linux-kernel - Re: [ANNOUNCE] Btrfs: a copy on write, snapshotting FS

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Date:	Thu, 14 Jun 2007 02:59:23 -0400
From:	"Albert Cahalan" <acahalan@...il.com>
To:	"Chris Mason" <chris.mason@...cle.com>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	hch@...radead.org, snitzer@...il.com
Subject: Re: [ANNOUNCE] Btrfs: a copy on write, snapshotting FS

On 6/13/07, Chris Mason <chris.mason@...cle.com> wrote:
> On Wed, Jun 13, 2007 at 12:14:40PM -0400, Albert Cahalan wrote:
> > On 6/13/07, Chris Mason <chris.mason@...cle.com> wrote:
> > >On Wed, Jun 13, 2007 at 01:45:28AM -0400, Albert Cahalan wrote:

> > >> * secure delete via destruction of per-file or per-block random crypto
> > >keys
> > >
> > >I'd rather keep secure delete as a userland problem (or a layered FS
> > >problem).  When you take backups and other copies of the file into
> > >account, it's a bigger problem than btrfs wants to tackle right now.
> >
> > It can't be a userland problem if you allow disk blocks to move.
> > Volume resizing, logging/journalling, etc. -- they combine to make
> > the userland solution essentially impossible. (one could wipe the
> > whole partition, or maybe fill ALL space on the volume)
>
> Right about here is where I would insert a long story about ecryptfs, or
> encryption solutions that happen all in userland.  At any rate, it is
> outside the scope of v1.0, even though I definitely agree it is an
> important problem for some people.

I'm sure you do have a nice long story, and I'm sure it seems
correct, but there is something not quite right about the add-on
hacks.

BTW, I'm suggesting that this be about deletion, not protection
of data you wish to keep. It covers more than just file bodies.
It covers inode data, block allocations, etc.

> > >> * atomic creation of copy-on-write directory trees
> > >
> > >Do you mean something more fine grained than the current snapshotting
> > >system?
> >
> > I believe so. Example: I have a linux-2.6 directory. It's not
> > a mount point or anything special like that. I want to copy
> > it to a new directory called wip, without actually copying
> > all the blocks. To all the normal POSIX API stuff, this copy
> > should look like the result of "cp -a", not hard links.
>
> This would be a snapshot, which has to be done on a subvolume right now.
> It is not as nice as being able to pick a random directory, but I've
> only been able to get this far by limiting the feature scope
> significantly.  What I did do was make subvolumes very cheap...just make
> a bunch of them.

Can a regular user create and use a subvolume? If not, then
this doesn't work. (if so, then I have other concerns...)
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