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Date: Fri, 21 Mar 2014 18:37:07 +0100
From: cinap_lenrek@felloff.net
To: 9front@9front.org
Subject: Re: [9front] prep divide by zero and kernel panic in devfs
In-Reply-To: <20140321065058.GB3145@iota.offblast.org>
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the kernel crash is a off by one bug in error handling codepath
when it tries to clean up state before erroring out:

--- a/sys/src/9/port/devfs.c	Fri Mar 21 16:55:16 2014 +0100
+++ b/sys/src/9/port/devfs.c	Fri Mar 21 18:10:55 2014 +0100
@@ -646,7 +646,7 @@
 Fail:
 		for(i = 1; i < cb->nf; i++)
 			if(idev != nil && idev[i-1] != nil)
-				cclose(idev[i]);
+				cclose(idev[i-1]);
 		if(mp != nil)
 			mdeldev(mp);
 		free(idev);

this has nothing todo with sparsefiles. a sparsefile is a
optimization of the filesystem. it just avoids allocating blocks
containing all zeros, thats all.

you want to use partfs. see the test.disk target in /sys/src/boot/pc/mkfile
devfs is bad because then you need to be hostowner on the machine
and you are manipulating global state to solve a local problem.

--
cinap