linux networking at kernel level
Hi all, i'm a newbie of this list
i'm studying linux kernel 18.104.22.168 sourcecode for my thesis because
i've to create a kernel module that reads and writes tcp/ip packets;
for example i've to read infos from tcp and ip header and then route
to destination through an interface that i want from those that i've
installed on my pc (wireless, ethernet...) .
my work is similar to some phrack article - but that are for
very old kernels (2.2 or 2.4 series) so i can't use them at all.
i've found more recent document  that uses 22.214.171.124 kernel source
but the same functions now request another parameter that is a "struct
net * " .
i've done a simple test module that drop all packets incoming by
pre_hook.hook = watch_in; // this function
pre_hook.pf = PF_INET;
pre_hook.priority = NF_IP_PRI_FIRST;
pre_hook.hooknum = NF_INET_PRE_ROUTING;
but i can't make an ip address filter dropping.
now, my questions are:
- in  there is "dev_get" function that return a struct device from
a char* , in newer kernels i've found "dev_get_by_name" but that
function wants a "struct net *": it has to be a newly defined struct
or i've to to get existent one? if i've to to get existent one, how
can i do that ?
same question about "struct net *" for "for_each_netdev" function used
- to use "for_each_netdev" as told above, i can't use *dev_net
function, defined in netdevice.h, to find a "struct net" from "struct
net_device" because it wants a *net_device (i'm inside a loop!).
- how can i read information in received packet ?
for example, to read the source ip address of a received packet, i've
to do only "ip_hdr(skb)->saddr" ?
can i print it on /var/log/messages ?
- if i want to write in the same field of outgoing packet can i use
"ip_hdr(skb)->saddr" again or there is a defined function to do this ?
 "building inte the linux kernel network driver"
 "hacking the linux kernel network stack"
Thank you for your answers!