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

[Nao Nishijima <nao.nishijima.xt@hitachi.com>]

Hi Kay,

Thank you for looking at it.

(2011/06/17 2:20), Kay Sievers wrote:
> On Thu, Jun 16, 2011 at 19:09, Kay Sievers <kay.sievers@vrfy.org> wrote:
>> On Thu, Jun 16, 2011 at 18:25, James Bottomley
>> <James.Bottomley@hansenpartnership.com> 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:
>   /dev/disk/by-pretty/foo
> 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?
> 

If we can avoid serious problems, I will implement preferred name as
write once.

I have two idea for work preferred name from the very first steps during
early boot in initramfs.

1. I think we can provide udev rules for preferred name in initramfs.
2. (option) I consider using user-defined name for the LUNs(*) because
   it is possible to get the name in initramfs. The user store preferred
   name in LUNs by sg command if available.

(*) Hannes say:
> 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. 


Thanks,

-- 
Nao NISHIJIMA
Software Platform Research Dept. Linux Technology Center
Hitachi, Ltd., YOKOHAMA Research  Laboratory
Email： nao.nishijima.xt@hitachi.com