Bradley Broom wrote:
>
> On Wed, 21 Mar 2001, Bradley Broom wrote:
> > Summary: My system freezes *completely* when doing an INQUIRY under 2.4.x
> > kernels. SCSI card is a Tekram DC390. Only inquiries to the DISK device cause a
> > hang, others succeed.
>
> This appears to have something to do with tagged queueing on the disk drive.
> If I disable tagged queueing for the disk, everything works fine. Note that
> tagged queueing for the disk works ok when I mount the disk as a filesystem.
>
> However, both cdrecord and scanbus hang when writing an INQUIRY to /dev/sg0
> (the scsi device corresponding to the disk). The system freezes either while
> writing the INQUIRY command or *very* shortly thereafter. The test program I
> wrote never gets so far as to issue the corresponding read.
>
> Obviously, the INQUIRY works when performed by the driver itself; it's just the
> issueing of them via the SG driver that causes problems. I note that the driver
> uses a special subroutine for issueing the INQUIRY command, and this routine
> disables tagged queueing in the DCB. This routine isn't called when the INQUIRY
> command is sent from userland via the SG driver.
The mid-level issues an INQUIRY command during a bus scan.
Bradley,
There is a SCSI_IOCTL_TAGGED_DISABLE ioctl() supported by
the SCSI mid level. So after opening a sg file descriptor
and before sending an INQUIRY, you could try calling this
ioctl().
I am not confident that many adapter drivers take any notice
of the Scsi_Device::tagged_queue flag, but it is worth a try.
It is not obvious why sending a single INQUIRY which returns
up to 256 bytes of data should be affected by the tagged
queue settings. Do TEST UNIT READY commands work?
Doug Gilbert
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