Re: /sys/.../enclosure_device:<something> ?

[James Bottomley <James.Bottomley@HansenPartnership.com>]

On Wed, 2016-01-13 at 15:15 -0500, Anne Mulhern wrote:
> 
> 
> 
> ----- Original Message -----
> > From: "James Bottomley" <James.Bottomley@HansenPartnership.com>
> > To: "Anne Mulhern" <amulhern@redhat.com>, 
> > linux-scsi@vger.kernel.org
> > Sent: Wednesday, January 13, 2016 2:15:05 PM
> > Subject: Re: /sys/.../enclosure_device:<something> ?
> > 
> > On Wed, 2016-01-13 at 11:28 -0500, Anne Mulhern wrote:
> > > Hi!
> > > 
> > > I'm looking for the most precise information available about the
> > > meaning of <something>
> > > and from what it is derived. I'm also interested in what the
> > > values
> > > in the files in that directory
> > > may mean. Could somebody point me there?
> > 
> > It's in drivers/misc/enclosure.c:enclosure_link_name()
> > 
> 
> Thanks. I will do my best with that.
> 
> > > Also, how can there be more than one enclosure_device
> > > subdirectory
> > > for the same device,
> > > or, alternatively, why isn't <something> stored in a file in the
> > > more
> > > regularly named directory
> > > /sys/.../enclosure_device?
> > 
> > I'm not sure I parse the question, but if you're asking how can a
> > single enclosure bay appear to have more than one device, that's
> > when
> > there are multiple paths to the device.
> 
> I'm afraid the word path is so overloaded...I'm assuming that you
> are talking about a multipathed environment, where two device nodes, 
> say /dev/sdb, /dev/sdc correspond to the same disk, and are hence
> multipathed. Of course, in that case, it makes sense that both 
> devices should share a bay. And that's what I observe.

Yes, that's what I meant.

> If I understand you correctly, then my question is actually the 
> opposite. Why does it look as if the directories are set up so that 
> there can be multiple bays for a single device...i.e., the directory 
> naming scheme allows me to specify an arbitrary number of bays for 
> /dev/sdb. It seems like there should never be more than one?

There is only one bay per device since a physical disk can't be in more
than one bay at once.  Why do you think it was set up to allow >1?

James

> - mulhern
> 
> > James
> > 
> > > (It would be nice to be able to obtain the value of <something>
> > > using
> > > libudev's attribute
> > > lookup facilities, but making that value a part of the specially
> > > named directory enclosure_device:<something>
> > > makes such a process especially difficult.)
> > > 
> > > Thanks,
> > > 
> > > - mulhern
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