+/* A. Checksumming of received packets by device.
+ *
+ * CHECKSUM_NONE:
+ *
+ * Device failed to checksum this packet e.g. due to lack of capabilities.
+ * The packet contains full (though not verified) checksum in packet but
+ * not in skb->csum. Thus, skb->csum is undefined in this case.
+ *
+ * CHECKSUM_UNNECESSARY:
+ *
+ * The hardware you're dealing with doesn't calculate the full checksum
+ * (as in CHECKSUM_COMPLETE), but it does parse headers and verify checksums
+ * for specific protocols e.g. TCP/UDP/SCTP, then, for such packets it will
+ * set CHECKSUM_UNNECESSARY if their checksums are okay. skb->csum is still
+ * undefined in this case though. It is a bad option, but, unfortunately,
+ * nowadays most vendors do this. Apparently with the secret goal to sell
+ * you new devices, when you will add new protocol to your host, f.e. IPv6 8)
+ *
+ * CHECKSUM_COMPLETE:
+ *
+ * This is the most generic way. The device supplied checksum of the _whole_
+ * packet as seen by netif_rx() and fills out in skb->csum. Meaning, the
+ * hardware doesn't need to parse L3/L4 headers to implement this.
+ *
+ * Note: Even if device supports only some protocols, but is able to produce
+ * skb->csum, it MUST use CHECKSUM_COMPLETE, not CHECKSUM_UNNECESSARY.
+ *
+ * CHECKSUM_PARTIAL:
+ *
+ * This is identical to the case for output below. This may occur on a packet
+ * received directly from another Linux OS, e.g., a virtualized Linux kernel
+ * on the same host. The packet can be treated in the same way as
+ * CHECKSUM_UNNECESSARY, except that on output (i.e., forwarding) the
+ * checksum must be filled in by the OS or the hardware.
+ *
+ * B. Checksumming on output.
+ *
+ * CHECKSUM_NONE:
+ *
+ * The skb was already checksummed by the protocol, or a checksum is not
+ * required.
+ *
+ * CHECKSUM_PARTIAL:
+ *
+ * The device is required to checksum the packet as seen by hard_start_xmit()
+ * from skb->csum_start up to the end, and to record/write the checksum at
+ * offset skb->csum_start + skb->csum_offset.
+ *
+ * The device must show its capabilities in dev->features, set up at device
+ * setup time, e.g. netdev_features.h:
+ *
+ * NETIF_F_HW_CSUM - It's a clever device, it's able to checksum everything.
+ * NETIF_F_IP_CSUM - Device is dumb, it's able to checksum only TCP/UDP over
+ * IPv4. Sigh. Vendors like this way for an unknown reason.
+ * Though, see comment above about CHECKSUM_UNNECESSARY. 8)
+ * NETIF_F_IPV6_CSUM - About as dumb as the last one but does IPv6 instead.
+ * NETIF_F_... - Well, you get the picture.
+ *
+ * CHECKSUM_UNNECESSARY:
+ *
+ * Normally, the device will do per protocol specific checksumming. Protocol
+ * implementations that do not want the NIC to perform the checksum
+ * calculation should use this flag in their outgoing skbs.
+ *
+ * NETIF_F_FCOE_CRC - This indicates that the device can do FCoE FC CRC
+ * offload. Correspondingly, the FCoE protocol driver
+ * stack should use CHECKSUM_UNNECESSARY.
+ *
+ * Any questions? No questions, good. --ANK
+ */
+