Question

I am writing a kernel module and i have to compare to destination addresses..
I have an array of addresses to which i want to add these addresses dynamically. If the address is already in the array i drop it but if it is not i put it at the next available index.

A snipped of my code is as follows:

daddr = &udp_hdr(sock_buff)->dest; /* an example address just for comparison purposes */
saddr = &udp_hdr(sock_buff)->source; /* an example address just for comparison purposes */

int compare( __be32 addr1, __be32 addr2 ) {

  addr1[0] = 0xff & add1 >> 24;
  addr1[1] = 0xff & add1 >> 16;
  addr1[2] = 0xff & add1 >> 8;
  addr1[3] = 0xff & add1;

  addr2[0] = 0xff & add2 >> 24;
  addr2[1] = 0xff & add2 >> 16;
  addr2[2] = 0xff & add2 >> 8;
  addr2[3] = 0xff & add2;

  for(i=0; i<4; i++) {
    if(addr1[i]==addr2[i]) {;
      i++;
      if(i==4) {
        return 0;
        break;
      } else return 1;
    }
  }
} 

Then I’m comparing using the function

int compare( __be32 addr1, __be32 addr2 ) {

  addr1[0] = 0xff & add1 >> 24;
  addr1[1] = 0xff & add1 >> 16;
  addr1[2] = 0xff & add1 >> 8;
  addr1[3] = 0xff & add1;

  addr2[0] = 0xff & add2 >> 24;
  addr2[1] = 0xff & add2 >> 16;
  addr2[2] = 0xff & add2 >> 8;
  addr2[3] = 0xff & add2;

  for(i=0; i<4; i++) {
    if(addr1[i]==addr2[i]) {;
      i++;
      if(i==4) {
        return 0;
        break;
      } else return 1;
    }
  }
}

However, calling with function with say

compare((__be32)daddr, (__be32)saddr)

comparing addresses like 192.168.1.2 and 192.132.1.2 returns true (herein 0) and in some cases it returns false(herein 1). Where am I going wrong or is there a better way of comparing addresses?

Answer 1

you end up incrementing i i.e i++ twice if addr1[i] == addr2[i] also the else block is a suspect i guess what you need is

for(i=0; i<4; i++) {
   if(addr1[i]!=addr2[i]) {;
     return 1;
   }
}
return 0;