linux-ext4 - Writing one file, observing two writes

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <534AB1F3.2060700@seceng.informatik.tu-darmstadt.de>
Date:	Sun, 13 Apr 2014 11:49:07 -0400
From:	Sebastian Biedermann 
	<biedermann@...eng.informatik.tu-darmstadt.de>
To:	linux-ext4@...r.kernel.org
Subject: Writing one file, observing two writes

Dear ext4 developers,

I'm working on a research project about side channel attacks to hard drives.
My testbed runs Ubuntu Linux 12.04 with ext4 file system.

When writing a random file with dd command to my hard drive, I could see
the process jbd2/sda1
writing two times while it seems to wait a fixed period of time between
these two writes.

I actually think that the process is first writing the data to the
sectors and then updating the ext4 data base in a second step.
Is that true or am I wrong? Why is it waiting some seconds between these
two steps and on what is that delay depending?

Thank you!
Sebastian
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html