skb_cow(9) [centos man page]

SKB_COW(9)							 Linux Networking							SKB_COW(9)

NAME

       skb_cow - copy header of skb when it is required

SYNOPSIS

       int skb_cow(struct sk_buff * skb, unsigned int headroom);

ARGUMENTS

       skb
	   buffer to cow

       headroom
	   needed headroom

DESCRIPTION

       If the skb passed lacks sufficient headroom or its data part is shared, data is reallocated. If reallocation fails, an error is returned
       and original skb is not changed.

       The result is skb with writable area skb->head...skb->tail and at least headroom of space at head.

COPYRIGHT

Kernel Hackers Manual 3.10					     June 2014								SKB_COW(9)

STRUCT 
SK_BUFF(9)						 Linux Networking						 STRUCT SK_BUFF(9)

NAME

       struct_sk_buff - socket buffer

SYNOPSIS

       struct sk_buff {
	 struct sk_buff * next;
	 struct sk_buff * prev;
	 ktime_t tstamp;
	 struct sock * sk;
	 struct net_device * dev;
	 char cb[48];
	 unsigned long _skb_dst;
       #ifdef CONFIG_XFRM
	 struct sec_path * sp;
       #endif
	 unsigned int len;
	 unsigned int data_len;
	 __u16 mac_len;
	 __u16 hdr_len;
	 union {unnamed_union};
	 __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;
	 unsigned char * data;
	 unsigned int truesize;
	 atomic_t users;
       };

MEMBERS

       next
	   Next buffer in list

       prev
	   Previous buffer in list

       tstamp
	   Time we arrived

       sk
	   Socket we are owned by

       dev
	   Device we arrived on/are leaving by

       cb[48]
	   Control buffer. Free for use by every layer. Put private vars here

       _skb_dst
	   destination entry

       sp
	   the security path, used for xfrm

       len
	   Length of actual data

       data_len
	   Data length

       mac_len
	   Length of link layer header

       hdr_len
	   writable header length of cloned skb

       {unnamed_union}
	   anonymous

       vlan_tci
	   vlan tag control information

       transport_header
	   Transport layer header

       network_header
	   Network layer header

       mac_header
	   Link layer header

       tail
	   Tail pointer

       end
	   End pointer

       head
	   Head of buffer

       data
	   Data head pointer

       truesize
	   Buffer size

       users
	   User count - see {datagram,tcp}.c

COPYRIGHT

Kernel Hackers Manual 2.6.					     July 2010							 STRUCT SK_BUFF(9)