From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from userp2120.oracle.com ([156.151.31.85]:47046 "EHLO userp2120.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751219AbeENCav (ORCPT ); Sun, 13 May 2018 22:30:51 -0400 Subject: Re: [PATCH 4/4] design: merge both metadata integrity chapters References: <152623082465.10242.9458731018482450171.stgit@magnolia> <152623084927.10242.11550787265390407416.stgit@magnolia> From: Allison Henderson Message-ID: <49f79922-c59f-ebe0-24fc-f9902156ddff@oracle.com> Date: Sun, 13 May 2018 19:30:45 -0700 MIME-Version: 1.0 In-Reply-To: <152623084927.10242.11550787265390407416.stgit@magnolia> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Sender: linux-xfs-owner@vger.kernel.org List-ID: List-Id: xfs To: "Darrick J. Wong" Cc: linux-xfs@vger.kernel.org, azarus@posteo.net Reviewed by: Allison Henderson On 05/13/2018 10:00 AM, Darrick J. Wong wrote: > From: Darrick J. Wong > > We don't need to have two chapters on metadata integrity, so merge them. > > Signed-off-by: Darrick J. Wong > --- > .../metadata_integrity.asciidoc | 36 -------------------- > .../self_describing_metadata.asciidoc | 27 ++++++++++++++- > .../xfs_filesystem_structure.asciidoc | 2 - > 3 files changed, 26 insertions(+), 39 deletions(-) > delete mode 100644 design/XFS_Filesystem_Structure/metadata_integrity.asciidoc > > > diff --git a/design/XFS_Filesystem_Structure/metadata_integrity.asciidoc b/design/XFS_Filesystem_Structure/metadata_integrity.asciidoc > deleted file mode 100644 > index f948d5e..0000000 > --- a/design/XFS_Filesystem_Structure/metadata_integrity.asciidoc > +++ /dev/null > @@ -1,36 +0,0 @@ > -= Metadata Integrity > - > -Prior to version 5, most XFS metadata blocks contained a magic number that > -could provide a minimal sanity check that a block read off the disk contained > -the same type of data that the code thought it was reading off the disk. > -However, this was insufficient -- given a correct type code, it was still > -impossible to tell if the block was from a previous filesystem, or happened to > -be owned by something else, or had been written to the wrong location on disk. > -Furthermore, not all metadata blocks had magic numbers -- remote extended > -attributes and extent symbolic links had no protection at all. > - > -Therefore, the version 5 disk format introduced larger headers for all metadata > -types, which enable the filesystem to check information being read from the > -disk more rigorously. Metadata integrity fields now include: > - > -* *Magic* numbers, to classify all types of metadata. This is unchanged from v4. > -* A copy of the filesystem *UUID*, to confirm that a given disk block is connected to the superblock. > -* The *owner*, to avoid accessing a piece of metadata which belongs to some other part of the filesystem. > -* The filesystem *block number*, to detect misplaced writes. > -* The *log serial number* of the last write to this block, to avoid replaying obsolete log entries. > -* A CRC32c *checksum* of the entire block, to detect minor corruption. > - > -Metadata integrity coverage has been extended to all metadata blocks in the > -filesystem, with the following notes: > - > -* Inodes can have multiple ``owners'' in the directory tree; therefore the record contains the inode number instead of an owner or a block number. > -* Superblocks have no owners. > -* The disk quota file has no owner or block numbers. > -* Metadata owned by files list the inode number as the owner. > -* Per-AG data and B+tree blocks list the AG number as the owner. > -* Per-AG header sectors don't list owners or block numbers, since they have fixed locations. > -* Remote attribute blocks are not logged and therefore the LSN must be -1. > - > -This functionality enables XFS to decide that a block contents are so > -unexpected that it should stop immediately. Unfortunately checksums do not > -allow for automatic correction. Please keep regular backups, as always. > diff --git a/design/XFS_Filesystem_Structure/self_describing_metadata.asciidoc b/design/XFS_Filesystem_Structure/self_describing_metadata.asciidoc > index c3038b9..c79e865 100644 > --- a/design/XFS_Filesystem_Structure/self_describing_metadata.asciidoc > +++ b/design/XFS_Filesystem_Structure/self_describing_metadata.asciidoc > @@ -1,4 +1,4 @@ > -= XFS Self Describing Metadata > += Metadata Integrity > > == Introduction > > @@ -30,6 +30,31 @@ up, the more likely that the cause will be lost in the noise. Hence the primary > concern for supporting PB scale filesystems is minimising the time and effort > required for basic forensic analysis of the filesystem structure. > > +Therefore, the version 5 disk format introduced larger headers for all metadata > +types, which enable the filesystem to check information being read from the > +disk more rigorously. Metadata integrity fields now include: > + > +* *Magic* numbers, to classify all types of metadata. This is unchanged from v4. > +* A copy of the filesystem *UUID*, to confirm that a given disk block is connected to the superblock. > +* The *owner*, to avoid accessing a piece of metadata which belongs to some other part of the filesystem. > +* The filesystem *block number*, to detect misplaced writes. > +* The *log serial number* of the last write to this block, to avoid replaying obsolete log entries. > +* A CRC32c *checksum* of the entire block, to detect minor corruption. > + > +Metadata integrity coverage has been extended to all metadata blocks in the > +filesystem, with the following notes: > + > +* Inodes can have multiple ``owners'' in the directory tree; therefore the record contains the inode number instead of an owner or a block number. > +* Superblocks have no owners. > +* The disk quota file has no owner or block numbers. > +* Metadata owned by files list the inode number as the owner. > +* Per-AG data and B+tree blocks list the AG number as the owner. > +* Per-AG header sectors don't list owners or block numbers, since they have fixed locations. > +* Remote attribute blocks are not logged and therefore the LSN must be -1. > + > +This functionality enables XFS to decide that a block contents are so > +unexpected that it should stop immediately. Unfortunately checksums do not > +allow for automatic correction. Please keep regular backups, as always. > > == Self Describing Metadata > > diff --git a/design/XFS_Filesystem_Structure/xfs_filesystem_structure.asciidoc b/design/XFS_Filesystem_Structure/xfs_filesystem_structure.asciidoc > index 15ab185..5c1642c 100644 > --- a/design/XFS_Filesystem_Structure/xfs_filesystem_structure.asciidoc > +++ b/design/XFS_Filesystem_Structure/xfs_filesystem_structure.asciidoc > @@ -46,8 +46,6 @@ log items which are formatted in host order. > > include::overview.asciidoc[] > > -include::metadata_integrity.asciidoc[] > - > include::self_describing_metadata.asciidoc[] > > include::delayed_logging.asciidoc[] > > -- > To unsubscribe from this list: send the line "unsubscribe linux-xfs" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at https://urldefense.proofpoint.com/v2/url?u=http-3A__vger.kernel.org_majordomo-2Dinfo.html&d=DwICaQ&c=RoP1YumCXCgaWHvlZYR8PZh8Bv7qIrMUB65eapI_JnE&r=LHZQ8fHvy6wDKXGTWcm97burZH5sQKHRDMaY1UthQxc&m=iLHKZWAtYwIbFJOpHF3Mqhp6qAE9a2KWfS-dS7EIHAA&s=FTVB8zpRJT8n6OJKTtOSb_PHsCs5AEcZZLnJ5LyhKc4&e=