letting glabel recognise a media change

[Pawel Jakub Dawidek]

On Thu, Sep 30, 2010 at 08:46:11PM +0300, Alexander Motin wrote:
> Andriy Gapon wrote:
> > on 30/09/2010 01:28 Matthew Jacob said the following:
> >> If something like that was in place, I assure you that things would start to use
> >> it very quickly.
> > 
> > I am not sure about this.
> > Because, e.g. I don't see an easy way to know that media is changed in scsi_cd
> > driver.  That is, without polling.  I don't consider polling to be an easy way for
> > a number of reasons.
> 
> SATA specification defines concept of Asynchronous Notification. It is
> already used by port multipliers to report about PHY events. It is also
> supposed to be used by CD drives to report media change. I haven't seen
> such devices yet, but hope they may appear sometimes.
> 
> And even without AN support it would be nice to implement proper
> handling for SCSI "UA - media changed" errors within CAM. It still won't
> be perfect without using polling, but probably still something.

I'd like to know the original reason why CD device is represented by
GEOM provider and not CD media. For my naive thinking CD media should be
GEOM provider that we taste once the media is inserted and orphan once
the media is removed. I don't see any reasons for CD device to be useful
GEOM provider, but maybe I'm overlooking something.

Poul-Henning or Soren, do you remember who made and why this design choice?

-- 
Pawel Jakub Dawidek                       http://www.wheelsystems.com
pjd at FreeBSD.org                           http://www.FreeBSD.org
FreeBSD committer                         Am I Evil? Yes, I Am!
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