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

From: Kay Sievers
Date: Sat Jun 18 2011 - 15:55:44 EST

On Sat, Jun 18, 2011 at 21:40, James Bottomley
<James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> wrote:
> On Fri, 2011-06-17 at 09:22 -0700, Greg KH wrote:
>> On Fri, Jun 17, 2011 at 06:12:14PM +0200, Kay Sievers wrote:
>> > On Fri, Jun 17, 2011 at 17:39, Kay Sievers <kay.sievers@xxxxxxxx> wrote:
>> > > On Fri, Jun 17, 2011 at 16:49, James Bottomley
>> >
>> > >> So this is subsystem specific. ÂFor the case of a SCSI enclosure, I can
>> > >> answer that it's actually burned into the enclosure firmware. ÂWhen you
>> > >> build an enclosure with labels, the label names are stored in a
>> > >> diagnostic page. ÂWe can actually interrogate the enclosure directly or
>> > >> use the ses driver to get these names mapped to current devices.
>> > >
>> > > To me this sounds like a nice name on top of the current bunch of
>> > > names, not like a 'preferred' name.
>> > >
>> > > I still don't like to introduce any new facility to the kernel that
>> > > can handle only one single name. Reality the last years has taught us
>> > > a very different story, and we've walked a long way to get where we
>> > > are. I really don't believe single names will ever work, it's just a
>> > > nice theory.
>> >
>> > I might need to clarify this a bit.
>> >
>> > I have no problem in general to add a 'alias' to every disk, and use
>> > that when stuff is logged. Just the same way the netifs have an alias.
>> > Sure, it might be useful for some use cases. And if that helps to
>> > solve any real problem, we should just do it.
>> >
>> > I just want to make clear, that I don't think that it is anywhere near
>> > to a solution for the problems which are described here. And that
>> > nobody should see this as an excuse not to get their stuff together
>> > and work on the problem, which is that we don't have machine-readable
>> > error and debug from the kernel and a smart syslog.
>> >
>> > If we had that, I'm very sure nobody would even ask for a 'pretty
>> > name' in the kernel, and I think that is a good indication that we are
>> > not on the right track here.
>> And I totally agree here, which is why I don't want to accept this
>> change to the driver core to add this, as it's not the correct solution.
> OK, fine ... we'll do it as gendisk only then. ÂI suppose that is the
> 95% use case anyway.

Sounds fine. It's probably easier to have it domain-specific anyway.
Just like the netif alias already is.

I would suggest not to call it 'preferred' though, but something
similar to 'alias'. Having /dev/disk/by-preferred/ doesn't sound too
convincing to me.

An 'change' uevent when the alias is set sounds fine. I don't think a
set-once policy is needed.

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