Re: [libvirt] [PATCH 6/8] Add unique_id to nodedev output

On Wed, Jun 11, 2014 at 10:00:24AM -0400, John Ferlan wrote: > > > On 06/11/2014 05:31 AM, Daniel P. Berrange wrote: >> On Tue, Jun 10, 2014 at 03:03:55PM -0400, John Ferlan wrote: >> >> Where is the data from the 'unique_id' coming from ? Is this since that >> Linux makes up, or is it some standard attribute from the hardware ? It >> would be desirable to document what it is in a way that's not simply >> refering to Linux sysfs, since sysfs itself is mostly undocumented :-) >> >> > > Using 'unique_id' was from Osier's initial design - I 'assumed' that his > research into this had determined using this was unique enough. > > A small amount of searching turns this up: > > https://lkml.org/lkml/2011/8/17/274 > ... > +What: /sys/bus/scsi/devices/host*/scsi_host/host*/unique_id > +Date: February, 2003 > +KernelVersion: Unknown > +Contact: James Bottomley <James.Bottomley(a)HansenPartnership.com&gt; > +Description: > + Read only unsigned integer uniquely identifying the SCSI host > + within the system. This value is assigned by the low level > + driver. > + > ... > > > Also from various sources, there's '/linux/include/scsi/scsi_host.h > > /* > * This is a unique identifier that must be assigned so that we > * have some way of identifying each detected host adapter properly > * and uniquely. For hosts that do not support more than one card > * in the system at one time, this does not need to be set. It is > * initialized to 0 in scsi_register. > */ > unsigned int unique_id; Hmm, that's all rather fuzzy. I wonder how much "better" this is unique int ID is than the current hostNN numbers. eg is this unique id stable when you plug / unplug iSCSI targets in arbitrary order