Subject: Re: [PATCH: dtc] Improve -S handling

From: David Gibson <[email-masked]>
Date: Thu, 19 Apr 2007 10:18:10 +1000

On Wed, Apr 18, 2007 at 08:27:34AM -0400, Jerry Van Baren wrote:
> David Gibson wrote:
> > On Wed, Apr 18, 2007 at 01:05:28PM +1000, David Gibson wrote:
> >> On Tue, Apr 17, 2007 at 10:05:35PM -0400, Jerry Van Baren wrote:
> >>> If the user requests extra space, pad out the blob (previously the unused
> >>>   data was undefined).
> >>>
> >>> Signed-off-by: Gerald Van Baren <[email-masked]>
> >>> ---
> >>>
> >>> Hi Jon, David, Milton,
> >>>
> >>> This improves the -S option to pad out the blob with zeros when the user
> >>> asks for extra space.
> >> Comment below
> >>> diff --git a/flattree.c b/flattree.c
> >>> index 151d16e..d2ee0dc 100644
> >>> --- a/flattree.c
> >>> +++ b/flattree.c
> >>> @@ -310,6 +310,7 @@ static struct data flatten_reserve_list(struct reserve_info *reservelist,
> >>>  	
> >>>  	return d;
> >>>  }
> >>> +
> >>>  static void make_bph(struct boot_param_header *bph,
> >>>  		     struct version_info *vi,
> >>>  		     int reservesize, int dtsize, int strsize,
> >>> @@ -358,12 +359,15 @@ void dt_to_blob(FILE *f, struct boot_info *bi, int version,
> >>>  {
> >>>  	struct version_info *vi = NULL;
> >>>  	int i;
> >>> +	int size;
> >>>  	struct data dtbuf = empty_data;
> >>>  	struct data strbuf = empty_data;
> >>>  	struct data reservebuf;
> >>>  	struct boot_param_header bph;
> >>>  	struct reserve_entry termre = {.address = 0, .size = 0};
> >>>  
> >>> +	size = 0;
> >>> +
> > 
> > Oh, also, you shouldn't need this new variable to track the size.
> > Just use whatever expression we used to use for totalsize before we
> > forced it out to the minimum size.
> 
> It was simpler that way.  Much simpler.  With the calculated version, I 
> had to know the header size and re-calculate all the alignment gaps. 
> Ugly and nasty (respectively and collectively).

Hrm.. but we already did all that calculation in make_bph().

Here's a revised idea: with -S, instead of overriding the totalsize
header field directly in make_bph(), instead revert that function to
always computing the "natural minimum" size of the blob.  Then do the
-S handling in dt_to_blob() instead: compute the number of padding
bytes necessary from make_bph()'s totalsize value, then overwrite the
totalsize field with the expanded value.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson