[Info-vax] Alerting on tape insert

[Stephen Hoffman]

On 2012-10-09 23:35:03 +0000, Rich Jordan said:

> Does a SCSI attached tape drive send any kind of notification to VMS
> (ignored by default or not) when a tape is loaded into the drive, if
> the drive is currently unallocated and not being waited on by any
> program?

The SCSI device doesn't know from its allocation status, etc.

> I'm just wondering if there's a way to trip an event to have
> a program check that media for various characteristics (write enabled,
> label, etc)

Polling.  Or hold an I/O channel to the device, and ask the drive.

> I can poll (using a program that issues a QIO with IO$_PACKACK) to see
> if the media is present/loaded (and then doing whatever else is needed
> to verify its writable status) but I'm wondering if there's a way for
> VMS to let me know a tape has been loaded in a specific drive without
> polling.

VMS doesn't include a notification mechanism.

> I suppose I could leave a program that issues a mount to the drive and
> just 'waits' for a tape to show up but that seems inelegant.

If you're writing an app, there are SCSI-level notifications available 
from various drives.  VMS doesn't use them, but the command packet 
interface does allow an application to request them from a SCSI device. 
 But that means the drive is going to have an application I/O channel, 
and some other baggage.

And if you're tossing SCSI-level commands at the SCSI device, it 
doesn't need to be mounted.

Dig up the T10 SCSI specs and start reading.  I don't remember off-hand 
if the notification sequence is in the base SCSI commands 
documentation, or in the block device commands.  But I think it's in 
the latter.


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