forked from Minki/linux
Squashfs: Update documentation to include compression options
Signed-off-by: Phillip Lougher <phillip@lougher.demon.co.uk>
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@ -59,12 +59,15 @@ obtained from this site also.
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3. SQUASHFS FILESYSTEM DESIGN
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-----------------------------
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A squashfs filesystem consists of a maximum of eight parts, packed together on a byte
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alignment:
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A squashfs filesystem consists of a maximum of nine parts, packed together on a
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byte alignment:
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---------------
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| superblock |
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|---------------|
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| compression |
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| options |
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|---------------|
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| datablocks |
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| & fragments |
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|---------------|
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@ -91,7 +94,14 @@ the source directory, and checked for duplicates. Once all file data has been
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written the completed inode, directory, fragment, export and uid/gid lookup
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tables are written.
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3.1 Inodes
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3.1 Compression options
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-----------------------
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Compressors can optionally support compression specific options (e.g.
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dictionary size). If non-default compression options have been used, then
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these are stored here.
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3.2 Inodes
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----------
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Metadata (inodes and directories) are compressed in 8Kbyte blocks. Each
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@ -114,7 +124,7 @@ directory inode are defined: inodes optimised for frequently occurring
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regular files and directories, and extended types where extra
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information has to be stored.
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3.2 Directories
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3.3 Directories
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---------------
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Like inodes, directories are packed into compressed metadata blocks, stored
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@ -144,7 +154,7 @@ decompressed to do a lookup irrespective of the length of the directory.
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This scheme has the advantage that it doesn't require extra memory overhead
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and doesn't require much extra storage on disk.
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3.3 File data
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3.4 File data
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-------------
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Regular files consist of a sequence of contiguous compressed blocks, and/or a
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@ -163,7 +173,7 @@ Larger files use multiple slots, with 1.75 TiB files using all 8 slots.
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The index cache is designed to be memory efficient, and by default uses
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16 KiB.
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3.4 Fragment lookup table
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3.5 Fragment lookup table
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-------------------------
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Regular files can contain a fragment index which is mapped to a fragment
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@ -173,7 +183,7 @@ A second index table is used to locate these. This second index table for
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speed of access (and because it is small) is read at mount time and cached
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in memory.
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3.5 Uid/gid lookup table
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3.6 Uid/gid lookup table
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------------------------
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For space efficiency regular files store uid and gid indexes, which are
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@ -182,7 +192,7 @@ stored compressed into metadata blocks. A second index table is used to
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locate these. This second index table for speed of access (and because it
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is small) is read at mount time and cached in memory.
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3.6 Export table
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3.7 Export table
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----------------
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To enable Squashfs filesystems to be exportable (via NFS etc.) filesystems
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@ -196,7 +206,7 @@ This table is stored compressed into metadata blocks. A second index table is
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used to locate these. This second index table for speed of access (and because
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it is small) is read at mount time and cached in memory.
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3.7 Xattr table
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3.8 Xattr table
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---------------
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The xattr table contains extended attributes for each inode. The xattrs
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