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-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 66699afd66ca..2d78f1911844 100644
--- a/Documentation/filesystems/squashfs.txt
+++ b/Documentation/filesystems/squashfs.txt
@@ -59,12 +59,15 @@ obtained from this site also.
593. SQUASHFS FILESYSTEM DESIGN 593. SQUASHFS FILESYSTEM DESIGN
60----------------------------- 60-----------------------------
61 61
62A squashfs filesystem consists of a maximum of eight parts, packed together on a byte 62A squashfs filesystem consists of a maximum of nine parts, packed together on a
63alignment: 63byte alignment:
64 64
65 --------------- 65 ---------------
66 | superblock | 66 | superblock |
67 |---------------| 67 |---------------|
68 | compression |
69 | options |
70 |---------------|
68 | datablocks | 71 | datablocks |
69 | & fragments | 72 | & fragments |
70 |---------------| 73 |---------------|
@@ -91,7 +94,14 @@ the source directory, and checked for duplicates. Once all file data has been
91written the completed inode, directory, fragment, export and uid/gid lookup 94written the completed inode, directory, fragment, export and uid/gid lookup
92tables are written. 95tables are written.
93 96
943.1 Inodes 973.1 Compression options
98-----------------------
99
100Compressors can optionally support compression specific options (e.g.
101dictionary size). If non-default compression options have been used, then
102these are stored here.
103
1043.2 Inodes
95---------- 105----------
96 106
97Metadata (inodes and directories) are compressed in 8Kbyte blocks. Each 107Metadata (inodes and directories) are compressed in 8Kbyte blocks. Each
@@ -114,7 +124,7 @@ directory inode are defined: inodes optimised for frequently occurring
114regular files and directories, and extended types where extra 124regular files and directories, and extended types where extra
115information has to be stored. 125information has to be stored.
116 126
1173.2 Directories 1273.3 Directories
118--------------- 128---------------
119 129
120Like inodes, directories are packed into compressed metadata blocks, stored 130Like 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.
144This scheme has the advantage that it doesn't require extra memory overhead 154This scheme has the advantage that it doesn't require extra memory overhead
145and doesn't require much extra storage on disk. 155and doesn't require much extra storage on disk.
146 156
1473.3 File data 1573.4 File data
148------------- 158-------------
149 159
150Regular files consist of a sequence of contiguous compressed blocks, and/or a 160Regular 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.
163The index cache is designed to be memory efficient, and by default uses 173The index cache is designed to be memory efficient, and by default uses
16416 KiB. 17416 KiB.
165 175
1663.4 Fragment lookup table 1763.5 Fragment lookup table
167------------------------- 177-------------------------
168 178
169Regular files can contain a fragment index which is mapped to a fragment 179Regular 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
173speed of access (and because it is small) is read at mount time and cached 183speed of access (and because it is small) is read at mount time and cached
174in memory. 184in memory.
175 185
1763.5 Uid/gid lookup table 1863.6 Uid/gid lookup table
177------------------------ 187------------------------
178 188
179For space efficiency regular files store uid and gid indexes, which are 189For 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
182locate these. This second index table for speed of access (and because it 192locate these. This second index table for speed of access (and because it
183is small) is read at mount time and cached in memory. 193is small) is read at mount time and cached in memory.
184 194
1853.6 Export table 1953.7 Export table
186---------------- 196----------------
187 197
188To enable Squashfs filesystems to be exportable (via NFS etc.) filesystems 198To 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
196used to locate these. This second index table for speed of access (and because 206used to locate these. This second index table for speed of access (and because
197it is small) is read at mount time and cached in memory. 207it is small) is read at mount time and cached in memory.
198 208
1993.7 Xattr table 2093.8 Xattr table
200--------------- 210---------------
201 211
202The xattr table contains extended attributes for each inode. The xattrs 212The xattr table contains extended attributes for each inode. The xattrs