From mboxrd@z Thu Jan  1 00:00:00 1970
From: Michael Heimpold <mhei@heimpold.de>
Date: Tue, 21 May 2013 19:34:06 +0200
Subject: [U-Boot] [PATCH] tools/fw_env: use fsync to ensure that data is
	physically stored
In-Reply-To: <20130521124723.D2F42384809@gemini.denx.de>
References: <1369078482-5863-1-git-send-email-mhei@heimpold.de>
	<20130521124723.D2F42384809@gemini.denx.de>
Message-ID: <456389491.x65y6Gi2JO@kerker>
List-Id: <u-boot.lists.denx.de>
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
To: u-boot@lists.denx.de

Hi Wolfgang Denx,

> > Closing a file descriptor does not guarantee that the data has been
> > successfully saved to disk, as the kernel might defer the write.
> 
> What is the exact problem you are trying to fix?
> 
> I mean, when exactly does adding the sync play a role?

I'm using fw_setenv during system update process. The sequence
of such a shell script is something like (much simplified):

...
fw_setenv state=2
dd if=... of=/dev/mmcblk0...
fw_setenv state=1
...
reboot

The (redundant) environment is stored in a eMMC flash.
The env var 'state' gives a hint to U-Boot whether/where the process
was interrupted.

So my intension is to be absolutely sure, that when fw_setenv returns,
the environment is written out to disk.

Best regards,
Michael