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Re: [PATCH 01/24] Unionfs: Documentation

From:  Josef Sipek <>
To:  Andrew Morton <>
Subject:  Re: [PATCH 01/24] Unionfs: Documentation
Date:  Mon, 8 Jan 2007 18:25:16 -0500
Cc:  Shaya Potter <>, "Josef 'Jeff' Sipek" <>,,,,,,, David Quigley <>, Erez Zadok <>
Archive-link:  Article, Thread

On Mon, Jan 08, 2007 at 01:19:57PM -0800, Andrew Morton wrote:
> If it's not in the changelog or the documentation, it doesn't exist.

Good point. I'll add it for next time.

> >  It's the same thing as modifying a block 
> > device while a file system is using it.  Now, when unionfs gets confused, 
> > it shouldn't oops, but would one expect ext3 to allow one to modify its 
> > backing store while its using it?
> 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

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.

Josef "Jeff" Sipek.

Computer Science is no more about computers than astronomy is about
		- Edsger Dijkstra
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