nf_trace:1;
kmemcheck_bitfield_end(flags1);
__be16 protocol;
void (*destructor)(struct sk_buff *skb);
#if defined(CONFIG_NF_CONNTRACK) || defined(CONFIG_NF_CONNTRACK_MODULE)
struct nf_conntrack *nfct;
struct sk_buff *nfct_reasm;
#endif
#ifdef CONFIG_BRIDGE_NETFILTER
struct nf_bridge_info *nf_bridge;
#endif
int skb_iif;
#ifdef CONFIG_NET_SCHED
__u16 tc_index;
#ifdef CONFIG_NET_CLS_ACT
__u16 tc_verd;
#endif
#endif
__u32 rxhash;
kmemcheck_bitfield_begin(flags2);
__u16 queue_mapping:16;
#ifdef CONFIG_IPV6_NDISC_NODETYPE
__u8 ndisc_nodetype:2,
deliver_no_wcard:1;
#else
__u8 deliver_no_wcard:1;
#endif
kmemcheck_bitfield_end(flags2);
#ifdef CONFIG_NET_DMA
dma_cookie_t dma_cookie;
#endif
#ifdef CONFIG_NETWORK_SECMARK
__u32 secmark;
#endif
union {
__u32 mark;
__u32 dropcount;
};
__u16 vlan_tci;
sk_buff_data_t transport_header;
sk_buff_data_t network_header;
sk_buff_data_t mac_header;
sk_buff_data_t tail;
sk_buff_data_t end;
unsigned char *head,
*data;
unsigned int truesize;
atomic_t users;
};
元素的含义如下（摘自内核,源码,版本2.6.35.4）
*struct sk_buff - socket buffer
* @next: Next buffer inlist
* @prev: Previous buffer in list
* @sk: Socketwe are owned by
* @tstamp: Time we arrived
* @dev:Device we arrived on/are leaving by
* @transport_header:Transport layer header
* @network_header: Network layerheader
* @mac_header: Link layer header
*@_skb_refdst: destination entry (with norefcount bit)
* @sp:the security path, used for xfrm
* @cb: Control buffer. Freefor use by every layer. Put private vars here
* @len: Lengthof actual data
* @data_len: Data length
* @mac_len:Length of link layer header
* @hdr_len: writable headerlength of cloned skb
* @csum: Checksum (must includestart/offset pair)
* @csum_start: Offset from skb->headwhere checksumming should start
* @csum_offset: Offset fromcsum_start where checksum should be stored
* @local_df:allow local fragmentation
* @cloned: Head may be cloned(check refcnt to be sure)
* @nohdr: Payload reference only,must not modify header
* @pkt_type: Packet class
*@fclone: skbuff clone status
* @ip_summed: Driver fed us anIP checksum
* @priority: Packet queueing priority
*@users: User count - see {datagram,tcp}.c
* @protocol:Packet protocol from driver
* @truesize: Buffer size
*@head: Head of buffer
* @data: Data head pointer
*@tail: Tail pointer
* @end: End pointer
*@destructor: Destruct function
* @mark: Generic packetmark
* @nfct: Associated connection, if any
*@ipvs_property: skbuff is owned by ipvs
* @peeked: thispacket has been seen already, so stats have been
* done forit, dont do them again
* @nf_trace: netfilter packet traceflag
* @nfctinfo: Relationship of this skb to theconnection
* @nfct_reasm: netfilter conntrack re-assemblypointer
* @nf_bridge: Saved data about a bridged frame - seebr_netfilter.c
* @skb_iif: ifindex of device we arrivedon
* @rxhash: the packet hash computed on receive
*@queue_mapping: Queue mapping for multiqueue devices
*@tc_index: Traffic control index
* @tc_verd: traffic controlverdict
* @ndisc_nodetype: router type (from link layer)
*@dma_cookie: a cookie to one of several possible DMA operations
*done by skb DMA functions
* @secmark: security marking
*@vlan_tci: vlan tag control information
关于sk_buff的更多分析见另一篇转载的博文http://blog.csdn.net/yming0221/article/details/6609734
4.2
