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Squashfs: Update documentation to include compression options

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Signed-off-by: Phillip Lougher <phillip@lougher.demon.co.uk>
This commit is contained in:
Phillip Lougher 2011-02-28 16:32:39 +00:00
parent 681ffe2e43
commit 4c1d204cde
1 changed files with 19 additions and 9 deletions
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28
Documentation/filesystems/squashfs.txt
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@ -59,12 +59,15 @@ obtained from this site also.
3. SQUASHFS FILESYSTEM DESIGN 3. SQUASHFS FILESYSTEM DESIGN
----------------------------- -----------------------------
A squashfs filesystem consists of a maximum of eight parts, packed together on a byte A squashfs filesystem consists of a maximum of nine parts, packed together on a
alignment: byte alignment:
--------------- ---------------
| superblock | | superblock |
|---------------| |---------------|
| compression |
| options |
|---------------|
| datablocks | | datablocks |
| & fragments | | & 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 written the completed inode, directory, fragment, export and uid/gid lookup
tables are written. 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 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 regular files and directories, and extended types where extra
information has to be stored. information has to be stored.
3.2 Directories 3.3 Directories
--------------- ---------------
Like inodes, directories are packed into compressed metadata blocks, stored 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 This scheme has the advantage that it doesn't require extra memory overhead
and doesn't require much extra storage on disk. 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 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 The index cache is designed to be memory efficient, and by default uses
16 KiB. 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 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 speed of access (and because it is small) is read at mount time and cached
in memory. 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 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 locate these. This second index table for speed of access (and because it
is small) is read at mount time and cached in memory. 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 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 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. 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 The xattr table contains extended attributes for each inode. The xattrs