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

From: Jerry Van Baren <[email-masked]>
Date: Wed, 18 Apr 2007 08:19:47 -0400

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.

Best regards,
gvb

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.