From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mailgw-02.dd24.net ([193.46.215.43]:41217 "EHLO mailgw-02.dd24.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751658AbbLJVN3 (ORCPT ); Thu, 10 Dec 2015 16:13:29 -0500 Received: from mailpolicy-01.live.igb.homer.key-systems.net (mailpolicy-02.live.igb.homer.key-systems.net [192.168.1.27]) by mailgw-02.dd24.net (Postfix) with ESMTP id 083E45FBEB for ; Thu, 10 Dec 2015 21:13:27 +0000 (UTC) Received: from mailgw-02.dd24.net ([192.168.1.36]) by mailpolicy-01.live.igb.homer.key-systems.net (mailpolicy-02.live.igb.homer.key-systems.net [192.168.1.25]) (amavisd-new, port 10236) with ESMTP id w7fLj2mb1Rn8 for ; Thu, 10 Dec 2015 21:13:24 +0000 (UTC) Received: from heisenberg.fritz.box (ppp-93-104-122-99.dynamic.mnet-online.de [93.104.122.99]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mailgw-02.dd24.net (Postfix) with ESMTPSA for ; Thu, 10 Dec 2015 21:13:24 +0000 (UTC) Message-ID: <1449782004.7032.19.camel@scientia.net> Subject: Re: subvols, ro- and bind mounts - how? From: Christoph Anton Mitterer To: linux-btrfs@vger.kernel.org Date: Thu, 10 Dec 2015 22:13:24 +0100 In-Reply-To: References: <1448340960.14125.51.camel@scientia.net> <1448400350.21291.88.camel@scientia.net> <1449635882.20578.2.camel@scientia.net> Content-Type: multipart/signed; micalg="sha-512"; protocol="application/x-pkcs7-signature"; boundary="=-7ltuvltyo4YKojjU6KvJ" Mime-Version: 1.0 Sender: linux-btrfs-owner@vger.kernel.org List-ID: --=-7ltuvltyo4YKojjU6KvJ Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Hey. I'd have an additional question about subvols O:-) Given the following setup: 5 | +--root (subvol, /) =C2=A0 =C2=A0+-- mnt (dir) with the following done: - init 1 - remount,ro / (i.e. the subvol root) - mount /dev/btrfs-device /mnt (i.e. mount the top subvol at /mnt) The following happened: - / was ro-mounted (obviously, at least one thing that I had expected =C2=A0 correctly) - /mnt was ro-mounted either (and the /mnt/root/ nested subvol then as =C2=A0 well). =C2=A0 =3D> why is /mnt (i.e. the top level subvol) mounted ro?? =C2=A0 =3D> I would have expected that, since / (i.e. the subvol "root" is = ro =C2=A0 =C2=A0 =C2=A0mounted), it's also ro mounted as the nested subvol bel= ow 5, i.e. =C2=A0 =C2=A0 =C2=A0my naive thinking was in terms of logic: =C2=A0 =C2=A0 =C2=A0"/ mounted ro" =3D> "subvol root is mounted ro (everywh= ere)" =C2=A0 =C2=A0 =C2=A0 =C2=A0=3D> "thus /mnt/root/ is mounted ro as well" However, the later doesn't seem to be true, cause then I did: - remount,rw /mnt =3D> now /mnt/*, including /mnt/root/* was rw moutned So I guess my assumption of subvols behaving more or less as if they'd be a fs (and thus mounted at one place ro =3D> everywhere ro) is not true, is it? Do, ro,rw (and possibly others) instead only affect the respective mountpoint? And automatically any nested subvols of that mountpoint? So I could have basically: /mount-point1/subvol-a ; ro, noexec /mount-point2/subvol-a ; rw, compress=3Dyes /root ; rw, compress=3Dno /root/here/it/is/nested/subvol-a ; (no mountpoint) (with subvol-a being the same subvol) And when I write via mount-point1 I'd get an error, but via mount- point2 it works and in addition I get compression, while when writing via the /root mountpoint, where it is nested, I'd get the rw and compress=3Dno from the "parent" mountpoint /root Does that sounds correct? It seems to make sense actually, though it's a bit unfamiliar... if I'm not correctly wrong, than e.g. in terms of ext* I cannot have the same fs mounted with different settings,... of course I cannot have it mounted twice at all, but speaking of bind mounts. So I guess, that when I'd do --bind mounts instead, I actually do get the "old" behaviour, i.e. when the source is ro, then the --bind mount's target is also forcibly ro. Still, one unclear thing, why got /mnt mounted ro very above? Thanks, Chris. btw: Not sure if I just missed it, but I guess the above should be more or less documented, showing people that mounting subvols (especially when mounting the same several times, either directly or as nested subvol) has these implications. --=-7ltuvltyo4YKojjU6KvJ Content-Type: application/x-pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgMFADCABgkqhkiG9w0BBwEAAKCCEZIw ggW/MIIDp6ADAgECAgMCOakwDQYJKoZIhvcNAQENBQAwVDEUMBIGA1UEChMLQ0FjZXJ0IEluYy4x HjAcBgNVBAsTFWh0dHA6Ly93d3cuQ0FjZXJ0Lm9yZzEcMBoGA1UEAxMTQ0FjZXJ0IENsYXNzIDMg Um9vdDAeFw0xNDA2MTIxNjM2MThaFw0xNjA2MTExNjM2MThaMHwxITAfBgNVBAMTGENocmlzdG9w aCBBbnRvbiBNaXR0ZXJlcjEkMCIGCSqGSIb3DQEJARYVY2FsZXN0eW9Ac2NpZW50aWEubmV0MTEw LwYJKoZIhvcNAQkBFiJtYWlsQGNocmlzdG9waC5hbnRvbi5taXR0ZXJlci5uYW1lMIIBIjANBgkq hkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA4phP/j9vT9dZT+k3ffHxvRWMOuzBnu5O3Fl4y2+WL7pL 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