diff options
Diffstat (limited to 'include/linux/skbuff.h')
| -rw-r--r-- | include/linux/skbuff.h | 131 |
1 files changed, 75 insertions, 56 deletions
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h index 06bedeb0d49e..c5cd016f5120 100644 --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -34,11 +34,82 @@ #include <linux/netdev_features.h> #include <net/flow_keys.h> +/* 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 + */ + /* Don't change this without changing skb_csum_unnecessary! */ -#define CHECKSUM_NONE 0 -#define CHECKSUM_UNNECESSARY 1 -#define CHECKSUM_COMPLETE 2 -#define CHECKSUM_PARTIAL 3 +#define CHECKSUM_NONE 0 +#define CHECKSUM_UNNECESSARY 1 +#define CHECKSUM_COMPLETE 2 +#define CHECKSUM_PARTIAL 3 #define SKB_DATA_ALIGN(X) (((X) + (SMP_CACHE_BYTES - 1)) & \ ~(SMP_CACHE_BYTES - 1)) @@ -54,58 +125,6 @@ SKB_DATA_ALIGN(sizeof(struct sk_buff)) + \ SKB_DATA_ALIGN(sizeof(struct skb_shared_info))) -/* A. Checksumming of received packets by device. - * - * NONE: device failed to checksum this packet. - * skb->csum is undefined. - * - * UNNECESSARY: device parsed packet and wouldbe verified checksum. - * skb->csum is undefined. - * It is bad option, but, unfortunately, many of vendors do this. - * Apparently with secret goal to sell you new device, when you - * will add new protocol to your host. F.e. IPv6. 8) - * - * COMPLETE: the most generic way. Device supplied checksum of _all_ - * the packet as seen by netif_rx in skb->csum. - * NOTE: Even if device supports only some protocols, but - * is able to produce some skb->csum, it MUST use COMPLETE, - * not UNNECESSARY. - * - * PARTIAL: identical to the case for output below. This may occur - * on a packet received directly from another Linux OS, e.g., - * a virtualised Linux kernel on the same host. The packet can - * be treated in the same way as UNNECESSARY except that on - * output (i.e., forwarding) the checksum must be filled in - * by the OS or the hardware. - * - * B. Checksumming on output. - * - * NONE: skb is checksummed by protocol or csum is not required. - * - * PARTIAL: device is required to csum packet as seen by hard_start_xmit - * from skb->csum_start to the end and to record the checksum - * at skb->csum_start + skb->csum_offset. - * - * Device must show its capabilities in dev->features, set - * at device setup time. - * NETIF_F_HW_CSUM - it is clever device, it is able to checksum - * everything. - * NETIF_F_IP_CSUM - device is dumb. It is able to csum only - * TCP/UDP over IPv4. Sigh. Vendors like this - * way by 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. - * - * UNNECESSARY: device will do per protocol specific csum. Protocol drivers - * that do not want net to perform the checksum calculation should use - * this flag in their outgoing skbs. - * NETIF_F_FCOE_CRC this indicates the device can do FCoE FC CRC - * offload. Correspondingly, the FCoE protocol driver - * stack should use CHECKSUM_UNNECESSARY. - * - * Any questions? No questions, good. --ANK - */ - struct net_device; struct scatterlist; struct pipe_inode_info; |