From: NeilBrown <neilb@suse.de>
To: "J. R. Okajima" <hooanon05@yahoo.co.jp>
Cc: Miklos Szeredi <miklos@szeredi.hu>,
viro@ZenIV.linux.org.uk, linux-fsdevel@vger.kernel.org,
linux-kernel@vger.kernel.org, apw@canonical.com, nbd@openwrt.org,
hramrach@centrum.cz, Miklos Szeredi <mszeredi@suse.cz>
Subject: Re: [PATCH 6/6] overlay: overlay filesystem documentation
Date: Tue, 19 Apr 2011 13:58:18 +1000 [thread overview]
Message-ID: <20110419135818.024cd289@notabene.brown> (raw)
In-Reply-To: <7795.1303182317@jrobl>
On Tue, 19 Apr 2011 12:05:17 +0900 "J. R. Okajima" <hooanon05@yahoo.co.jp>
wrote:
>
> Hello Miklos,
>
> Miklos Szeredi:
> > +The lower filesystem can be any filesystem supported by Linux and does
> > +not need to be writable. The lower filesystem can even be another
> > +overlayfs. ...
>
> When user mounts overlayfs over and over like this,
> # mount -t overlayfs -o upper=/rw1,lower=/ro1 none /ovl1
> # mount -t overlayfs -o upper=/rw2,lower=/ovl1 none /ovl2
> :::
> # mount -t overlayfs -o upper=/rwN,lower=/ovl{N-1} none /ovlN
>
> And if he modify a file in the bottom RO layer, then overlayfs copies-up
> the file into each RW layer?
> - 'fileA' exists in only /ro1.
> - nested mounts.
> - run "echo append >> /ovlN/fileA"
> - is fileA copied-up to /rw1, and then to /rw2, and then ... to /rwN?
>
> If user specify a single dir as every upper laery, then the copyup will
> be done only once, or such RW layers are not allowed?
>
>
> J. R. Okajima
Only to top level of an overlay stack is writable. All others are or should
be read only. So only the top level can change.
So in your example, fileA will be copied from ro1 directly into rwN where it
will then be appended to.
NeilBrown
next prev parent reply other threads:[~2011-04-19 3:58 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-04-18 16:00 [PATCH 0/6] overlay filesystem Miklos Szeredi
2011-04-18 16:00 ` [PATCH 1/6] vfs: add i_op->open() Miklos Szeredi
2011-04-18 16:00 ` [PATCH 2/6] vfs: export do_splice_direct() to modules Miklos Szeredi
2011-04-18 16:00 ` [PATCH 3/6] vfs: introduce clone_private_mount() Miklos Szeredi
2011-04-18 16:00 ` [PATCH 4/6] overlay filesystem Miklos Szeredi
2011-04-18 16:00 ` [PATCH 5/6] overlayfs: add statfs support Miklos Szeredi
2011-04-18 16:00 ` [PATCH 6/6] overlay: overlay filesystem documentation Miklos Szeredi
2011-04-19 3:05 ` J. R. Okajima
2011-04-19 3:58 ` NeilBrown [this message]
2011-04-19 4:13 ` J. R. Okajima
2011-04-18 18:19 ` [PATCH 0/6] overlay filesystem Michal Suchanek
2011-04-19 9:39 ` Miklos Szeredi
2011-04-19 9:43 ` [PATCH 1/2] ovl: fix missing include Miklos Szeredi
2011-04-19 9:43 ` [PATCH 2/2] ovl: fix building as a module Miklos Szeredi
2011-05-09 19:14 ` [PATCH 0/6] overlay filesystem Michal Suchanek
2011-05-10 16:30 ` Miklos Szeredi
-- strict thread matches above, loose matches on Subject: below --
2010-09-03 13:41 [PATCH 0/6] overlay filesystem prototype Miklos Szeredi
2010-09-03 13:41 ` [PATCH 6/6] overlay: overlay filesystem documentation Miklos Szeredi
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