Re: BUG: SCSI INQUIRY thru SCSI_IOCTL_SEND_COMMAND returns no errno for disconnected device

[Patrick Mansfield <patmans@us.ibm.com>]

On Thu, Sep 30, 2004 at 12:43:47PM -0700, Lan Tran wrote:
> We have a SAN system set up, where our host is connected to IBM ESS
> storage and SVC storage. When we disconnect ALL FC cables between the
> host and storage devices, and then send a SCSI INQUIRY using the
> SCSI_IOCTL_SEND_COMMAND ioctl to the
> sd devices, the ioctl does not return with a failure code. Instead, it
> returns with a zero-length buffer.
> 
> Is there a reason why we would get a zeroed-length buffer instead of
> an error return code?

SCSI_IOCTL_SEND_COMMAND is deprecated, you should be using SG_IO instead.

There was a bug with SG_IO, it does not correctly set all of the status
bytes, a patch has been submitted a few times, Mike C's patch
fixed problems compared to ones I posted earlier, this patch:

	http://marc.theaimsgroup.com/?l=linux-scsi&m=108617935710955&w=2

It looks like SCSI_IOCTL_SEND_COMMAND has a similiar issue, in that it
only checks the low byte of the results, so for example a DID_NO_CONNECT
returned by the qlogic or emulex driver would be ignored.

See drivers/block/scsi_ioctl.c near the end of sg_scsi_ioctl, this:

	err = rq->errors & 0xff;        /* only 8 bit SCSI status */

Compare that to code in drivers/scsi/scsi_ioctl.c near the end of
scsi_ioctl_send_command, where the entire result is checked, not just the
SCSI byte.

-- Patrick Mansfield