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

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?

Quoted 9 lines · Lan Tran

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

Thanks Patrick for the tip! After trying out SG_IO, it works, as long as we use Mike C's patch.

Lan

Quoted 30 lines · Patrick Mansfield

Quoted 9 lines · Lan Tran

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.