From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-io0-f175.google.com ([209.85.223.175]:35382 "EHLO mail-io0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752599AbbLHU3e (ORCPT ); Tue, 8 Dec 2015 15:29:34 -0500 Received: by ioc74 with SMTP id 74so36665798ioc.2 for ; Tue, 08 Dec 2015 12:29:33 -0800 (PST) Subject: Re: [PATCH] btrfs: Introduce new mount option to disable tree log replay To: Christoph Anton Mitterer , Eric Sandeen , Chandan Rajendra References: <1449468402-27914-1-git-send-email-quwenruo@cn.fujitsu.com> <5665B359.2050906@redhat.com> <2856934.1tulUexfpA@localhost.localdomain> <5665C1F2.8020407@redhat.com> <1449521684.6881.13.camel@scientia.net> <566610FA.1080408@redhat.com> <5666C9F7.2030509@gmail.com> <1449602402.6649.6.camel@scientia.net> Cc: Qu Wenruo , linux-btrfs@vger.kernel.org From: Austin S Hemmelgarn Message-ID: <56673DA5.9030607@gmail.com> Date: Tue, 8 Dec 2015 15:29:25 -0500 MIME-Version: 1.0 In-Reply-To: <1449602402.6649.6.camel@scientia.net> Content-Type: multipart/signed; protocol="application/pkcs7-signature"; micalg=sha-512; boundary="------------ms060508040003060304020307" Sender: linux-btrfs-owner@vger.kernel.org List-ID: This is a cryptographically signed message in MIME format. --------------ms060508040003060304020307 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable On 2015-12-08 14:20, Christoph Anton Mitterer wrote: > On Tue, 2015-12-08 at 07:15 -0500, Austin S Hemmelgarn wrote: >> Despite this, it really isn't a widely known or well documented >> behavior >> outside of developers, forensic specialists, and people who have had >> to >> deal with the implications it has on data recovery. There really >> isn't >> any way that the user would know about it without being explicitly >> told, >> and it's something that can have a serious impact on being able to >> recover a broken filesystem. TBH, I really feel that _every_ >> filesystem's documentation should have something about how to make it >> mount truly read-only, even if it's just a reference to how to mark >> the >> block device read-only. > Exactly what I've meant. > > And the developers here, should definitely consider that every normal > end-user, may easily assume the role of e.g. a forensics specialist > (especially with btrfs ;-) ), when recovery in case of corruptions is > tried. > > > I don't think that "it has always been improperly documented" (i.e. the= > "ro" option) is a good excuse to continue doing it that way =3D) Agreed, 'but it's always been that way' is never a valid argument, and=20 the fact that people who have been working on UNIX for decades know it=20 doesn't mean that it's something that people will just inherently know.=20 The only reason it was that way to begin with is because it was=20 assumed that everyone dealing with computers had a huge amount of domain = specific knowledge of them (this was a valid assumption back in 1970, it = hasn't been a valid assumption since at least 1990). Stuff that seems obvious to people who have been working on it for years = isn't necessarily obvious to people who have limited experience with it=20 (I recently had to explain to a friend who had almost no networking=20 background how IP addresses are just an abstraction for MAC addresses,=20 and how it's not possible to block WiFi access based on an IP address;=20 it took me three tries and eventually making the analogy of street=20 addresses being an abstraction for geographical coordinates before he=20 finally got it). TBH, the only reason I knew about this rather annoying detail of=20 filesystem implementation before using BTRFS is because of dealing with=20 shared storage on VM's (that was an interesting week of debugging and=20 restoring backups before I finally figured out what was going on). --------------ms060508040003060304020307 Content-Type: application/pkcs7-signature; name="smime.p7s" Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename="smime.p7s" Content-Description: S/MIME Cryptographic Signature MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgMFADCABgkqhkiG9w0BBwEAAKCC Brgwgga0MIIEnKADAgECAgMRLfgwDQYJKoZIhvcNAQENBQAweTEQMA4GA1UEChMHUm9vdCBD QTEeMBwGA1UECxMVaHR0cDovL3d3dy5jYWNlcnQub3JnMSIwIAYDVQQDExlDQSBDZXJ0IFNp Z25pbmcgQXV0aG9yaXR5MSEwHwYJKoZIhvcNAQkBFhJzdXBwb3J0QGNhY2VydC5vcmcwHhcN MTUwOTIxMTEzNTEzWhcNMTYwMzE5MTEzNTEzWjBjMRgwFgYDVQQDEw9DQWNlcnQgV29UIFVz ZXIxIzAhBgkqhkiG9w0BCQEWFGFoZmVycm9pbjdAZ21haWwuY29tMSIwIAYJKoZIhvcNAQkB FhNhaGVtbWVsZ0BvaGlvZ3QuY29tMIICIjANBgkqhkiG9w0BAQEFAAOCAg8AMIICCgKCAgEA nQ/81tq0QBQi5w316VsVNfjg6kVVIMx760TuwA1MUaNQgQ3NyUl+UyFtjhpkNwwChjgAqfGd LIMTHAdObcwGfzO5uI2o1a8MHVQna8FRsU3QGouysIOGQlX8jFYXMKPEdnlt0GoQcd+BtESr pivbGWUEkPs1CwM6WOrs+09bAJP3qzKIr0VxervFrzrC5Dg9Rf18r9WXHElBuWHg4GYHNJ2V Ab8iKc10h44FnqxZK8RDN8ts/xX93i9bIBmHnFfyNRfiOUtNVeynJbf6kVtdHP+CRBkXCNRZ qyQT7gbTGD24P92PS2UTmDfplSBcWcTn65o3xWfesbf02jF6PL3BCrVnDRI4RgYxG3zFBJuG qvMoEODLhHKSXPAyQhwZINigZNdw5G1NqjXqUw+lIqdQvoPijK9J3eijiakh9u2bjWOMaleI SMRR6XsdM2O5qun1dqOrCgRkM0XSNtBQ2JjY7CycIx+qifJWsRaYWZz0aQU4ZrtAI7gVhO9h pyNaAGjvm7PdjEBiXq57e4QcgpwzvNlv8pG1c/hnt0msfDWNJtl3b6elhQ2Pz4w/QnWifZ8E BrFEmjeeJa2dqjE3giPVWrsH+lOvQQONsYJOuVb8b0zao4vrWeGmW2q2e3pdv0Axzm/60cJQ haZUv8+JdX9ZzqxOm5w5eUQSclt84u+D+hsCAwEAAaOCAVkwggFVMAwGA1UdEwEB/wQCMAAw VgYJYIZIAYb4QgENBEkWR1RvIGdldCB5b3VyIG93biBjZXJ0aWZpY2F0ZSBmb3IgRlJFRSBo ZWFkIG92ZXIgdG8gaHR0cDovL3d3dy5DQWNlcnQub3JnMA4GA1UdDwEB/wQEAwIDqDBABgNV HSUEOTA3BggrBgEFBQcDBAYIKwYBBQUHAwIGCisGAQQBgjcKAwQGCisGAQQBgjcKAwMGCWCG SAGG+EIEATAyBggrBgEFBQcBAQQmMCQwIgYIKwYBBQUHMAGGFmh0dHA6Ly9vY3NwLmNhY2Vy dC5vcmcwMQYDVR0fBCowKDAmoCSgIoYgaHR0cDovL2NybC5jYWNlcnQub3JnL3Jldm9rZS5j cmwwNAYDVR0RBC0wK4EUYWhmZXJyb2luN0BnbWFpbC5jb22BE2FoZW1tZWxnQG9oaW9ndC5j b20wDQYJKoZIhvcNAQENBQADggIBADMnxtSLiIunh/TQcjnRdf63yf2D8jMtYUm4yDoCF++J jCXbPQBGrpCEHztlNSGIkF3PH7ohKZvlqF4XePWxpY9dkr/pNyCF1PRkwxUURqvuHXbu8Lwn 8D3U2HeOEU3KmrfEo65DcbanJCMTTW7+mU9lZICPP7ZA9/zB+L0Gm1UNFZ6AU50N/86vjQfY WgkCd6dZD4rQ5y8L+d/lRbJW7ZGEQw1bSFVTRpkxxDTOwXH4/GpQfnfqTAtQuJ1CsKT12e+H NSD/RUWGTr289dA3P4nunBlz7qfvKamxPymHeBEUcuICKkL9/OZrnuYnGROFwcdvfjGE5iLB kjp/ttrY4aaVW5EsLASNgiRmA6mbgEAMlw3RwVx0sVelbiIAJg9Twzk4Ct6U9uBKiJ8S0sS2 8RCSyTmCRhJs0vvva5W9QUFGmp5kyFQEoSfBRJlbZfGX2ehI2Hi3U2/PMUm2ONuQG1E+a0AP u7I0NJc/Xil7rqR0gdbfkbWp0a+8dAvaM6J00aIcNo+HkcQkUgtfrw+C2Oyl3q8IjivGXZqT 5UdGUb2KujLjqjG91Dun3/RJ/qgQlotH7WkVBs7YJVTCxfkdN36rToPcnMYOI30FWa0Q06gn F6gUv9/mo6riv3A5bem/BdbgaJoPnWQD9D8wSyci9G4LKC+HQAMdLmGoeZfpJzKHMYIE0TCC BM0CAQEwgYAweTEQMA4GA1UEChMHUm9vdCBDQTEeMBwGA1UECxMVaHR0cDovL3d3dy5jYWNl cnQub3JnMSIwIAYDVQQDExlDQSBDZXJ0IFNpZ25pbmcgQXV0aG9yaXR5MSEwHwYJKoZIhvcN AQkBFhJzdXBwb3J0QGNhY2VydC5vcmcCAxEt+DANBglghkgBZQMEAgMFAKCCAiEwGAYJKoZI hvcNAQkDMQsGCSqGSIb3DQEHATAcBgkqhkiG9w0BCQUxDxcNMTUxMjA4MjAyOTI1WjBPBgkq hkiG9w0BCQQxQgRAP2JTsj+MGSt14hhc6R78pyNPwSoadW3TvOOjc7BYV8Ztq1s1Pb/SACWV cO7CHqWZz6j/KymJlhFFGft1jo6fiTBsBgkqhkiG9w0BCQ8xXzBdMAsGCWCGSAFlAwQBKjAL BglghkgBZQMEAQIwCgYIKoZIhvcNAwcwDgYIKoZIhvcNAwICAgCAMA0GCCqGSIb3DQMCAgFA MAcGBSsOAwIHMA0GCCqGSIb3DQMCAgEoMIGRBgkrBgEEAYI3EAQxgYMwgYAweTEQMA4GA1UE ChMHUm9vdCBDQTEeMBwGA1UECxMVaHR0cDovL3d3dy5jYWNlcnQub3JnMSIwIAYDVQQDExlD QSBDZXJ0IFNpZ25pbmcgQXV0aG9yaXR5MSEwHwYJKoZIhvcNAQkBFhJzdXBwb3J0QGNhY2Vy dC5vcmcCAxEt+DCBkwYLKoZIhvcNAQkQAgsxgYOggYAweTEQMA4GA1UEChMHUm9vdCBDQTEe MBwGA1UECxMVaHR0cDovL3d3dy5jYWNlcnQub3JnMSIwIAYDVQQDExlDQSBDZXJ0IFNpZ25p bmcgQXV0aG9yaXR5MSEwHwYJKoZIhvcNAQkBFhJzdXBwb3J0QGNhY2VydC5vcmcCAxEt+DAN BgkqhkiG9w0BAQEFAASCAgBTynTmQsHA0WVv04LMzztdxyhEAWdE3RIdhlc6A7d/LYUct48x P5wj0Yym5iLLpWeTlpPu5fHDL9zyqBZ9/HzmHurFvfoVMMxm2GYEIeSTN8DXba/PHEzDmEe2 fOHhaoOSQCJXjSPyXzBvlqQxqk9EzvTViRaJKln7fjb/i2yRMP0APqv/KfZr6jtdX83qWvPw +EyzKQGRgLzWNFYCGWE0jzX8TSbYKakirsM3ZuQQEn/AYmnFeXQOtABYOEhAmNL/EftyfNh1 A5o8kmQpk4ofYDME/ZI8Wa2E9Vwezzpwq6DpocBBUBvsLvpdPprwGJ+nDMWXLmNDF6qOrYtd f4sUlkPpVPl30qM8leV8pt79bkH1qoEwXscpwfjA00SY1G6ax7GzwL+5HJ7gmf56jNQ9FR6c QvbkhlkuVMmj9TDVSKle/I35EzjyKhsUnpH/FJOW1lqA/27BGG/G4m++zW2oceuxCQ0tcCBu n/AFlE3REG9G5iYvVWKzGMtM+mo26omN2PZXWQHYGFrADkpeXEELDKbEIjdzdKgQTUn5/oKP ct455SJ27aSEojRpWvXw8xiPYGBGIb5mV2xMyL86wZQJ7xEJQ0fGa9h+9JDf6RcM7//AMVLN L80MbWh33ZrqrVHOkZUMAHBigUVTr8BI9Y8Rf/V9/AhmfbwFrYuUB0mfTgAAAAAAAA== --------------ms060508040003060304020307--