Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
---
design/XFS_Filesystem_Structure/docinfo.xml | 1
design/XFS_Filesystem_Structure/magic.asciidoc | 86 ++++++++++++++++++++
.../xfs_filesystem_structure.asciidoc | 2
3 files changed, 89 insertions(+)
create mode 100644 design/XFS_Filesystem_Structure/magic.asciidoc
diff --git a/design/XFS_Filesystem_Structure/docinfo.xml
b/design/XFS_Filesystem_Structure/docinfo.xml
index 8ed38d9..6189fd6 100644
--- a/design/XFS_Filesystem_Structure/docinfo.xml
+++ b/design/XFS_Filesystem_Structure/docinfo.xml
@@ -103,6 +103,7 @@
<member>Add v5 fields.</member>
<member>Discuss metadata integrity.</member>
<member>Document the free inode B+tree.</member>
+ <member>Create an index of magic
numbers.</member>
</simplelist>
</revdescription>
</revision>
diff --git a/design/XFS_Filesystem_Structure/magic.asciidoc
b/design/XFS_Filesystem_Structure/magic.asciidoc
new file mode 100644
index 0000000..301cfa0
--- /dev/null
+++ b/design/XFS_Filesystem_Structure/magic.asciidoc
@@ -0,0 +1,86 @@
+= Magic Numbers
+
+These are the magic numbers that are known to XFS, along with links to the
+relevant chapters. Magic numbers tend to have consistent locations:
+
+* 32-bit magic numbers are always at offset zero in the block.
+* 16-bit magic numbers for the directory and attribute B+tree are at offset
eight.
+* The quota magic number is at offset zero.
+* The inode magic is at the beginning of each inode.
+
+[options="header"]
+|=====
+| Flag | Hexadecimal | ASCII | Data structure
+| +XFS_SB_MAGIC+ | 0x58465342 | XFSB |
xref:Superblocks[Superblock]
+| +XFS_AGF_MAGIC+ | 0x58414746 | XAGF |
xref:AG_Free_Space_Block[Free Space]
+| +XFS_AGI_MAGIC+ | 0x58414749 | XAGI |
xref:Inode_Information[Inode Information]
+| +XFS_AGFL_MAGIC+ | 0x5841464c | XAFL |
xref:AG_Free_List[Free Space List], v5 only
+| +XFS_DINODE_MAGIC+ | 0x494e | IN |
xref:Inode_Core[Inodes]
+| +XFS_DQUOT_MAGIC+ | 0x4451 | DQ |
xref:Quota_Inodes[Quota Inodes]
+| +XFS_SYMLINK_MAGIC+ | 0x58534c4d | XSLM |
xref:Extent_Symbolic_Links[Symbolic Links]
+| +XFS_ABTB_MAGIC+ | 0x41425442 | ABTB |
xref:AG_Free_Space_Btrees[Free Space by Block B+tree]
+| +XFS_ABTB_CRC_MAGIC+ | 0x41423342 | AB3B |
xref:AG_Free_Space_Btrees[Free Space by Block B+tree], v5 only
+| +XFS_ABTC_MAGIC+ | 0x41425443 | ABTC |
xref:AG_Free_Space_Btrees[Free Space by Size B+tree]
+| +XFS_ABTC_CRC_MAGIC+ | 0x41423343 | AB3C |
xref:AG_Free_Space_Btrees[Free Space by Size B+tree], v5 only
+| +XFS_IBT_MAGIC+ | 0x49414254 | IABT |
xref:Inode_Btrees[Inode B+tree]
+| +XFS_IBT_CRC_MAGIC+ | 0x49414233 | IAB3 |
xref:Inode_Btrees[Inode B+tree], v5 only
+| +XFS_FIBT_MAGIC+ | 0x46494254 | FIBT |
xref:Inode_Btrees[Free Inode B+tree]
+| +XFS_FIBT_CRC_MAGIC+ | 0x46494233 | FIB3 |
xref:Inode_Btrees[Free Inode B+tree], v5 only
+| +XFS_BMAP_MAGIC+ | 0x424d4150 | BMAP |
xref:Btree_Extent_List[B+Tree Extent List]
+| +XFS_BMAP_CRC_MAGIC+ | 0x424d4133 | BMA3 |
xref:Btree_Extent_List[B+Tree Extent List], v5 only
+| +XLOG_HEADER_MAGIC_NUM+ | 0xfeedbabe | | xref:Log_Records[Log
Records]
+| +XFS_DA_NODE_MAGIC+ | 0xfebe | |
xref:Directory_Attribute_Internal_Node[Directory/Attribute Node]
+| +XFS_DA3_NODE_MAGIC+ | 0x3ebe | |
xref:Directory_Attribute_Internal_Node[Directory/Attribute Node], v5 only
+| +XFS_DIR2_BLOCK_MAGIC+ | 0x58443242 | XD2B |
xref:Block_Directories[Block Directory Data]
+| +XFS_DIR3_BLOCK_MAGIC+ | 0x58444233 | XDB3 |
xref:Block_Directories[Block Directory Data], v5 only
+| +XFS_DIR2_DATA_MAGIC+ | 0x58443244 | XD2D |
xref:Leaf_Directories[Leaf Directory Data]
+| +XFS_DIR3_DATA_MAGIC+ | 0x58444433 | XDD3 |
xref:Leaf_Directories[Leaf Directory Data], v5 only
+| +XFS_DIR2_LEAF1_MAGIC+ | 0xd2f1 | |
xref:Leaf_Directories[Leaf Directory]
+| +XFS_DIR3_LEAF1_MAGIC+ | 0x3df1 | |
xref:Leaf_Directories[Leaf Directory], v5 only
+| +XFS_DIR2_LEAFN_MAGIC+ | 0xd2ff | |
xref:Node_Directories[Node Directory]
+| +XFS_DIR3_LEAFN_MAGIC+ | 0x3dff | |
xref:Node_Directories[Node Directory], v5 only
+| +XFS_DIR2_FREE_MAGIC+ | 0x58443246 | XD2F |
xref:Node_Directories[Node Directory Free Space]
+| +XFS_DIR3_FREE_MAGIC+ | 0x58444633 | XDF3 |
xref:Node_Directories[Node Directory Free Space], v5 only
+| +XFS_ATTR_LEAF_MAGIC+ | 0xfbee | |
xref:Leaf_Attributes[Leaf Attribute]
+| +XFS_ATTR3_LEAF_MAGIC+ | 0x3bee | |
xref:Leaf_Attributes[Leaf Attribute], v5 only
+| +XFS_ATTR3_RMT_MAGIC+ | 0x5841524d | XARM |
xref:Remote_Values[Remote Attribute Value], v5 only
+|=====
+
+The magic numbers for log items are at offset zero in each log item, but items
+are not aligned to blocks.
+
+[options="header"]
+|=====
+| Flag | Hexadecimal | ASCII | Data structure
+| +XFS_TRANS_HEADER_MAGIC+ | 0x5452414e | TRAN |
xref:Log_Transaction_Headers[Log Transactions]
+| +XFS_LI_EFI+ | 0x1236 | |
xref:EFI_Log_Item[Extent Freeing Intent Log Item]
+| +XFS_LI_EFD+ | 0x1237 | |
xref:EFD_Log_Item[Extent Freeing Done Log Item]
+| +XFS_LI_IUNLINK+ | 0x1238 | | Unknown?
+| +XFS_LI_INODE+ | 0x123b | |
xref:Inode_Log_Item[Inode Updates Log Item]
+| +XFS_LI_BUF+ | 0x123c | |
xref:Buffer_Log_Item[Buffer Writes Log Item]
+| +XFS_LI_DQUOT+ | 0x123d | |
xref:Quota_Update_Log_Item[Update Quota Log Item]
+| +XFS_LI_QUOTAOFF+ | 0x123e | |
xref:Quota_Off_Log_Item[Quota Off Log Item]
+| +XFS_LI_ICREATE+ | 0x123f | |
xref:Inode_Create_Log_Item[Inode Creation Log Item]
+|=====
+
+= Theoretical Limits
+
+XFS can create really big filesystems!
+
+[options="header"]
+|=====
+| Item | 1KiB blocks | 4KiB blocks | 64KiB blocks
+| Blocks | 2^52^ | 2^52^ | 2^52^
+| Inodes | 2^63^ | 2^63^ | 2^64^
+| Allocation Groups | 2^32^ | 2^32^ | 2^32^
+| File System Size | 8EiB | 8EiB | 8EiB
+| Blocks per AG | 2^31^ | 2^31^ | 2^31^
+| Inodes per AG | 2^32^ | 2^32^ | 2^32^
+| Max AG Size | 2TiB | 8TiB | 128TiB
+| Blocks Per File | 2^54^ | 2^54^ | 2^54^
+| File Size | 8EiB | 8EiB | 8EiB
+| Max Dir Size | 32GiB | 32GiB | 32GiB
+|=====
+
+Linux doesn't suppport files or devices larger than 8EiB, so the block
+limitations are largely ignorable.
diff --git a/design/XFS_Filesystem_Structure/xfs_filesystem_structure.asciidoc
b/design/XFS_Filesystem_Structure/xfs_filesystem_structure.asciidoc
index 8aacbb7..0ab4906 100644
--- a/design/XFS_Filesystem_Structure/xfs_filesystem_structure.asciidoc
+++ b/design/XFS_Filesystem_Structure/xfs_filesystem_structure.asciidoc
@@ -50,6 +50,8 @@ include::metadata_integrity.asciidoc[]
include::common_types.asciidoc[]
+include::magic.asciidoc[]
+
// return titles to normal
:leveloffset: 0
|