Date:	Fri, 8 Jul 2011 08:47:36 -0700
From:	Greg KH <greg@...ah.com>
To:	Kay Sievers <kay.sievers@...y.org>
Cc:	Nao Nishijima <nao.nishijima.xt@...achi.com>,
	linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org,
	James.Bottomley@...senpartnership.com, jcm@...hat.com,
	dle-develop@...ts.sourceforge.net,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	yrl.pp-manager.tt@...achi.com, dgilbert@...erlog.com,
	stefanr@...6.in-berlin.de, hare@...e.de
Subject: Re: [RFC PATCH 0/4] Persistent device name using alias name

On Fri, Jul 08, 2011 at 05:41:36PM +0200, Kay Sievers wrote:
> On Fri, Jul 8, 2011 at 16:54, Greg KH <greg@...ah.com> wrote:
> > On Fri, Jul 08, 2011 at 05:45:47PM +0900, Nao Nishijima wrote:
> >> This patch series provides an "alias name" of the disk into kernel and procfs
> >> messages. The user can assign a preferred name to an alias name of the device.
> >>
> >> Based on previous discussion (*), I changed patches as follows
> >> - This is "alias name"
> >> - An "alias name" is stored in gendisk struct
> >> - Add document to Documentation/ABI/testing/sysfs-block
> >> - When the user changes an "alias name", kernel notifies udev
> >>
> >> (*) http://marc.info/?l=linux-scsi&m=130812625531219&w=2
> >
> > I don't like it and I don't think it will really solve the root problem
> > you are trying to address, but as the patches don't touch any code I
> > maintain, there's not much I can do to object to it.
> 
> I can only repeat what I already wrote in detail earlier:
> 
> This approach seems to papers over the problem which emitting and
> parsing free-text printk() messages with much-too-dumb tools cause. It
> seems to fix the symptoms not the cause.
> 
> You can already write a udev rule today that logs _all_ symlinks of a
> device at discovery time, and any later kernel message can safely be
> associated with all possible names of the blockdev. No kernel changes
> needed, all possible names are covered. That also works good enough
> with our current stone-age tools for anybody who is able to scroll
> back to the last log udev message in that same log file.
> 
> There can be by-definition no default udev rules assigning a proper
> single name to a block device. There is never a valid single name for
> a disks, so udev can not ship anything like that in the default setup,
> so this stays as a custom hack.
> 
> We absolutely need _structured_ data for logging and error reporting,
> not only to solve this problem. Along with the current free-text
> printk(), we would be able to attach classifications, device
> error/sense data, firmware register dumps and anything
> interesting-for-debug to the messages.
> 
> We can't solve that problem in the kernel alone. Structured data from
> the kernel will need to feed a smarter userspace logger that can index
> and classify messages, merge current userspace data into it, and
> provides hooks for the system management to act on critical failures
> and raise notifications.
> 
> Structured logging seems like the solution for this and also to many
> other problems in this area. Single custom names pushed into the
> kernel might cover some rather exotic use cases, but I think, is not
> what we are looking for.

I totally agree, but hey, no one listens to us :)

greg k-h
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