_TSO4	7	/* Guest can handle TSOv4 in. */
>  #define VIRTIO_NET_F_GUEST_TSO6	8	/* Guest can handle TSOv6 in. */
Is this a guest or a host checksum? We should differenciate between the
two.

> @@ -101,6 +102,7 @@ struct virtio_net_config {
>  struct virtio_net_hdr_v1 {
>  #define VIRTIO_NET_HDR_F_NEEDS_CSUM	1	/* Use csum_start, csum_offset */
>  #define VIRTIO_NET_HDR_F_DATA_VALID	2	/* Csum is valid */
> +#define VIRTIO_NET_HDR_F_CSUM_NOT_INET  4       /* Checksum is not inet */
>  	__u8 flags;
>  #define VIRTIO_NET_HDR_GSO_NONE		0	/* Not a GSO frame */
>  #define VIRTIO_NET_HDR_GSO_TCPV4	1	/* GSO frame, IPv4 TCP (TSO) */
> -- 
> 2.9.5

Vlad Yasevich

2018-Apr-16 13:45 UTC

head link

[PATCH net-next 1/5] virtio: Add support for SCTP checksum offloading

On 04/11/2018 06:49 PM, Michael S. Tsirkin wrote:> On Mon, Apr 02, 2018 at 09:40:02AM -0400, Vladislav Yasevich wrote:
>> To support SCTP checksum offloading, we need to add a new feature
>> to virtio_net, so we can negotiate support between the hypervisor
>> and the guest.
>>
>> The signalling to the guest that an alternate checksum needs to
>> be used is done via a new flag in the virtio_net_hdr.  If the
>> flag is set, the host will know to perform an alternate checksum
>> calculation, which right now is only CRC32c.
>>
>> Signed-off-by: Vladislav Yasevich <vyasevic at redhat.com>
>> ---
>>  drivers/net/virtio_net.c        | 11 ++++++++---
>>  include/linux/virtio_net.h      |  6 ++++++
>>  include/uapi/linux/virtio_net.h |  2 ++
>>  3 files changed, 16 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>> index 7b187ec..b601294 100644
>> --- a/drivers/net/virtio_net.c
>> +++ b/drivers/net/virtio_net.c
>> @@ -2724,9 +2724,14 @@ static int virtnet_probe(struct virtio_device
*vdev)
>>  	/* Do we support "hardware" checksums? */
>>  	if (virtio_has_feature(vdev, VIRTIO_NET_F_CSUM)) {
>>  		/* This opens up the world of extra features. */
>> -		dev->hw_features |= NETIF_F_HW_CSUM | NETIF_F_SG;
>> +		netdev_features_t sctp = 0;
>> +
>> +		if (virtio_has_feature(vdev, VIRTIO_NET_F_SCTP_CSUM))
>> +			sctp |= NETIF_F_SCTP_CRC;
>> +
>> +		dev->hw_features |= NETIF_F_HW_CSUM | NETIF_F_SG | sctp;
>>  		if (csum)
>> -			dev->features |= NETIF_F_HW_CSUM | NETIF_F_SG;
>> +			dev->features |= NETIF_F_HW_CSUM | NETIF_F_SG | sctp;
>>  
>>  		if (virtio_has_feature(vdev, VIRTIO_NET_F_GSO)) {
>>  			dev->hw_features |= NETIF_F_TSO
>> @@ -2952,7 +2957,7 @@ static struct virtio_device_id id_table[] = {
>>  };
>>  
>>  #define VIRTNET_FEATURES \
>> -	VIRTIO_NET_F_CSUM, VIRTIO_NET_F_GUEST_CSUM, \
>> +	VIRTIO_NET_F_CSUM, VIRTIO_NET_F_GUEST_CSUM,  VIRTIO_NET_F_SCTP_CSUM,
\
>>  	VIRTIO_NET_F_MAC, \
>>  	VIRTIO_NET_F_HOST_TSO4, VIRTIO_NET_F_HOST_UFO,
VIRTIO_NET_F_HOST_TSO6, \
>>  	VIRTIO_NET_F_HOST_ECN, VIRTIO_NET_F_GUEST_TSO4,
VIRTIO_NET_F_GUEST_TSO6, \
>> diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h
>> index f144216..2e7a64a 100644
>> --- a/include/linux/virtio_net.h
>> +++ b/include/linux/virtio_net.h
>> @@ -39,6 +39,9 @@ static inline int virtio_net_hdr_to_skb(struct
sk_buff *skb,
>>  
>>  		if (!skb_partial_csum_set(skb, start, off))
>>  			return -EINVAL;
>> +
>> +		if (hdr->flags & VIRTIO_NET_HDR_F_CSUM_NOT_INET)
>> +			skb->csum_not_inet = 1;
>>  	}
>>  
>>  	if (hdr->gso_type != VIRTIO_NET_HDR_GSO_NONE) {
>> @@ -96,6 +99,9 @@ static inline int virtio_net_hdr_from_skb(const
struct sk_buff *skb,
>>  		hdr->flags = VIRTIO_NET_HDR_F_DATA_VALID;
>>  	} /* else everything is zero */
>>  
>> +	if (skb->csum_not_inet)
>> +		hdr->flags &= VIRTIO_NET_HDR_F_CSUM_NOT_INET;
>> +
>>  	return 0;
>>  }
>>  
>> diff --git a/include/uapi/linux/virtio_net.h
b/include/uapi/linux/virtio_net.h
>> index 5de6ed3..3f279c8 100644
>> --- a/include/uapi/linux/virtio_net.h
>> +++ b/include/uapi/linux/virtio_net.h
>> @@ -36,6 +36,7 @@
>>  #define VIRTIO_NET_F_GUEST_CSUM	1	/* Guest handles pkts w/ partial
csum */
>>  #define VIRTIO_NET_F_CTRL_GUEST_OFFLOADS 2 /* Dynamic offload
configuration. */
>>  #define VIRTIO_NET_F_MTU	3	/* Initial MTU advice */
>> +#define VIRTIO_NET_F_SCTP_CSUM  4	/* SCTP checksum offload support */
>>  #define VIRTIO_NET_F_MAC	5	/* Host has given MAC address. */
>>  #define VIRTIO_NET_F_GUEST_TSO4	7	/* Guest can handle TSOv4 in. */
>>  #define VIRTIO_NET_F_GUEST_TSO6	8	/* Guest can handle TSOv6 in. */
> 
> Is this a guest or a host checksum? We should differenciate between the
> two.
I suppose this is HOST checksum, since it behaves like VIRTIO_NET_F_CSUM only
for
SCTP.  I couldn't find the use for the GUEST side flag, since there
technically
isn't any validations and there is no additional mappings from VIRTIO flag
to a
NETIF flag.

If the feature is negotiated, the guest ends up generating partially
check-summed
packets, and the host turns on appropriate flags on it's side.   The host
will
also make sure the checksum if fixed up if the guest doesn't support it.
So 1 flag is currently all that is needed.

-vlad
> 
> 
>> @@ -101,6 +102,7 @@ struct virtio_net_config {
>>  struct virtio_net_hdr_v1 {
>>  #define VIRTIO_NET_HDR_F_NEEDS_CSUM	1	/* Use csum_start, csum_offset
*/
>>  #define VIRTIO_NET_HDR_F_DATA_VALID	2	/* Csum is valid */
>> +#define VIRTIO_NET_HDR_F_CSUM_NOT_INET  4       /* Checksum is not
inet */
>>  	__u8 flags;
>>  #define VIRTIO_NET_HDR_GSO_NONE		0	/* Not a GSO frame */
>>  #define VIRTIO_NET_HDR_GSO_TCPV4	1	/* GSO frame, IPv4 TCP (TSO) */
>> -- 
>> 2.9.5

Michael S. Tsirkin

2018-Apr-16 15:52 UTC

head link

[PATCH net-next 1/5] virtio: Add support for SCTP checksum offloading

On Mon, Apr 16, 2018 at 09:45:48AM -0400, Vlad Yasevich
wrote:> On 04/11/2018 06:49 PM, Michael S. Tsirkin wrote:
> > On Mon, Apr 02, 2018 at 09:40:02AM -0400, Vladislav Yasevich wrote:
> >> To support SCTP checksum offloading, we need to add a new feature
> >> to virtio_net, so we can negotiate support between the hypervisor
> >> and the guest.
> >>
> >> The signalling to the guest that an alternate checksum needs to
> >> be used is done via a new flag in the virtio_net_hdr.  If the
> >> flag is set, the host will know to perform an alternate checksum
> >> calculation, which right now is only CRC32c.
> >>
> >> Signed-off-by: Vladislav Yasevich <vyasevic at redhat.com>
> >> ---
> >>  drivers/net/virtio_net.c        | 11 ++++++++---
> >>  include/linux/virtio_net.h      |  6 ++++++
> >>  include/uapi/linux/virtio_net.h |  2 ++
Could you pls include a virtio TC mailing list on uapi changes?
> >>  3 files changed, 16 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> >> index 7b187ec..b601294 100644
> >> --- a/drivers/net/virtio_net.c
> >> +++ b/drivers/net/virtio_net.c
> >> @@ -2724,9 +2724,14 @@ static int virtnet_probe(struct
virtio_device *vdev)
> >>  	/* Do we support "hardware" checksums? */
> >>  	if (virtio_has_feature(vdev, VIRTIO_NET_F_CSUM)) {
> >>  		/* This opens up the world of extra features. */
> >> -		dev->hw_features |= NETIF_F_HW_CSUM | NETIF_F_SG;
> >> +		netdev_features_t sctp = 0;
> >> +
> >> +		if (virtio_has_feature(vdev, VIRTIO_NET_F_SCTP_CSUM))
> >> +			sctp |= NETIF_F_SCTP_CRC;
> >> +
> >> +		dev->hw_features |= NETIF_F_HW_CSUM | NETIF_F_SG | sctp;
> >>  		if (csum)
> >> -			dev->features |= NETIF_F_HW_CSUM | NETIF_F_SG;
> >> +			dev->features |= NETIF_F_HW_CSUM | NETIF_F_SG | sctp;
> >>  
> >>  		if (virtio_has_feature(vdev, VIRTIO_NET_F_GSO)) {
> >>  			dev->hw_features |= NETIF_F_TSO
> >> @@ -2952,7 +2957,7 @@ static struct virtio_device_id id_table[] =
{
> >>  };
> >>  
> >>  #define VIRTNET_FEATURES \
> >> -	VIRTIO_NET_F_CSUM, VIRTIO_NET_F_GUEST_CSUM, \
> >> +	VIRTIO_NET_F_CSUM, VIRTIO_NET_F_GUEST_CSUM, 
VIRTIO_NET_F_SCTP_CSUM, \
> >>  	VIRTIO_NET_F_MAC, \
> >>  	VIRTIO_NET_F_HOST_TSO4, VIRTIO_NET_F_HOST_UFO,
VIRTIO_NET_F_HOST_TSO6, \
> >>  	VIRTIO_NET_F_HOST_ECN, VIRTIO_NET_F_GUEST_TSO4,
VIRTIO_NET_F_GUEST_TSO6, \
> >> diff --git a/include/linux/virtio_net.h
b/include/linux/virtio_net.h
> >> index f144216..2e7a64a 100644
> >> --- a/include/linux/virtio_net.h
> >> +++ b/include/linux/virtio_net.h
> >> @@ -39,6 +39,9 @@ static inline int virtio_net_hdr_to_skb(struct
sk_buff *skb,
> >>  
> >>  		if (!skb_partial_csum_set(skb, start, off))
> >>  			return -EINVAL;
> >> +
> >> +		if (hdr->flags & VIRTIO_NET_HDR_F_CSUM_NOT_INET)
> >> +			skb->csum_not_inet = 1;
> >>  	}
> >>  
> >>  	if (hdr->gso_type != VIRTIO_NET_HDR_GSO_NONE) {
> >> @@ -96,6 +99,9 @@ static inline int virtio_net_hdr_from_skb(const
struct sk_buff *skb,
> >>  		hdr->flags = VIRTIO_NET_HDR_F_DATA_VALID;
> >>  	} /* else everything is zero */
> >>  
> >> +	if (skb->csum_not_inet)
> >> +		hdr->flags &= VIRTIO_NET_HDR_F_CSUM_NOT_INET;
> >> +
> >>  	return 0;
> >>  }
> >>  
> >> diff --git a/include/uapi/linux/virtio_net.h
b/include/uapi/linux/virtio_net.h
> >> index 5de6ed3..3f279c8 100644
> >> --- a/include/uapi/linux/virtio_net.h
> >> +++ b/include/uapi/linux/virtio_net.h
> >> @@ -36,6 +36,7 @@
> >>  #define VIRTIO_NET_F_GUEST_CSUM	1	/* Guest handles pkts w/
partial csum */
> >>  #define VIRTIO_NET_F_CTRL_GUEST_OFFLOADS 2 /* Dynamic offload
configuration. */
> >>  #define VIRTIO_NET_F_MTU	3	/* Initial MTU advice */
> >> +#define VIRTIO_NET_F_SCTP_CSUM  4	/* SCTP checksum offload
support */
> >>  #define VIRTIO_NET_F_MAC	5	/* Host has given MAC address. */
> >>  #define VIRTIO_NET_F_GUEST_TSO4	7	/* Guest can handle TSOv4 in.
*/
> >>  #define VIRTIO_NET_F_GUEST_TSO6	8	/* Guest can handle TSOv6 in.
*/
> > 
> > Is this a guest or a host checksum? We should differenciate between
the
> > two.
> 
> I suppose this is HOST checksum, since it behaves like VIRTIO_NET_F_CSUM
only for
> SCTP.  I couldn't find the use for the GUEST side flag, since there
technically
> isn't any validations and there is no additional mappings from VIRTIO
flag to a
> NETIF flag.
> 
> If the feature is negotiated, the guest ends up generating partially
check-summed
> packets, and the host turns on appropriate flags on it's side.   The
host will
> also make sure the checksum if fixed up if the guest doesn't support
it.
> So 1 flag is currently all that is needed.
> 
> -vlad
Fine, but let's include HOST in there to make things clear.
Also I think we should use a high flag, like 62.
> > 
> > 
> >> @@ -101,6 +102,7 @@ struct virtio_net_config {
> >>  struct virtio_net_hdr_v1 {
> >>  #define VIRTIO_NET_HDR_F_NEEDS_CSUM	1	/* Use csum_start,
csum_offset */
> >>  #define VIRTIO_NET_HDR_F_DATA_VALID	2	/* Csum is valid */
> >> +#define VIRTIO_NET_HDR_F_CSUM_NOT_INET  4       /* Checksum is
not inet */
> >>  	__u8 flags;
> >>  #define VIRTIO_NET_HDR_GSO_NONE		0	/* Not a GSO frame */
> >>  #define VIRTIO_NET_HDR_GSO_TCPV4	1	/* GSO frame, IPv4 TCP (TSO)
*/

> >> -- 
> >> 2.9.5

Michael S. Tsirkin

2018-Apr-16 17:09 UTC

head link

[PATCH net-next 1/5] virtio: Add support for SCTP checksum offloading

On Mon, Apr 16, 2018 at 09:45:48AM -0400, Vlad Yasevich
wrote:> On 04/11/2018 06:49 PM, Michael S. Tsirkin wrote:
> > On Mon, Apr 02, 2018 at 09:40:02AM -0400, Vladislav Yasevich wrote:
> >> To support SCTP checksum offloading, we need to add a new feature
> >> to virtio_net, so we can negotiate support between the hypervisor
> >> and the guest.
> >>
> >> The signalling to the guest that an alternate checksum needs to
> >> be used is done via a new flag in the virtio_net_hdr.  If the
> >> flag is set, the host will know to perform an alternate checksum
> >> calculation, which right now is only CRC32c.
> >>
> >> Signed-off-by: Vladislav Yasevich <vyasevic at redhat.com>
> >> ---
> >>  drivers/net/virtio_net.c        | 11 ++++++++---
> >>  include/linux/virtio_net.h      |  6 ++++++
> >>  include/uapi/linux/virtio_net.h |  2 ++
> >>  3 files changed, 16 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> >> index 7b187ec..b601294 100644
> >> --- a/drivers/net/virtio_net.c
> >> +++ b/drivers/net/virtio_net.c
> >> @@ -2724,9 +2724,14 @@ static int virtnet_probe(struct
virtio_device *vdev)
> >>  	/* Do we support "hardware" checksums? */
> >>  	if (virtio_has_feature(vdev, VIRTIO_NET_F_CSUM)) {
> >>  		/* This opens up the world of extra features. */
> >> -		dev->hw_features |= NETIF_F_HW_CSUM | NETIF_F_SG;
> >> +		netdev_features_t sctp = 0;
> >> +
> >> +		if (virtio_has_feature(vdev, VIRTIO_NET_F_SCTP_CSUM))
> >> +			sctp |= NETIF_F_SCTP_CRC;
> >> +
> >> +		dev->hw_features |= NETIF_F_HW_CSUM | NETIF_F_SG | sctp;
> >>  		if (csum)
> >> -			dev->features |= NETIF_F_HW_CSUM | NETIF_F_SG;
> >> +			dev->features |= NETIF_F_HW_CSUM | NETIF_F_SG | sctp;
> >>  
> >>  		if (virtio_has_feature(vdev, VIRTIO_NET_F_GSO)) {
> >>  			dev->hw_features |= NETIF_F_TSO
> >> @@ -2952,7 +2957,7 @@ static struct virtio_device_id id_table[] =
{
> >>  };
> >>  
> >>  #define VIRTNET_FEATURES \
> >> -	VIRTIO_NET_F_CSUM, VIRTIO_NET_F_GUEST_CSUM, \
> >> +	VIRTIO_NET_F_CSUM, VIRTIO_NET_F_GUEST_CSUM, 
VIRTIO_NET_F_SCTP_CSUM, \
> >>  	VIRTIO_NET_F_MAC, \
> >>  	VIRTIO_NET_F_HOST_TSO4, VIRTIO_NET_F_HOST_UFO,
VIRTIO_NET_F_HOST_TSO6, \
> >>  	VIRTIO_NET_F_HOST_ECN, VIRTIO_NET_F_GUEST_TSO4,
VIRTIO_NET_F_GUEST_TSO6, \
> >> diff --git a/include/linux/virtio_net.h
b/include/linux/virtio_net.h
> >> index f144216..2e7a64a 100644
> >> --- a/include/linux/virtio_net.h
> >> +++ b/include/linux/virtio_net.h
> >> @@ -39,6 +39,9 @@ static inline int virtio_net_hdr_to_skb(struct
sk_buff *skb,
> >>  
> >>  		if (!skb_partial_csum_set(skb, start, off))
> >>  			return -EINVAL;
> >> +
> >> +		if (hdr->flags & VIRTIO_NET_HDR_F_CSUM_NOT_INET)
> >> +			skb->csum_not_inet = 1;
> >>  	}
> >>  
> >>  	if (hdr->gso_type != VIRTIO_NET_HDR_GSO_NONE) {
> >> @@ -96,6 +99,9 @@ static inline int virtio_net_hdr_from_skb(const
struct sk_buff *skb,
> >>  		hdr->flags = VIRTIO_NET_HDR_F_DATA_VALID;
> >>  	} /* else everything is zero */
> >>  
> >> +	if (skb->csum_not_inet)
> >> +		hdr->flags &= VIRTIO_NET_HDR_F_CSUM_NOT_INET;
> >> +
> >>  	return 0;
> >>  }
> >>  
> >> diff --git a/include/uapi/linux/virtio_net.h
b/include/uapi/linux/virtio_net.h
> >> index 5de6ed3..3f279c8 100644
> >> --- a/include/uapi/linux/virtio_net.h
> >> +++ b/include/uapi/linux/virtio_net.h
> >> @@ -36,6 +36,7 @@
> >>  #define VIRTIO_NET_F_GUEST_CSUM	1	/* Guest handles pkts w/
partial csum */
> >>  #define VIRTIO_NET_F_CTRL_GUEST_OFFLOADS 2 /* Dynamic offload
configuration. */
> >>  #define VIRTIO_NET_F_MTU	3	/* Initial MTU advice */
> >> +#define VIRTIO_NET_F_SCTP_CSUM  4	/* SCTP checksum offload
support */
> >>  #define VIRTIO_NET_F_MAC	5	/* Host has given MAC address. */
> >>  #define VIRTIO_NET_F_GUEST_TSO4	7	/* Guest can handle TSOv4 in.
*/
> >>  #define VIRTIO_NET_F_GUEST_TSO6	8	/* Guest can handle TSOv6 in.
*/
> > 
> > Is this a guest or a host checksum? We should differenciate between
the
> > two.
> 
> I suppose this is HOST checksum, since it behaves like VIRTIO_NET_F_CSUM
only for
> SCTP.  I couldn't find the use for the GUEST side flag, since there
technically
> isn't any validations and there is no additional mappings from VIRTIO
flag to a
> NETIF flag.
> 
> If the feature is negotiated, the guest ends up generating partially
check-summed
> packets, and the host turns on appropriate flags on it's side.   The
host will
> also make sure the checksum if fixed up if the guest doesn't support
it.
> So 1 flag is currently all that is needed.
> 
> -vlad
I see code handling VIRTIO_NET_HDR_F_CSUM_NOT_INET on RX side.  Host
needs to know whether it's ok/worth it to set this flag, too.
> > 
> > 
> >> @@ -101,6 +102,7 @@ struct virtio_net_config {
> >>  struct virtio_net_hdr_v1 {
> >>  #define VIRTIO_NET_HDR_F_NEEDS_CSUM	1	/* Use csum_start,
csum_offset */
> >>  #define VIRTIO_NET_HDR_F_DATA_VALID	2	/* Csum is valid */
> >> +#define VIRTIO_NET_HDR_F_CSUM_NOT_INET  4       /* Checksum is
not inet */
> >>  	__u8 flags;
> >>  #define VIRTIO_NET_HDR_GSO_NONE		0	/* Not a GSO frame */
> >>  #define VIRTIO_NET_HDR_GSO_TCPV4	1	/* GSO frame, IPv4 TCP (TSO)
*/
> >> -- 
> >> 2.9.5

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