Some/most devices implementing gso_partial need to disable the GSO partial
features when the IP ID can't be mangled; to that extend each of them
implements something alike the following:

	if (skb->encapsulation && !(features & NETIF_F_TSO_MANGLEID))
		features &= ~NETIF_F_TSO;

in the ndo_features_check() op, which leads to a bit of duplicate code.

Later patch in the series will implement GSO partial support for virtual
device, and the current status quo will require more duplicate code and
a new indirect call in the TX path for such devices.

Introduce the mangleid_features mask, allowing the core to disable NIC
features based on/requiring MANGLEID, without any further intervention
from the driver.

The same functionality could be alternatively implemented adding a single
boolean flag to the struct net_device, but would require an additional
checks in ndo_features_check().

Also note that the above mentioned action is incorrect if the NIC
additionally implements NETIF_F_GSO_UDP_L4, mangleid_features
transparently handle even such a case.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
 include/linux/netdevice.h | 5 ++++-
 net/core/dev.c            | 4 +++-
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index d99b0fbc1942..23a698b70de1 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h

@@ -1830,7 +1830,9 @@ enum netdev_reg_state {
  *				and drivers will need to set them appropriately.
  *
  *	@mpls_features:	Mask of features inheritable by MPLS
- *	@gso_partial_features: value(s) from NETIF_F_GSO\*
+ *	@gso_partial_features: value(s) from NETIF_F_GSO
+ *	@mangleid_features:	Mask of features requiring MANGLEID, will be
+ *				disabled together with the latter.
  *
  *	@ifindex:	interface index
  *	@group:		The group the device belongs to

@@ -2219,6 +2221,7 @@ struct net_device {
 	netdev_features_t	vlan_features;
 	netdev_features_t	hw_enc_features;
 	netdev_features_t	mpls_features;
+	netdev_features_t	mangleid_features;
 
 	unsigned int		min_mtu;
 	unsigned int		max_mtu;

diff --git a/net/core/dev.c b/net/core/dev.c
index c711da335510..6154f306ed76 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c

@@ -3788,8 +3788,10 @@ static netdev_features_t gso_features_check(const struct sk_buff *skb,
 		struct iphdr *iph = skb->encapsulation ?
 				    inner_ip_hdr(skb) : ip_hdr(skb);
 
-		if (!(iph->frag_off & htons(IP_DF)))
+		if (!(iph->frag_off & htons(IP_DF))) {
 			features &= ~NETIF_F_TSO_MANGLEID;
+			features &= ~dev->mangleid_features;
+		}
 	}
 
 	/* NETIF_F_IPV6_CSUM does not support IPv6 extension headers,

-- 
2.52.0