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| -rw-r--r-- | Documentation/filesystems/squashfs.txt | 28 |
1 files changed, 19 insertions, 9 deletions
diff --git a/Documentation/filesystems/squashfs.txt b/Documentation/filesystems/squashfs.txt index 66699afd66ca..2d78f1911844 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 |