linux-kernel - Re: [PATCH 6/6] overlay: overlay filesystem documentation

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Date:	Tue, 19 Apr 2011 12:05:17 +0900
From:	"J. R. Okajima" <hooanon05@...oo.co.jp>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	viro@...IV.linux.org.uk, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, apw@...onical.com, nbd@...nwrt.org,
	neilb@...e.de, hramrach@...trum.cz,
	Miklos Szeredi <mszeredi@...e.cz>
Subject: Re: [PATCH 6/6] overlay: overlay filesystem documentation


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
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