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

From: Greg KH
Date: Fri Jun 17 2011 - 01:26:51 EST

On Fri, Jun 17, 2011 at 12:33:05PM +0900, Masami Hiramatsu wrote:
> (2011/06/17 1:14), Greg KH wrote:
> > 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/.
> Right, this series just add a preferred name interface, and changes
> a part of kernel messages.

So, just a tiny part of what you want to do in the end?

> > 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.
> hmm, He didnt say "this can solve all problems". I think
> preferred name is just a starting point to solve these problems.
> Actually, he decided to fix those user space tools to accept
> persistent symbolic links, and to show it in outputs.
> It's not complete, but a good starting point, isn't it?

A starting point for what? What is your "end goal" here to accomplish?

As this does not seem to me to really solve what you see as your "real"
problem, perhaps you can explain what your next steps are going to be
after this?


greg k-h
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