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

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Date:	Mon, 9 Nov 2009 13:28:36 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Thadeu Lima de Souza Cascardo <cascardo@...oscopio.com>
Cc:	linux-kernel@...r.kernel.org, device@...ana.org,
	rubini@...ion.unipv.it, gregkh@...e.de, cluster-devel@...hat.com
Subject: Re: [PATCH] misc: use a proper range for minor number dynamic
 allocation

On Fri, 23 Oct 2009 21:28:17 -0200
Thadeu Lima de Souza Cascardo <cascardo@...oscopio.com> wrote:

> The current dynamic allocation of minor number for misc devices has some
> drawbacks.
> 
> First of all, the range for dynamic numbers include some statically
> allocated numbers. It goes from 63 to 0, and we have numbers in the
> range from 1 to 15 already allocated. Although, it gives priority to the
> higher and not allocated numbers, we may end up in a situation where we
> must reject registering a driver which got a static number because a
> driver got its number with dynamic allocation. Considering fs/dlm/user.c
> allocates as many misc devices as lockspaces are created, and that we
> have more than 50 users around, it's not unreasonable to reach that
> situation.

What is this DLM behaviour of which you speak?  It sounds broken.

> The proposed solution uses the not yet reserved range from 64 to 127. If
> more devices are needed, we may push 64 to 16. Moreover, if we don't
> need to give priority to the higher numbers anymore, we can start using
> the bitmap/bitops functions.

So...  misc minors 64 to 127 are presently unused?

> Finally, if there's a failure creating the device (because there's
> already one with the same name, for example), the current implementation
> does not clear the bit for the allocated minor and that number is lost
> for future allocations.
> 

Is that a bugfix for the existing code?

If so, please split that out into a separate patch which we can review
and apply promptly while we consider the broader problem which you've
identified.


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