af_packet: pass checksum validation status to the user

Introduce TP_STATUS_CSUM_VALID tp_status flag to tell the
af_packet user that at least the transport header checksum
has been already validated.

For now, the flag may be set for incoming packets only.

Signed-off-by: Alexander Drozdov <[e-mail]>
Cc: Willem de Bruijn <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

Documentation/networking/packet_mmap.txt

···
 +++ Capture process:
      from include/linux/if_packet.h
 
-     #define TP_STATUS_COPY          2 
-     #define TP_STATUS_LOSING        4 
-     #define TP_STATUS_CSUMNOTREADY  8 
+     #define TP_STATUS_COPY          (1 << 1)
+     #define TP_STATUS_LOSING        (1 << 2)
+     #define TP_STATUS_CSUMNOTREADY  (1 << 3)
+     #define TP_STATUS_CSUM_VALID    (1 << 7)
 
 TP_STATUS_COPY        : This flag indicates that the frame (and associated
                         meta information) has been truncated because it's 
···
                         its checksum will be done in hardware. So while
                         reading the packet we should not try to check the 
                         checksum. 
+
+TP_STATUS_CSUM_VALID  : This flag indicates that at least the transport
+                        header checksum of the packet has been already
+                        validated on the kernel side. If the flag is not set
+                        then we are free to check the checksum by ourselves
+                        provided that TP_STATUS_CSUMNOTREADY is also not set.
 
 for convenience there are also the following defines:
 

include/uapi/linux/if_packet.h

···
 #define TP_STATUS_VLAN_VALID		(1 << 4) /* auxdata has valid tp_vlan_tci */
 #define TP_STATUS_BLK_TMO		(1 << 5)
 #define TP_STATUS_VLAN_TPID_VALID	(1 << 6) /* auxdata has valid tp_vlan_tpid */
+#define TP_STATUS_CSUM_VALID		(1 << 7)
 
 /* Tx ring - header status */
 #define TP_STATUS_AVAILABLE	      0

net/packet/af_packet.c

···
 
 	if (skb->ip_summed == CHECKSUM_PARTIAL)
 		status |= TP_STATUS_CSUMNOTREADY;
+	else if (skb->pkt_type != PACKET_OUTGOING &&
+		 (skb->ip_summed == CHECKSUM_COMPLETE ||
+		  skb_csum_unnecessary(skb)))
+		status |= TP_STATUS_CSUM_VALID;
 
 	if (snaplen > res)
 		snaplen = res;
···
 		aux.tp_status = TP_STATUS_USER;
 		if (skb->ip_summed == CHECKSUM_PARTIAL)
 			aux.tp_status |= TP_STATUS_CSUMNOTREADY;
+		else if (skb->pkt_type != PACKET_OUTGOING &&
+			 (skb->ip_summed == CHECKSUM_COMPLETE ||
+			  skb_csum_unnecessary(skb)))
+			aux.tp_status |= TP_STATUS_CSUM_VALID;
+
 		aux.tp_len = origlen;
 		aux.tp_snaplen = skb->len;
 		aux.tp_mac = 0;