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

[Daniel P. Berrange]

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:
> >> Add an optional unique_id parameter to nodedev.  Allows for easier lookup
> >> and display of the unique_id value in order to document for use with
> >> scsi_host code.
> >>
> >> Signed-off-by: John Ferlan <jferlan at redhat.com>
> >> ---
> >>  docs/formatnode.html.in                            | 11 +++++++++++
> >>  docs/schemas/nodedev.rng                           |  6 ++++++
> >>  src/conf/node_device_conf.c                        | 23 ++++++++++++++++------
> >>  src/conf/node_device_conf.h                        |  1 +
> >>  src/node_device/node_device_linux_sysfs.c          |  6 ++++++
> >>  src/test/test_driver.c                             |  5 +++--
> >>  .../pci_8086_27c5_scsi_host_0_unique_id.xml        |  8 ++++++++
> >>  tests/nodedevxml2xmltest.c                         |  1 +
> >>  8 files changed, 53 insertions(+), 8 deletions(-)
> >>  create mode 100644 tests/nodedevschemadata/pci_8086_27c5_scsi_host_0_unique_id.xml
> >>
> >> diff --git a/docs/formatnode.html.in b/docs/formatnode.html.in
> >> index 76bf8af..cdf0277 100644
> >> --- a/docs/formatnode.html.in
> >> +++ b/docs/formatnode.html.in
> >> @@ -173,6 +173,17 @@
> >>              <dl>
> >>                <dt><code>host</code></dt>
> >>                <dd>The SCSI host number.</dd>
> >> +              <dt><code>unique_id</code></dt>
> >> +              <dd>On input, this optionally provides the value from the
> >> +                'unique_id' file found in the scsi_host's directory. To
> >> +                view the values of all 'unique_id' files, use <code>find -H
> >> +                /sys/class/scsi_host/host{0..9}/unique_id |
> >> +                xargs grep '[0-9]'</code>. On output, if the unique_id
> >> +                file exists, the value from the file will be displayed.
> >> +                This can be used in order to help uniquely identify the
> >> +                scsi_host adapter in a <a href="formatstorage.html">
> >> +                Storage Pool</a>. <span class="since">Since 1.2.6</span>
> >> +              </dd>
> > 
> > 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 at HansenPartnership.com>
> +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

Regards,
Daniel
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