On 2.2.2014, at 13.42, Hannes Reinecke <hare@xxxxxxx> wrote:
[part of explanation snipped from reply]
> But we're now trying to deprecate the original (and unmaintained)
> scsi_id program and replace it with the standard 'sg_inq' program.
> Which is a standard program which just issues the respective SCSI command; most of the post-processing will be done by udev rules.
> And implementing the same workaround here is really a bit hackish.
> Hence this proposal to allow 'sg_inq' (or any program from sg3_utils)
> to be called without interrupting normal operations on a tape device.
>
OK. After your explanation I think adding the new MTIOCTOP operation is the
least ugly solution :-)
>> If you absolutely have to do this, then do it. But new ioctls are deprecated and
>> also it is a bad habit to change the kernel to make things easier for a single
>> program.
>>
> Well, the actual problem here is that the 'st' driver is not designed for multi-initiator environments. The original design for the driver assumed that a single program had control over the 'st' driver, and there is only one instance talking to the hardware.
> Which simply doesn't fit well with the modern, asynchronous, setup.
>
The basic problem is that a sequential access device does not fit well the asynchronous setup. I admit that some simplifications have been made because of this.
> And it's not just udev which suffers here; try to setup multipath on a tape device ...
>
>>> I'll be drafting up a patch.
>>>
>> If you do, don’t forget to update the documentation.
>>
> Okay. New patch attached.
>
I think you have not compiled the patched st.c:
@@ -2263,6 +2265,8 @@ static int st_set_options(struct scsi_tape *STp, long options)
STm->sysv = value;
if ((options & MT_ST_SILI) != 0)
STp->sili = value;
+ if (value && (options & MT_ST_NOREWIND) != 0)
+ Stp->rew_at_close = 0;
^^^
Should be STp.
However, looking at the code already suggests that this operation does not belong to MT_ST_*. These bits set/clear options that persist. The operations you need is transient so that the effect disappears when the device is closed. I think it would be better to define it as and ordinary MTIOCTOP operation code, e.g., in mtio.h:
#define MTNOAUTOREWIND 36 /* suppress possible pending automatic rewind */
or something like that?
Thanks,
Kai
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