Re: extracting infos from struct scsi_cmnd

[Jens Axboe <axboe@suse.de>]

On Sat, Nov 27 2004, Tommaso Moroni wrote:
> Hi!
> 
> I'm writing a module for the 2.6.9 kernel which tracks accesses on a
> usb-storage device; in particular I'm interested in extracting from a
> struct scsi_cmnd the data read/written and the associated sector. 
> 
> 
> The code I'vr written till now looks like the following:
> 
> 
> struct scsi_cmnd * cmd;
> [...]
> if (cmd->use_sg == 0)
> {
> 	buf = cmd->buffer;
> 	buflen = cmd->bufflen;
> 	sector = cmd->request->sector;

->request_bufflen and ->request_buffer.

> } else {
> 	struct scatterlist * sl = (struct scatterlist *) cmd->buffer;
> 	for (i = 0; i < cmd->use_sg; i++)
> 	{
> 		buf = page_address(sl[i].page) + sl[i].offset;
>                 buflen = sl[i].length;
> 		/* sector? */
> 	}
> }

This only works on non-highmem pages, you should use kmap/kmap_atomic
instead.

> Is it correct?
> Where can I find the sector involved in the operation if the
> scatter-gather is used?

It's ->request->sector as well. The total length is just the sum of the
sg elements.

-- 
Jens Axboe