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authorPhillip Lougher <phillip@lougher.demon.co.uk>2011-02-28 16:32:39 +0000
committerPhillip Lougher <phillip@lougher.demon.co.uk>2011-02-28 18:35:36 +0000
commit4c1d204cde1470863e78aa0e6f55246c57f15038 (patch)
tree0e7ba1366188e7c34a35c00b3bc18bd57785cf07 /Documentation/filesystems
parent681ffe2e4316801529fdafe379743d1d41fe2086 (diff)
Squashfs: Update documentation to include compression options
Signed-off-by: Phillip Lougher <phillip@lougher.demon.co.uk>
Diffstat (limited to 'Documentation/filesystems')
-rw-r--r--Documentation/filesystems/squashfs.txt28
1 files changed, 19 insertions, 9 deletions
diff --git a/Documentation/filesystems/squashfs.txt b/Documentation/filesystems/squashfs.txt
index 66699afd66c..2d78f191184 100644
--- a/Documentation/filesystems/squashfs.txt
+++ b/Documentation/filesystems/squashfs.txt
@@ -59,12 +59,15 @@ obtained from this site also.
3. SQUASHFS FILESYSTEM DESIGN
-----------------------------
-A squashfs filesystem consists of a maximum of eight parts, packed together on a byte
-alignment:
+A squashfs filesystem consists of a maximum of nine parts, packed together on a
+byte alignment:
---------------
| superblock |
|---------------|
+ | compression |
+ | options |
+ |---------------|
| datablocks |
| & fragments |
|---------------|
@@ -91,7 +94,14 @@ the source directory, and checked for duplicates. Once all file data has been
written the completed inode, directory, fragment, export and uid/gid lookup
tables are written.
-3.1 Inodes
+3.1 Compression options
+-----------------------
+
+Compressors can optionally support compression specific options (e.g.
+dictionary size). If non-default compression options have been used, then
+these are stored here.
+
+3.2 Inodes
----------
Metadata (inodes and directories) are compressed in 8Kbyte blocks. Each
@@ -114,7 +124,7 @@ directory inode are defined: inodes optimised for frequently occurring
regular files and directories, and extended types where extra
information has to be stored.
-3.2 Directories
+3.3 Directories
---------------
Like inodes, directories are packed into compressed metadata blocks, stored
@@ -144,7 +154,7 @@ decompressed to do a lookup irrespective of the length of the directory.
This scheme has the advantage that it doesn't require extra memory overhead
and doesn't require much extra storage on disk.
-3.3 File data
+3.4 File data
-------------
Regular files consist of a sequence of contiguous compressed blocks, and/or a
@@ -163,7 +173,7 @@ Larger files use multiple slots, with 1.75 TiB files using all 8 slots.
The index cache is designed to be memory efficient, and by default uses
16 KiB.
-3.4 Fragment lookup table
+3.5 Fragment lookup table
-------------------------
Regular files can contain a fragment index which is mapped to a fragment
@@ -173,7 +183,7 @@ A second index table is used to locate these. This second index table for
speed of access (and because it is small) is read at mount time and cached
in memory.
-3.5 Uid/gid lookup table
+3.6 Uid/gid lookup table
------------------------
For space efficiency regular files store uid and gid indexes, which are
@@ -182,7 +192,7 @@ stored compressed into metadata blocks. A second index table is used to
locate these. This second index table for speed of access (and because it
is small) is read at mount time and cached in memory.
-3.6 Export table
+3.7 Export table
----------------
To enable Squashfs filesystems to be exportable (via NFS etc.) filesystems
@@ -196,7 +206,7 @@ This table is stored compressed into metadata blocks. A second index table is
used to locate these. This second index table for speed of access (and because
it is small) is read at mount time and cached in memory.
-3.7 Xattr table
+3.8 Xattr table
---------------
The xattr table contains extended attributes for each inode. The xattrs