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SubjectRe: [v5 01/12] struct device: Add function callback durable_name
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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
hare@suse.de +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), Geschäftsführer: Felix Imendörffer

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