linux-kernel - Re: [PATCH] Chardev checking of overlapping ranges is incorrect.

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Message-ID: <20060807230044.GA4251@austin.ibm.com>
Date:	Mon, 7 Aug 2006 18:00:44 -0500
From:	linas@...tin.ibm.com (Linas Vepstas)
To:	Alan Cox <alan@...rguk.ukuu.org.uk>, rubini@...vis.unipv.it,
	device@...ana.org
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Chardev checking of overlapping ranges is incorrect.

On Mon, Aug 07, 2006 at 05:55:55PM -0500, linas wrote:
> 
> The current code in register_chrdev_region() attempts to check 

A debug printk escaped with that patch. Here's the proper patch.
--linas

[PATCH] Chardev checking of overlapping ranges is incorrect.

The current code in register_chrdev_region() attempts to check 
for overlapping regions of minor device numbers, but performs 
that check incorrectly. For example, if a device with minor 
numbers 128, 129, 130 is registered first, and a device with 
minor number 3,4,5 is registered later, then the later range
is incorrectly identified as "overlapping" (since 130>3), 
when clearly this is the wrong conclusion.

This patch fixes the overlap check to work correctly.

Signed-off-by: Signed-off-by: Linas Vepstas <linas@...tin.ibm.com>

----
 fs/char_dev.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

Index: linux-2.6.18-rc3-mm2/fs/char_dev.c
===================================================================
--- linux-2.6.18-rc3-mm2.orig/fs/char_dev.c	2006-08-07 17:16:53.000000000 -0500
+++ linux-2.6.18-rc3-mm2/fs/char_dev.c	2006-08-07 17:57:51.000000000 -0500
@@ -113,9 +113,13 @@ __register_chrdev_region(unsigned int ma
 		     (((*cp)->baseminor >= baseminor) ||
 		      ((*cp)->baseminor + (*cp)->minorct > baseminor))))
 			break;
+
+	/* Check for overlap of minor ranges */
 	if (*cp && (*cp)->major == major &&
-	    (((*cp)->baseminor < baseminor + minorct) ||
-	     ((*cp)->baseminor + (*cp)->minorct > baseminor))) {
+	    ((((*cp)->baseminor <= baseminor) &&
+		   ((*cp)->baseminor + (*cp)->minorct >= baseminor)) ||
+	     (((*cp)->baseminor >= baseminor) &&
+	      ((*cp)->baseminor <= baseminor+minorct)))) {
 		ret = -EBUSY;
 		goto out;
 	}
-
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