linux-kernel - Re: Error testing ext3 on brd ramdisk

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Date:	Thu, 5 Mar 2009 10:46:23 +0100
From:	Nick Piggin <npiggin@...e.de>
To:	"Jorge Boncompte [DTI2]" <jorge@...2.net>
Cc:	ext-adrian.hunter@...ia.com, LKML <linux-kernel@...r.kernel.org>
Subject: Re: Error testing ext3 on brd ramdisk

On Thu, Mar 05, 2009 at 10:19:46AM +0100, Jorge Boncompte [DTI2] wrote:
> Nick Piggin escribió:
> >>------------
> >>mount -no remount,ro /dev/ram0
> >>dd if=/dev/ram0 of=config.bin bs=1k count=1000
> >>mount -no remount,rw /dev/ram0
> >>md5sum config.bin
> >>dd if=config.bin of=/dev/hda1
> >>echo $md5sum | dd of=/dev/hda1 bs=1k seek=1100 count=32
> >>------------
> >>
> >>on system boot
> >>
> >>------------
> >>CHECK MD5SUM
> >>dd if=/dev/hda1 of=/dev/ram0 bs=1k count=1000
> >>fsck.minix -a /dev/ram0
> >>mount -nt minix /dev/ram0 /etc -o rw
> >>------------
> >>
> >>	I have never seen a MD5 failure on boot, just sometimes the 
> >>	filesystem is corrupted. Kernel config attached.
> >
> >>From your description, it suggests that the corrupted image is being
> >read from /dev/ram0 (becuase the md5sum passes).
> 
> 	No, it is read from /dev/hda1.

No I mean when it is first read from /dev/ram0 when you create the
image. Can you put some fsx.minix checks on the image file to try
to narrow down when exactly it is getting corrupted?


> >In your script, can you run fsck.minix on config.bin when you first
> >create it? What if you unmount /dev/ram0 before copying the image?
> 
> 	Yesterday I did some tests and found that doing...
> 
> -----------
> umount /etc (/etc is what is mounted from /dev/ram0)
> dd if=/dev/zero of=/dev/ram0 bs=1k count=1000
> mount /dev/ram0 /etc -t minix -o rw
> -----------
> ...succeds and mounts a corrupted filesystem with the old content. Doing 
> the same with the all ramdisk driver fails on mount with "no filesystem 
> found".
> 
> If I do...
> -----------
> umount /etc (/etc is what is mounted from /dev/ram0)
> echo 3 > /proc/sys/vm/drop_caches
> dd if=/dev/zero of=/dev/ram0 bs=1k count=1000
> mount /dev/ram0 /etc -t minix -o rw
> ----------
> ... then the mount fails with no filesystem found as it should.
> 
> 	Does this ring any bell? :-)

Humph. It seems like a problem with the buffercache layer rather
than brd itself. I'll dig some more.
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