Loading Documentation/filesystems/squashfs.txt +19 −9 Original line number Diff line number Diff line Loading @@ -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 | |---------------| Loading @@ -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 Loading @@ -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 Loading Loading @@ -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 Loading @@ -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 Loading @@ -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 Loading @@ -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 Loading @@ -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 Loading Loading
Documentation/filesystems/squashfs.txt +19 −9 Original line number Diff line number Diff line Loading @@ -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 | |---------------| Loading @@ -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 Loading @@ -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 Loading Loading @@ -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 Loading @@ -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 Loading @@ -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 Loading @@ -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 Loading @@ -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 Loading
Phillip Lougher <phillip@lougher.demon.co.uk>Phillip Lougher <phillip@lougher.demon.co.uk>