dhcpcd-discuss

On 05/04/2013 21:03, jayce lee wrote:
> I got to read the source code and came up with some confusion. Could
> you please give me some help.
>
> in the structure if_options
>
> struct if_options {
>  int metric;
>  uint8_t requestmask[256 / 8];
>  uint8_t requiremask[256 / 8];
>  uint8_t nomask[256 / 8];
>  uint8_t requestmask6[(UINT16_MAX + 1) / 8];
>  uint8_t requiremask6[(UINT16_MAX + 1) / 8];
>  uint8_t nomask6[(UINT16_MAX + 1) / 8];
>         ……
> }
>
> there are some masks, what's the function of the mask and why for
> ipv4 the size of mask is 256/8 and for ipv6 the size is UINT16_MAX + 
> 1
> /8 ?
>
>  By the way, in the parse_config process, the function
> make_option_mask change the mask value in
> add_option_mask(mask,opt->option);
> The macro definition is #define add_option_mask(var, val) (var[val >>
> 3] |= 1 << (val & 7)), I can't quite get the purpose of the source
> code. 
>
> Could someone give me explanations?

We store the presence or non presence of DHCP or DHCPv6 options in a 
bit mask.
The macros allow easy access to it via bit shifting.

Thanks

Roy