From mboxrd@z Thu Jan 1 00:00:00 1970 From: Neil Brown Subject: Re: [PATCH 0/5] hybrid union filesystem prototype Date: Thu, 2 Sep 2010 23:32:00 +1000 Message-ID: <20100902233200.586fcb31@notabene> References: <20100826183340.027591901@szeredi.hu> <20100827170551.19616048@notabene> <20100827213502.31af4a4c@notabene> <20100829144207.4fbf2713@notabene> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Miklos Szeredi , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, vaurora@redhat.com, viro@zeniv.linux.org.uk, jblunck@suse.de, hch@infradead.org To: Jan Engelhardt Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On Thu, 2 Sep 2010 15:15:37 +0200 (CEST) Jan Engelhardt wrote: >=20 > On Monday 2010-08-30 12:18, Miklos Szeredi wrote: > > > >> My comment about set-theory unions being commutative set me thinki= ng. I > >> really don't think "union" is the right name for this thing. Ther= e is > >> nothing about it which really fits that proper definition of a uni= on. > > > >We could call it overlayfs. People learn new names quickly :) >=20 > There is a much larger issue that you should be very well aware about= =C2=A0=E2=80=94 >=20 > "The name wanted to be a clever acronym for "Filesystem in > USErspace", but it turned out to be an unfortunate choice. The author > has since vowed never to name a project after a common term, not even > anything found more than a handful of times on Google." >=20 > overlayfs already exists. Right next to fuse on sourceforge... lol No, I mean it. "Linux Over-Lays". :-) >=20 >=20 > Oh and I what I like to see is support for multiple readonly branches= :) I think we very nearly have that, assuming I understand your requiremen= t correctly. The lower filesystem can itself be an overlay, providing it is mounted read-only. So if /mnt/ro1 /mnt/ro2 /mnt/ro3 are all read-only branches then mount -o ro,lowerdir=3D/mnt/ro1,upperdir=3D/mnt/ro2 meaninglessstring = /mnt/ov1 mount -o ro,lowerdir=3D/mnt/ov1,upperdir=3D/mnt/ro3 meaninglessstring = /mnt/ov2 mount -o lowerdir=3D/mnt/ov2,upperdir=3D/mnt/rw ignoreme /mnt/overlay and /mnt/overlay will be the combination of 3 read-only filesystems and= one writable one. (this doesn't work with the code as-is, but it is really just a few bug= -fixes away). NeilBrown