linux-kernel - How to flush the disk write cache from userspace

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 for Android: free password hash cracker in your pocket

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

Date:	Sun, 14 Jan 2007 04:05:33 +0000
From:	Ricardo Correia <rcorreia@...y.org>
To:	linux-kernel@...r.kernel.org
Subject: How to flush the disk write cache from userspace

Hi, (please CC: to my email address, I'm not subscribed)

Quick question: how can I flush the disk write cache from userspace?

Long question:

I'm porting the Solaris ZFS filesystem to the FUSE/Linux filesystem framework.
This is a copy-on-write, transactional filesystem and so it needs to ensure 
correct ordering of writes when transactions are written to disk.

At the moment, when transactions end, I'm using a fsync() on the block device 
followed by a ioctl(BLKFLSBUF).

This is because, according to the fsync manpage, even after fsync() returns, 
data might still be in the disk write cache, so fsync by itself doesn't 
guarantee data safety on power failure.

I was looking for something like the Solaris ioctl(DKIOCFLUSHWRITECACHE), 
which does exactly what I need.

The most similar thing I could find was ioctl(BLKFLSBUF), however a search for 
BLKFLSBUF on the Linux 2.6.15 source doesn't seem to return anything related 
to IDE or SCSI disks.

Can I trust ioctl(BLKFLSBUF) to flush disks' write caches (for disks that 
follow the specs)?

What about block devices of disk partitions, LVM logical volumes and the EMVS 
volumes, do they propagate flush commands to the respective disks?

What about loop devices?

Thanks in advance.
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/