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

From: David Gibson <[email-masked]>
Date: Thu, 19 Apr 2007 11:42:24 +1000

On Wed, Apr 18, 2007 at 08:19:47AM -0400, Jerry Van Baren wrote:
> 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;
> >> +
> >>  	for (i = 0; i < ARRAY_SIZE(version_table); i++) {
> >>  		if (version_table[i].version == version)
> >>  			vi = &version_table[i];
> >> @@ -384,10 +388,13 @@ void dt_to_blob(FILE *f, struct boot_info *bi, int version,
> >>  		 boot_cpuid_phys);
> >>  
> >>  	fwrite(&bph, vi->hdr_size, 1, f);
> >> +	size += vi->hdr_size;
> >>  
> >>  	/* Align the reserve map to an 8 byte boundary */
> >> -	for (i = vi->hdr_size; i < be32_to_cpu(bph.off_mem_rsvmap); i++)
> >> +	for (i = vi->hdr_size; i < be32_to_cpu(bph.off_mem_rsvmap); i++) {
> >>  		fputc(0, f);
> >> +		size += 1;
> >> +	}
> >>  
> >>  	/*
> >>  	 * Reserve map entries.
> >> @@ -396,9 +403,27 @@ void dt_to_blob(FILE *f, struct boot_info *bi, int version,
> >>  	 */
> >>  	fwrite(reservebuf.val, reservebuf.len, 1, f);
> >>  	fwrite(&termre, sizeof(termre), 1, f);
> >> +	size += reservebuf.len + sizeof(termre);
> >>  
> >>  	fwrite(dtbuf.val, dtbuf.len, 1, f);
> >>  	fwrite(strbuf.val, strbuf.len, 1, f);
> >> +	size += dtbuf.len + strbuf.len;
> >> +
> >> +	/*
> >> +	 * If the user asked for more space than is used, pad it out.
> >> +	 */
> >> +	if (minsize > 0) {
> >> +		int padlen = minsize - size;
> >> +
> >> +		if (padlen > 0) {
> >> +			char *zeroes = calloc(padlen, 1);
> >> +
> >> +			if (zeroes != NULL) {
> >> +				fwrite(zeroes, padlen, 1, f);
> >> +				free(zeroes);
> >> +			}
> >> +		}
> >> +	}
> > 
> > Hrm, rather than all this explicit calloc() mangling, I'd prefer we
> > use our existing struct data stuff.  Use data_append_zeroes() on
> > empty_data to generate your buffer of padding.
> > 
> >>  	if (ferror(f))
> >>  		die("Error writing device tree blob: %s\n", strerror(errno));
> >> @@ -504,6 +529,14 @@ void dt_to_asm(FILE *f, struct boot_info *bi, int version, int boot_cpuid_phys)
> >>  
> >>  	emit_label(f, symprefix, "blob_end");
> >>  
> >> +	/*
> >> +	 * If the user asked for more space than is used, pad it out.
> >> +	 */
> >> +	if (minsize > 0) {
> >> +		fprintf(f, "\t.space\t%d - (%s_blob_end - %s_blob_start), 0\n", 
> >> +			minsize, symprefix, symprefix);
> >> +	}
> >> +
> >>  	data_free(strbuf);
> >>  }
> 
> Hi David,
> 
> I started down the data_append_zeroes() path and had to back up and take 
> the branch less traveled ;-).  The problem is that data_append_zeros() 
> appends the data to a "struct data" and I don't want to add zeros 
> internally to any of the existing pieces parts since the extra space is 
> external, not internal to the existing parts.
> 
> I suppose I could create a new "struct data zeroes" and use 
> data_append_zeroes() to create zeros in it, write that out, and then 
> free it, but I fail to see how that is better than simply calloc()ing a 
> bunch of zeros and writing _that_ out.

Hrm.  I suppose.  Though I do notice that your code will silently omit
the padding if the calloc() fails.

> P.S. David: I cannot send email to your dropbear.id.au address from 
> home, one of our ISPs apparently has the other blackballed.  I mention 
> this just so you know I'm not intentionally cutting you out of the To: list.

Eck.  That's a pain.

-- 
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