linux-kernel - Re: Too large badblocks sysfs file (was: [PATCH v3 0/7] badblocks improvement for multiple bad block ranges)

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Date:   Thu, 23 Sep 2021 15:13:52 +0800
From:   Coly Li <colyli@...e.de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
        linux-raid@...r.kernel.org, nvdimm@...ts.linux.dev,
        antlists@...ngman.org.uk, Dan Williams <dan.j.williams@...el.com>,
        Hannes Reinecke <hare@...e.de>, Jens Axboe <axboe@...nel.dk>,
        NeilBrown <neilb@...e.de>, Richard Fan <richard.fan@...e.com>,
        Vishal L Verma <vishal.l.verma@...el.com>, rafael@...nel.org
Subject: Re: Too large badblocks sysfs file (was: [PATCH v3 0/7] badblocks
 improvement for multiple bad block ranges)

On 9/23/21 2:47 PM, Greg Kroah-Hartman wrote:
> On Thu, Sep 23, 2021 at 02:14:12PM +0800, Coly Li wrote:
>> On 9/23/21 2:08 PM, Greg Kroah-Hartman wrote:
>>> On Thu, Sep 23, 2021 at 01:59:28PM +0800, Coly Li wrote:
>>>> Hi all the kernel gurus, and folks in mailing lists,
>>>>
>>>> This is a question about exporting 4KB+ text information via sysfs
>>>> interface. I need advice on how to handle the problem.
>> Hi Greg,
>>
>> This is the code in mainline kernel for quite long time.
> {sigh}
>
> What tools rely on this?  If none, just don't add new stuff to the file
> and work to create a new api instead.

At least I know mdadm uses this sysfs interface for md raid component 
disks monitoring. It has been in mdadm for around 5 years.

Yes you are right, let it be for existing sysfs interface to avoid 
breaking things.

>>> Please do not do that.  Seriously, that is not what sysfs is for, and is
>>> an abuse of it.
>>>
>>> sysfs is for "one value per file" and should never even get close to a
>>> 4kb limit.  If it does, you are doing something really really wrong and
>>> should just remove that sysfs file from the system and redesign your
>>> api.
>> I understand this. And what I addressed is the problem I need to fix.
>>
>> The code is there for almost 10 years, I just find it during my work on bad
>> blocks API fixing.
>>
>>
>>>> Recently I work on the bad blocks API (block/badblocks.c) improvement, there
>>>> is a sysfs file to export the bad block ranges for me raid. E.g for a md
>>>> raid1 device, file
>>>>       /sys/block/md0/md/rd0/bad_blocks
>>>> may contain the following text content,
>>>>       64 32
>>>>      128 8
>>> Ick, again, that's not ok at all.  sysfs files should never have to be
>>> parsed like this.
>> I cannot agree more with you. What I am asking for was ---- how to fix it ?
> Best solution, come up with a new api.
>
> Worst solution, you are stuck with the existing file and I can show you
> the "way out" of dealing with files larger than 4kb in sysfs that a
> number of other apis are being forced to do as they grow over time.

Now I am sure you are very probably not willing to accept the patches, 
even I know how to do that :-)

>
> But ideally, just drop ths api and make a new one please.

OK, then I leave the existing things as what they are, avoid to make 
them worse.

Thanks for your response.

Coly Li