From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mailgw-02.dd24.net ([193.46.215.43]:49447 "EHLO mailgw-02.dd24.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752045AbbLLU2D (ORCPT ); Sat, 12 Dec 2015 15:28:03 -0500 Message-ID: <1449952078.6742.10.camel@scientia.net> Subject: Re: subvols, ro- and bind mounts - how? From: Christoph Anton Mitterer To: Chris Murphy , "S.J." Cc: Btrfs BTRFS Date: Sat, 12 Dec 2015 21:27:58 +0100 In-Reply-To: References: <1448340960.14125.51.camel@scientia.net> <1448400350.21291.88.camel@scientia.net> <1449635882.20578.2.camel@scientia.net> <1449782004.7032.19.camel@scientia.net> <5669FE64.2090308@anonym.com> Content-Type: multipart/signed; micalg="sha-512"; protocol="application/x-pkcs7-signature"; boundary="=-g25rICPu3S5CI3rq43iT" Mime-Version: 1.0 Sender: linux-btrfs-owner@vger.kernel.org List-ID: --=-g25rICPu3S5CI3rq43iT Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Thu, 2015-12-10 at 19:32 -0700, Chris Murphy wrote: > That seems due for a revision because I do rw, ro, rw, rw, ro mounts > in sequence and they stick fine. In fact they stick with the same > subvolume. >=20 > [root@f23m ]# mount /dev/sda7 /mnt/1 -o subvol=3Dhome > [root@f23m ]# mount /dev/sda7 /mnt/2 -o subvol=3Dhome,ro > [root@f23m ]# mount /dev/sda7 /mnt/3 -o subvol=3Dhome > [root@f23m ]# mount > [...snip...] > /dev/sda7 on /mnt/1 type btrfs > (rw,relatime,seclabel,ssd,space_cache,subvolid=3D258,subvol=3D/home) > /dev/sda7 on /mnt/2 type btrfs > (ro,relatime,seclabel,ssd,space_cache,subvolid=3D258,subvol=3D/home) > /dev/sda7 on /mnt/3 type btrfs > (rw,relatime,seclabel,ssd,space_cache,subvolid=3D258,subvol=3D/home) Not sure what you mean with "stick" here... I'd say the above has simply the following semantics: - the default for mounts is rw - thus /mnt/1 and /mnt/3 are rw, and 3 isn't rw, because 1 was In other words, if you change that to the following: # mount /dev/sda7 /mnt/1 -o subvol=3Dhome,ro # mount /dev/sda7 /mnt/2 -o subvol=3Dhome,ro # mount /dev/sda7 /mnt/3 -o subvol=3Dhome I'd expect that you get ro ro rw At least based on how I understood the whole system now. That was actually my question here: Q: In other words does mounting the same subvol *again* behave like -- bind mounts, i.e. the further mounts would get the options from the first mount? And I guess the A:(nswer) is: no, mount options affect the respective mountpoint (including any nested subvols below that) only (except of course it's a --bind mount. If one of the devs could confirm that semantics, I may find some time to update the wiki accordingly. 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