Date: Thu, 12 Jun 2003 15:48:24 -0700
From: Andrew Morton <akpm@digeo.com>
To: Eduardo Pereira Habkost <ehabkost@conectiva.com.br>
Cc: linux-kernel@vger.kernel.org
Subject: Re: Changes made by fdisk not being written to disk (2.5-bk)
Message-Id: <20030612154824.5af9bfde.akpm@digeo.com>
In-Reply-To: <20030612224153.GY4639@duckman.distro.conectiva>
References: <20030612224153.GY4639@duckman.distro.conectiva>
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Eduardo Pereira Habkost <ehabkost@conectiva.com.br> wrote:
>
> Today I changed the partition table of the disk, using fdisk, and
> noticed, after reboot, that the new partition table was not written to
> the disk. Before rebooting, 'fdisk -l /dev/hda' shows the new partition
> table, as if it were written.
> 
> I've made a few more tests, and even if I sync() a dozen of times
> before rebooting (using /bin/sync and sysrq), the data is not written.
> Even when I've waited about 20 minutes after changing the partition table,
> before rebooting, the problem persisted.
> 
> Although, after changing fdisk to call fsync() before closing the device,
> everything worked, the changes were written, and the new partition table
> were on the disk, after rebooting.

argh, is this a plot?

It is some interaction between sync() and the presence of dirty data against
the ramdisk driver.  You can work around it by not using the ramdisk driver,
by using `blockdev --flushbufs /dev/hdXX' or by using fsync, as you have
done.

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