Re: [PATCH 1/3] [RFC] genhd: add a new attribute in device structure

From: Hannes Reinecke
Date: Fri Jun 17 2011 - 02:27:37 EST

On 06/16/2011 07:20 PM, Kay Sievers wrote:
On Thu, Jun 16, 2011 at 19:09, Kay Sievers<kay.sievers@xxxxxxxx> wrote:
On Thu, Jun 16, 2011 at 18:25, James Bottomley
<James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> wrote:
On Thu, 2011-06-16 at 09:14 -0700, Greg KH wrote:
All userspace naming will be taken care of by the usual udev rules, so
for disks, something like /dev/disk/by-preferred/<fred> which would be
the usual symbolic link.

No, udev can not create such a link after the preferred name is set, as
it has no way of knowing that the name was set.

It can if we trigger a uevent. Note: I'm not advocating this ... I'd be
equally happy having whatever sets the kernel name create the link (or
tickle udev to create it). We definitely require device links, though,
to get this to work.

Guess all that would work now, including mount(8) not canonicalizing.
What would happen if we mount:
and some tool later thinks the pretty name should better be 'bar', it
writes the name to /sys, we get a uevent, the old link disappears, we
get a new link, mount has no device node anymore for the mounted
device ...

So we basically get a one-shot additional pretty name? Guess, the
_single_ name changed anytime later just asks for serious problems. We
need to set it very early to be really useful, but how, where is it
coming from?

Well, certain storage arrays are able to print out the user-defined name for the LUNs:

# sg_vpd -p 0xc8 /dev/sdc
Extended device identification (RDAC) VPD Page:
Volume Unique Identifier: 60080e50001bf1f0000005004ddb05a4
Creation Number: 1280, Timestamp: Tue May 24 03:11:00 2011
Volume User Label: mas-1
Storage Array Unique Identifier: 60080e50001bf1f0000000004d418973
Storage Array User Label: LSI-SAS-DIF
Logical Unit Number: 0000000000000000

where the 'Volume User Label' is the name the administrator has given to the LUN on the storage array.

So for these kind of things it would be useful.

However, a single pretty name is quite a limitation.
And I also fail to see why this can't be handled in userspace.


Dr. Hannes Reinecke zSeries & Storage
hare@xxxxxxx +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 NÃrnberg
GF: J. Hawn, J. Guild, F. ImendÃrffer, HRB 16746 (AG NÃrnberg)
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