dhcpcd-discuss

On 19/04/2013 12:09, jayce lee wrote:
> In lpf.c, dhcpcd declares a variable named su.
>
>  union sockunion {
>  struct sockaddr sa;
>  struct sockaddr_in sin;
>  struct sockaddr_ll sll;
>  struct sockaddr_storage ss;
>  } su;
>
> It only initialize the su.sll, but in the action of bind, the socket
> fd bind to su.sa [1] with the addr_len of sizeof(su).
>
> I'm confusing why we need a sockunion and bind to su.sa [1] with the
> length of sizeof(su)?

It's how we pass sockaddr_ll to bind as bind only accepts sockaddr_sa.
It's an elegant method which avoids needless casting.

See here for a more complete answer:
http://stackoverflow.com/questions/1429645/how-to-cast-sockaddr-storage-and-avoid-breaking-strict-aliasing-rules

Thanks

Roy