centos man page for skb_copy_expand

SKB_COPY_EXPAND(9)						 Linux Networking						SKB_COPY_EXPAND(9)

NAME
       skb_copy_expand - copy and expand sk_buff

SYNOPSIS
       struct sk_buff * skb_copy_expand(const struct sk_buff * skb, int newheadroom, int newtailroom, gfp_t gfp_mask);

ARGUMENTS
       skb
	   buffer to copy

       newheadroom
	   new free bytes at head

       newtailroom
	   new free bytes at tail

       gfp_mask
	   allocation priority

DESCRIPTION
       Make a copy of both an sk_buff and its data and while doing so allocate additional space.

       This is used when the caller wishes to modify the data and needs a private copy of the data to alter as well as more space for new fields.
       Returns NULL on failure or the pointer to the buffer on success. The returned buffer has a reference count of 1.

       You must pass GFP_ATOMIC as the allocation priority if this function is called from an interrupt.

COPYRIGHT
Kernel Hackers Manual 3.10					     June 2014							SKB_COPY_EXPAND(9)