Re: [v5 01/12] struct device: Add function callback durable_name

[Hannes Reinecke]

On 10/7/20 10:10 PM, Tony Asleson wrote:
> On 10/1/20 6:48 AM, Greg Kroah-Hartman wrote:
> > On Wed, Sep 30, 2020 at 09:35:52AM -0500, Tony Asleson wrote:
> > > On 9/30/20 2:38 AM, Greg Kroah-Hartman wrote:
> > > > On Tue, Sep 29, 2020 at 05:04:32PM -0500, Tony Asleson wrote:
> > > > > I'm trying to figure out a way to positively identify which storage
> > > > > device an error belongs to over time.
> > > >
> > > > "over time" is not the kernel's responsibility.
> > > >
> > > > This comes up every 5 years or so. The kernel provides you, at runtime,
> > > > a mapping between a hardware device and a "logical" device.  It can
> > > > provide information to userspace about this mapping, but once that
> > > > device goes away, the kernel is free to reuse that logical device again.
> > > >
> > > > If you want to track what logical devices match up to what physical
> > > > device, then do it in userspace, by parsing the log files.
> > >
> > > I don't understand why people think it's acceptable to ask user space to
> > > parse text that is subject to change.
> >
> > What text is changing? The format of of the prefix of dev_*() is well
> > known and has been stable for 15+ years now, right?  What is difficult
> > in parsing it?
>
> Many of the storage layer messages are using printk, not dev_printk.
So that would be the immediate angle of attack ...

> > > > > Thank you for supplying some feedback and asking questions.  I've been
> > > > > asking for suggestions and would very much like to have a discussion on
> > > > > how this issue is best solved.  I'm not attached to what I've provided.
> > > > > I'm just trying to get towards a solution.
> > > >
> > > > Again, solve this in userspace, you have the information there at
> > > > runtime, why not use it?
> > >
> > > We usually don't have the needed information if you remove the
> > > expectation that user space should parse the human readable portion of
> > > the error message.
> >
> > I don't expect that userspace should have to parse any human readable
> > portion, if they don't want to.  But if you do want it to, it is pretty
> > trivial to parse what you have today:
> >
> > 	scsi 2:0:0:0: Direct-Access     Generic  STORAGE DEVICE   1531 PQ: 0 ANSI: 6
> >
> > If you really have a unique identifier, then great, parse it today:
> >
> > 	usb 4-1.3.1: Product: USB3.0 Card Reader
> > 	usb 4-1.3.1: Manufacturer: Generic
> > 	usb 4-1.3.1: SerialNumber: 000000001531
> >
> > What's keeping that from working now?
>
> I believe these examples are using dev_printk.  With dev_printk we don't
> need to parse the text, we can use the meta data.
> So it looks as most of your usecase would be solved by moving to 
dev_printk().
Why not work on that instead?
I do presume this will have immediate benefits for everybody, and will 
have approval from everyone.

Cheers,

Hannes
--
Dr. Hannes Reinecke                Kernel Storage Architect
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