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SubjectRe: [PATCH 01/24] Unionfs: Documentation
On Tue, Jan 09, 2007 at 09:49:35AM +0000, Christoph Hellwig wrote:
> On Mon, Jan 08, 2007 at 06:25:16PM -0500, Josef Sipek wrote:
> > > There's no such problem with bind mounts. It's surprising to see such a
> > > restriction with union mounts.
> > Bind mounts are a purely VFS level construct. Unionfs is, as the name
> > implies, a filesystem. Last year at OLS, it seemed that a lot of people
> > agreed that unioning is neither purely a fs construct, nor purely a vfs
> > construct.
> >
> > I'm using Unionfs (and ecryptfs) as guinea pigs to make linux fs stacking
> > friendly - a topic to be discussed at LSF in about a month.
>
> And unionfs is the wrong thing do use for this. Unioning is a complex
> namespace operation and needs to be implemented in the VFS or at least
> needs a lot of help from the VFS. Getting namespace cache coherency
> and especially locking right is imposisble with out that.

What I meant was that I use them as an example for a linear and fanout
stacking examples. While unioning itself is a complex operation, the general
idea of one set of vfs objects (dentry, inode, etc.) pointing to several
lower ones is very generic and applies to all fan-out stackable fs.

Josef "Jeff" Sipek.

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