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

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Date:	Thu, 16 Jun 2011 09:14:42 -0700
From:	Greg KH <greg@...ah.com>
To:	James Bottomley <James.Bottomley@...senPartnership.com>
Cc:	Nao Nishijima <nao.nishijima.xt@...achi.com>,
	linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
	kay.sievers@...y.org, jcm@...hat.com, hare@...e.de,
	stefanr@...6.in-berlin.de, yrl.pp-manager.tt@...achi.com
Subject: Re: [PATCH 1/3] [RFC] genhd: add a new attribute in device structure

On Thu, Jun 16, 2011 at 11:50:54AM -0400, James Bottomley wrote:
> > And again, why not just fix the userspace tools?  That is trivial to do
> > so and again, could have been done by now in the years this has been
> > discussed.
> 
> So I can summarise where I think we are in these discussions:
> 
> We provide the ability to give all kernel devices a "preferred name".
> By default this will be the device name the kernel would have originally
> assigned.  the dev_printk's will use the preferred name, and it will be
> modifiable from user space.  All the kernel will do is print out
> whatever it is ... no guarantees of uniqueness or specific format will
> be made.  Since we're only providing one preferred_name file, the kernel
> can only have one preferred name for a device at any given time
> (although it is modifiable on the fly as many times as the user
> chooses).
> 
> The design is to use this preferred name to implement what Hitachi wants
> in terms of persistent name, but we don't really care.
> 
> 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.

> This will ensure that kernel output and udev input are consistent.  It
> will still require that user space utilities which derive a name for a
> device will need modifying to print out the preferred name.

It also doesn't solve the issue of userspace wanting to use such a
"preferred" name in the command line of tools, as there will not be a
link back to the "kernel" name directly in /dev/.

So as userspace tools will still need to be fixed, I don't see how
adding a kernel file for this is going to help any.  Well, a bit in that
the kernel log files will look "different", but again, that really isn't
a problem that userspace couldn't also solve with no kernel changes
needed.

thanks,

greg k-h
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