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

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Date:	Thu, 5 Mar 2015 13:10:10 +0100
From:	Karel Zak <kzak@...hat.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 Thu, Mar 05, 2015 at 11:04:36AM +0900, Minchan Kim wrote:
> On Thu, Mar 05, 2015 at 10:47:52AM +0900, Sergey Senozhatsky wrote:
> > On (03/05/15 10:33), Minchan Kim wrote:
> > > > hm, I can think of a huge build server with tons of users. /dev/zram$(id -u)
> > > > created during user login and destroyed during logout. so users use theirs own
> > > > zram devices with predictable device ids (which also makes it simpler for admin)
> > > > for compilation/etc., and don't pressure hdds that much.
> > > 
> > > They upgraded the system and from now on, one of app tries automatic
> > > id with zram for some reason. What happens if he gets some user id
> > > before the user login? The system should have fallback in the case of
> > > failing to create own userid assignment.
> > 
> > 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?

Why 1000?  

The UID_MIN and UID_MAX is nothing strictly defined, it's just option
in /etc/login.defs. I guess it's nothing unusually to have system
where UID_MIN is 500 :-)

    Karel


-- 
 Karel Zak  <kzak@...hat.com>
 http://karelzak.blogspot.com
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