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

From: Masami Hiramatsu
Date: Thu Jun 16 2011 - 23:33:24 EST

(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 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?

Thank you,

Software Platform Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
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