Re: [PATCH] scsi: sr.c use unaligned access helpers

[Boaz Harrosh <bharrosh@panasas.com>]

Jens Axboe wrote:
> On Fri, Oct 03 2008, Harvey Harrison wrote:
>> Preserve the cd->capacity indentation near the #if 0'd if() statement.
>>
>> Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
>> ---
>>  drivers/scsi/sr.c |   26 ++++++++------------------
>>  1 files changed, 8 insertions(+), 18 deletions(-)
>>
>> diff --git a/drivers/scsi/sr.c b/drivers/scsi/sr.c
>> index 27f5bfd..f1b650e 100644
>> --- a/drivers/scsi/sr.c
>> +++ b/drivers/scsi/sr.c
>> @@ -45,6 +45,7 @@
>>  #include <linux/blkdev.h>
>>  #include <linux/mutex.h>
>>  #include <asm/uaccess.h>
>> +#include <asm/unaligned.h>
>>  
>>  #include <scsi/scsi.h>
>>  #include <scsi/scsi_dbg.h>
>> @@ -280,10 +281,7 @@ static int sr_done(struct scsi_cmnd *SCpnt)
>>  		case ILLEGAL_REQUEST:
>>  			if (!(SCpnt->sense_buffer[0] & 0x90))
>>  				break;
>> -			error_sector = (SCpnt->sense_buffer[3] << 24) |
>> -				(SCpnt->sense_buffer[4] << 16) |
>> -				(SCpnt->sense_buffer[5] << 8) |
>> -				SCpnt->sense_buffer[6];
>> +			error_sector = get_unaligned_be32(SCpnt->sense_buffer + 3);
>>  			if (SCpnt->request->bio != NULL)
>>  				block_sectors =
>>  					bio_sectors(SCpnt->request->bio);
>> @@ -445,13 +443,9 @@ static int sr_prep_fn(struct request_queue *q, struct request *rq)
>>  		SCpnt->sdb.length = this_count * s_size;
>>  	}
>>  
>> -	SCpnt->cmnd[2] = (unsigned char) (block >> 24) & 0xff;
>> -	SCpnt->cmnd[3] = (unsigned char) (block >> 16) & 0xff;
>> -	SCpnt->cmnd[4] = (unsigned char) (block >> 8) & 0xff;
>> -	SCpnt->cmnd[5] = (unsigned char) block & 0xff;
>> +	put_unaligned_be32(block, SCpnt->cmnd + 2);
>>  	SCpnt->cmnd[6] = SCpnt->cmnd[9] = 0;
>> -	SCpnt->cmnd[7] = (unsigned char) (this_count >> 8) & 0xff;
>> -	SCpnt->cmnd[8] = (unsigned char) this_count & 0xff;
>> +	put_unaligned_be16(this_count, SCpnt->cmnd + 7);
>>  
>>  	/*
>>  	 * We shouldn't disconnect in the middle of a sector, so with a dumb
> 
> Lets not please, it reduces readability a lot when you are used to SCSI
> cdb filling.
> 
> 

I feel the opposite. That is: put_unaligned_be32(block, SCpnt->cmnd + 2);
is much more readable for me. Coming from the spec, I'm looking for a __b32
at offset CDB+2 and not: "SCpnt->cmnd[4] = (unsigned char) (block >> 8) & 0xff;"
At offset CDB+4 the 2nd-or-3rd? order byte of "block".

And for BE systems it's a gain. So please DO

My $0.017
Boaz