linux-ext4 - Re: [PATCH e2fsprogs] Add ZFS detection to libblkid

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Date:	Mon, 13 Apr 2009 20:29:22 +0100
From:	"Ricardo M. Correia" <Ricardo.M.Correia@....COM>
To:	Andreas Dilger <adilger@....COM>
Cc:	Eric Sandeen <sandeen@...hat.com>, "Theodore Ts'o" <tytso@....edu>,
	linux-ext4@...r.kernel.org, Karel Zak <kzak@...hat.com>
Subject: Re: [PATCH e2fsprogs] Add ZFS detection to libblkid

On Ter, 2009-04-07 at 00:40 -0700, Andreas Dilger wrote:
> > However, even though currently it's txg nr 4 that gets written first,
> > this is an implementation-specific detail that we cannot (or should not)
> > rely upon.
> 
> So my proposal to check the 0th, 4th, and 8th überblock in both
> the first and second VDEV label should be pretty safe.

Yes, that should be relatively safe :)

Where should I be sending patches for this? e2fsprogs, util-linux-ng,
libvolume_id in udev, ... all of them?

> > If this is not done, then maybe leaving the ZFS labels intact could be
> > better, so that the user has a chance to recover (some/most) of it's
> > data, in case he made a mistake.
> 
> Well, if ZFS is currently using this filesystem, then the kernel will
> have the block device open O_EXCL, which will prevent the mkfs from
> happening.

Not if the pool is exported :)

> Whether it will be a feature to "--force" mkfs to overwrite an ext3
> superblock or ZFS superblock is questionable.  The problem with needing
> "--force" is that people tend to hard-code this into their scripts
> (so that their script always works) and then due to only having a single
> "--force" flag it also forces other, possibly more destructive, behaviour
> (e.g. --force is needed to mke2fs on a file so that it can be mounted
> via loopback, but will also force mke2fs on a filesystem that actually
> IS in use, etc).

What about '--force-overwrite' or something similar?

It wasn't scripts that I was so concerned about. I think this filesystem
detection would be more useful when running mkfs in a shell, where it is
more likely for the user to make mistakes (e.g. mistype /dev/sdd1
as /dev/sde1 or /dev/sda1 as /dev/sda2).

Thanks,
Ricardo

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