dhcpd code changes

[Jeffrey Hutzelman]

--On Tuesday, November 10, 2009 05:21:14 PM +0530 Ashmath Khan 
<hashmat.email at gmail.com> wrote:

> Hi Jeffrey,

Please use the mailing list, rather than sending mail to me directly. 
There are lots of people there who can potentially help you and/or correct 
errors.  Sending privately to me means that those people don't get to see 
your message, and you get to wait until I have time to respond.  That may 
be a very long time -- if I don't have time to answer something the moment 
I see it, I may never get back to it.



> I couldn't figure out much about print_subexpression. I couldn't find from
> where this function is invoked.

>From itself, and from print_expression(), which is used for logging 
expressions for debugging purposes.  Contrary to my previous note, this is 
not actually used for dumping code to the leases file; write_expression() 
is used for that.

> Also I couldn't understand how are the magic numbers associated with
> 'len'. thanks.

They're not magic.  The 'len' parameter is the amount of space left in the 
output buffer.



>         if (*len *> 6) {

My code says "if (len > 6)".  It looks like you put ** around things here 
in an attempt to highlight them.  Don't do that -- it doesn't look like 
emphasis, and it _does_ change the meaning of the code.



>             rv = 4;
>             strcpy (buf, "(eq ");

Add 4 constant characters to the output

>             rv += print_subexpression (expr -> data.equal [0],
>                            buf + rv, len - rv - 2);

recursive call for the first subexpression, putting the output past the 
constant characters we already added and leaving room for the 2 we have not 
yet added.  Whatever space is left can be used to print the subexpression.

>             buf [rv++] = ' ';

Add another constant character

>             rv += print_subexpression (expr -> data.equal [1],
>                            buf + rv, len - rv - 1);

Another recursive call, this time leaving space only for the one character 
we haven't added yet.

>             buf [rv++] = ')';

Add the close paren.

>             buf [rv] = 0;
>             return rv;
>         }

This whole time, 'rv' has been the number of characters we added to the 
buffer.  That becomes the return value of print_subexpressioin.

-- Jeffrey T. Hutzelman (N3NHS) <jhutz+ at cmu.edu>
   Carnegie Mellon University - Pittsburgh, PA