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

[Coly Li]

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