From mboxrd@z Thu Jan  1 00:00:00 1970
From: clemens.gruber@pqgruber.com (Clemens Gruber)
Date: Thu, 02 Oct 2014 19:01:01 +0200
Subject: Implementing a driver that listen to a GPIO
Message-ID: <542D84CD.70403@pqgruber.com>
To: kernelnewbies@lists.kernelnewbies.org
List-Id: kernelnewbies.lists.kernelnewbies.org

Hi,

I am just trying to solve a similar problem as Luca described. I have a
TQMa28 board running Linux 3.17-rc7 though.
The capacitors keep the system up for about 1500 more milliseconds after
the power fails. A GPIO line is set to high as soon as the main power is
lost.

So I have not much time to quit an important user space process and to
clean up the ext4 root filesystem before the power fails.

At the moment I pass rootflags=data=journal,commit=1 in the kernel
commandline to lower the risk of data loss.
In the user space application I open important files using the O_SYNC flag.

Is there something else I should do to avoid data loss?

How would you implement the "emergency cleanup on power-failure" logic?
Dedicated driver (similar to the mentioned gpio-event driver?),
implement it with UIO, let a userspace application running as root
select /dev/uioX and cleaning up?

Or should I create a separate partition on my eMMC just for this user
space application data and use a readonly rootfs for the rest?

Thanks for your help!

Best regards,
Clemens