linux-kernel - Re: [PATCH 3/3] misc: use a proper range for minor number dynamic allocation

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Message-ID: <20091216232155.GD7791@holoscopio.com>
Date:	Wed, 16 Dec 2009 21:21:55 -0200
From:	cascardo@...oscopio.com
To:	David Teigland <teigland@...hat.com>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
	rubini@...dd.com, gregkh@...e.de
Subject: Re: [PATCH 3/3] misc: use a proper range for minor number dynamic
 allocation

On Wed, Dec 16, 2009 at 12:01:56PM -0600, David Teigland wrote:
> On Tue, Dec 15, 2009 at 11:37:38PM +0000, Alan Cox wrote:
> > > > I merged this patch, but made a note-to-self that there are remaining
> > > > open issues..
> > > 
> > > And nothing else happened.  Can we revisit this please?
> > 
> > The last I saw was a request for an explanation of the users
> > configuration and how he was getting so many misc devices. Its a bug in
> > dlm if the dlm is doing that but I didn't see any follow up to the DLM
> > folks on the subject from the reporter, so it stays NACKed and conflicts
> > with the device registry.
> 
> I never saw an indication that the dlm ate up all of someone's misc
> devices.  Can we ask the reporter what they were running?
> 

That was not such ocurrence. I don't use DLM. Sorry for all the fuss.
I've simply noticed that DLM was using misc devices to create devices
dynamically after an ioctl. I consider that that ioctl can be called as
many times as I want my userspace program to call, am I right?

> > We need to know from the DLM folks/Thaddeu what is actually going on with
> > that system, especially as it seems to be producing multiple
> > registrations of the same misc device name which is completely broken and
> > should probably be made to error anyway.
> 
> I don't believe the dlm will ever register multiple devices with the same
> name.
> 

No. That was another issue, not related to DLM at all. Again, sorry for
any confusion.

> > Whatever is going on this is the wrong "fix". If DLM should only register
> > it once (as seems the intent) then DLM needs fixing or the users config
> > or both. If it can register many then DLM needs fixing to not eat misc
> > devices.
> 
> I explained here http://lkml.org/lkml/2009/11/9/379 that the dlm does not
> use as many misc devices as has been implied.  It starts with 3, and adds
> one for each *userspace* lockspace.  There are very few applications (I
> know of 3) that create userspace lockspaces, and they each create about
> one each.
> 

The raised issue was that of the device for *each* lock. An application
could request as many as it wanted. If there's no such usecase, I don't
think that's a problem as long as that call is privileged (which may be
easily achieved with the simple chown/chmod).

> That said, I still intend to rework the dlm to use a single device for all
> lockspaces.

That would break current userspace implementations. Or do you have any
idea on solving this without this breakage?

> 
> Dave
> 

Regards and sorry for anything,
Cascardo.
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