Re: [PATCH] scsi: fix scsi_get_lba helper function for pc command

[James Bottomley <James.Bottomley@suse.de>]

On Wed, 2010-06-02 at 16:33 +0900, FUJITA Tomonori wrote:
> This fixes scsi_get_lba() helper function for PC commands.
> 
> Only the block layer is supposed to touch rq->__sector. We could
> create a new accessor for it. But it seems overdoing a bit? Jens?
> 
> =
> From: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
> Subject: [PATCH] scsi: fix scsi_get_lba helper function for pc command
> 
> scsi_get_lba() can be used to get the lba info from
> scsi_cmnd. scsi_get_lba() gets the lba info from rq->__sector so
> scsi_get_lba() returns a bogus value for PC commands (we don't use
> rq->__sector for PC commands).
> 
> This patch sets rq->__sector in scsi_setup_blk_pc_cmnd() so that
> scsi_get_lba() works with PC commands.
> 
> scsi_get_data_transfer_info() is taken from
> scsi_debug. scsi_get_data_transfer_info() looks useful for some
> (scsi_debug, scsi_trace, libata, etc). So I export it. I'll convert
> them to use scsi_get_data_transfer_info().
> 
> Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
> ---
>  drivers/scsi/scsi_lib.c  |   54 +++++++++++++++++++++++++++++++++++++++++++++-
>  include/scsi/scsi_cmnd.h |    4 +++
>  2 files changed, 57 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> index 1646fe7..b9b7f40 100644
> --- a/drivers/scsi/scsi_lib.c
> +++ b/drivers/scsi/scsi_lib.c
> @@ -19,6 +19,7 @@
>  #include <linux/delay.h>
>  #include <linux/hardirq.h>
>  #include <linux/scatterlist.h>
> +#include <asm/unaligned.h>
>  
>  #include <scsi/scsi.h>
>  #include <scsi/scsi_cmnd.h>
> @@ -69,6 +70,52 @@ struct kmem_cache *scsi_sdb_cache;
>  
>  static void scsi_run_queue(struct request_queue *q);
>  
> +int scsi_get_data_transfer_info(unsigned char *cmd, unsigned long long *lba,
> +				unsigned int *num, unsigned int *ei_lba)
> +{
> +	int ret = 0;
> +
> +	switch (*cmd) {
> +	case VARIABLE_LENGTH_CMD:
> +		*lba = get_unaligned_be64(&cmd[12]);
> +		*num = get_unaligned_be32(&cmd[28]);
> +		*ei_lba = get_unaligned_be32(&cmd[20]);
> +		break;

You can't do this ... unless you know the format of the command.  For
instance, if you knew this was a 32 byte CDB, then SPC does define where
the LBA is.

> +	case WRITE_16:
> +	case READ_16:
> +	case VERIFY_16:
> +	case WRITE_SAME_16:
> +		*lba = get_unaligned_be64(&cmd[2]);
> +		*num = get_unaligned_be32(&cmd[10]);
> +		break;
> +	case WRITE_12:
> +	case READ_12:
> +	case VERIFY_12:
> +		*lba = get_unaligned_be32(&cmd[2]);
> +		*num = get_unaligned_be32(&cmd[6]);
> +		break;
> +	case WRITE_10:
> +	case READ_10:
> +	case XDWRITEREAD_10:
> +	case VERIFY:
> +	case WRITE_SAME:
> +		*lba = get_unaligned_be32(&cmd[2]);
> +		*num = get_unaligned_be16(&cmd[7]);
> +		break;
> +	case WRITE_6:
> +	case READ_6:
> +		*lba = (u32)cmd[3] | (u32)cmd[2] << 8 |
> +			(u32)(cmd[1] & 0x1f) << 16;
> +		*num = (0 == cmd[4]) ? 256 : cmd[4];
> +		break;

I really wouldn't do it like this because there are going to be
unexpected gaps.  What about using the CDB groups instead?  Each CDB
group has a well defined location for the LBA.  The only problem is the
16 byte commands group because they have two forms: ordinary and long
LBA.

James