linux-kernel - Re: [PATCH 0/2] make automatic device

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Message-ID: <20150305022714.GG14927@swordfish>
Date:	Thu, 5 Mar 2015 11:27:14 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Nitin Gupta <ngupta@...are.org>, linux-kernel@...r.kernel.org,
	Jerome Marchand <jmarchan@...hat.com>
Subject: Re: [PATCH 0/2] make automatic device_id generation possible

On (03/05/15 11:04), Minchan Kim wrote:
> > we upgraded our scripts but landed some bugs there? it's up to particular
> > implementation. in your example, I assume, someone used zram with num_devices >= 1000?
> > that's impossible. current num_devices limitation is 32. and uid-s start from 1000.
> 
> I meant it.
> If we support use-defined id and someone have used your idea so he can make zram
> per-user as uid. After a while, new application stats automatic id assignment
> so upcoming users can consume upcoming user id. yeah, automaic id will start
> from 0 so it's very rare to reach 1000 but who knows?
> My point is in your usecase, the script would be very fragile so it should
> have second plan like automatic id.

I don't see how it turns any script into a _necessarily fragile_ one
here. there might be buggy scripts, yes. there might be no.

> > these scripts should check if device has been created anyway, it just adds -EEXIST
> > check. in general "what if user space does something wrong" thing can be beaten by
> > "what if user space does everything right" argument. when script fails we just go
> > and fix that script, I guess.
> 
> Yes, I believe finally the script will go automatic id if it was broken.

No, fixing a script does not imply at all switching to automatic device_id
assignment mode.


I think we discuss something that is not quite relevant to zram -- theoretical
ways someone does and fix things, and the policies and mistakes someone come up
with.

let me go and ask guys who asked for on demand device creation if they see
any value in user defined ids or they will be happy with the automatic one.
hopefully they will response in a day or two. can we wait? I'm not really
opposed to the removal of this functionality, but at the same time I see
some benefits.

> So, why does we should support user-defined id if they finally should
> turn around from user-defined to automatic?
> 

	-ss
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