Re: [PATCH] vfs: introduce FS_IOC_SYNCFS to sync a single super

[Jonathan Nieder <jrnieder-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

Jonathan Nieder wrote:

> Since
> ancient times, that has been done with the "rename trick":
[...]
> Great.  Problem is, filesystems with delayed allocation like XFS,
> ubifs, ext4, hfs+ don't cope so well with that[1].
[...]
> [1] Yes, even after v2.6.30-rc1~416^2~15 (ext4: Automatically allocate
> delay allocated blocks on rename, 2009-02-23).
> See https://bugzilla.kernel.org/show_bug.cgi?id=18632

Sorry, wrong link.  The example meant was

	https://bugzilla.kernel.org/show_bug.cgi?id=15910

"zero-length files and performance degradation", reported against 2.6.32:

| To reproduce it:
| * install a fresh Ubuntu Lucid system on an ext4 filesystem, or Debian with
| dpkg < 1.15.6 or Ubuntu Karmic
| * install a package, wait a few seconds and simulate a crash 
| $ sudo apt-get install some-package; sleep 5; sudo echo b > /proc/sysrq-trigger
| * reboot
| $ ls -l /var/lib/dpkg/info/some-package.* will list empty maintainer's scripts.
| $ ls -l /var/cache/apt/archive/some-package.* will show the empty archive
| you've just downloaded
| At this stage, the package manager is unusable and the common user cannot
| update anything anymore.
|
| This behavior is observed with data=ordered and with or without the mount
| option auto_da_alloc.

Sorry for the confusion.
Jonathan