Re: [PATCH] 2.6.2-rc2 - MPT Fusion driver 3.00.02 update

[Douglas Gilbert <dougg@torque.net>]

James Bottomley wrote:
> On Mon, 2004-01-26 at 11:01, Moore, Eric Dean wrote:
> 
>>I will work on that.  
> 
> 
> Thanks.
> 
> 
>>I had avoided it due the comments in the code
>>from sralston and pdelaney about sg interface 
>>gererating wrong direction in some cases.  
> 
> 
> If you find a problem, I'll fix the generic code...

James,
The newer sg_io_hdr based code (as used by the SG_IO ioctl)
requires that the user explicitly define the data direction
if any data transfer is involved. There is however a
SG_DXFER_UNKNOWN which maps to SCSI_DATA_UNKNOWN which
maps to DMA_BIDIRECTIONAL **.

The older sg_header based code (and the SCSI_IOCTL_SEND_COMMAND
ioctl) deduced the direction from various data buffer lengths
provided by the user. If those length implied both read and write
then the data direction is set as "FROM_DEVICE" (i.e. read
dominates).

So the sg (or SG_IO/SCSI_IOCTL_SEND_COMMAND ioctl) user controls
the data direction and they are free to get it wrong:-)


** The Object Storage Device (OSD) commands use bidirectional
data transfers so perhaps we should think about catering for
that.

Doug Gilbert