diff options
Diffstat (limited to 'Documentation/filesystems/squashfs.txt')
-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. | |||
59 | 3. SQUASHFS FILESYSTEM DESIGN | 59 | 3. SQUASHFS FILESYSTEM DESIGN |
60 | ----------------------------- | 60 | ----------------------------- |
61 | 61 | ||
62 | A squashfs filesystem consists of a maximum of eight parts, packed together on a byte | 62 | A squashfs filesystem consists of a maximum of nine parts, packed together on a |
63 | alignment: | 63 | byte 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 | |||
91 | written the completed inode, directory, fragment, export and uid/gid lookup | 94 | written the completed inode, directory, fragment, export and uid/gid lookup |
92 | tables are written. | 95 | tables are written. |
93 | 96 | ||
94 | 3.1 Inodes | 97 | 3.1 Compression options |
98 | ----------------------- | ||
99 | |||
100 | Compressors can optionally support compression specific options (e.g. | ||
101 | dictionary size). If non-default compression options have been used, then | ||
102 | these are stored here. | ||
103 | |||
104 | 3.2 Inodes | ||
95 | ---------- | 105 | ---------- |
96 | 106 | ||
97 | Metadata (inodes and directories) are compressed in 8Kbyte blocks. Each | 107 | Metadata (inodes and directories) are compressed in 8Kbyte blocks. Each |
@@ -114,7 +124,7 @@ directory inode are defined: inodes optimised for frequently occurring | |||
114 | regular files and directories, and extended types where extra | 124 | regular files and directories, and extended types where extra |
115 | information has to be stored. | 125 | information has to be stored. |
116 | 126 | ||
117 | 3.2 Directories | 127 | 3.3 Directories |
118 | --------------- | 128 | --------------- |
119 | 129 | ||
120 | Like inodes, directories are packed into compressed metadata blocks, stored | 130 | 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. | |||
144 | This scheme has the advantage that it doesn't require extra memory overhead | 154 | This scheme has the advantage that it doesn't require extra memory overhead |
145 | and doesn't require much extra storage on disk. | 155 | and doesn't require much extra storage on disk. |
146 | 156 | ||
147 | 3.3 File data | 157 | 3.4 File data |
148 | ------------- | 158 | ------------- |
149 | 159 | ||
150 | Regular files consist of a sequence of contiguous compressed blocks, and/or a | 160 | 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. | |||
163 | The index cache is designed to be memory efficient, and by default uses | 173 | The index cache is designed to be memory efficient, and by default uses |
164 | 16 KiB. | 174 | 16 KiB. |
165 | 175 | ||
166 | 3.4 Fragment lookup table | 176 | 3.5 Fragment lookup table |
167 | ------------------------- | 177 | ------------------------- |
168 | 178 | ||
169 | Regular files can contain a fragment index which is mapped to a fragment | 179 | 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 | |||
173 | speed of access (and because it is small) is read at mount time and cached | 183 | speed of access (and because it is small) is read at mount time and cached |
174 | in memory. | 184 | in memory. |
175 | 185 | ||
176 | 3.5 Uid/gid lookup table | 186 | 3.6 Uid/gid lookup table |
177 | ------------------------ | 187 | ------------------------ |
178 | 188 | ||
179 | For space efficiency regular files store uid and gid indexes, which are | 189 | 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 | |||
182 | locate these. This second index table for speed of access (and because it | 192 | locate these. This second index table for speed of access (and because it |
183 | is small) is read at mount time and cached in memory. | 193 | is small) is read at mount time and cached in memory. |
184 | 194 | ||
185 | 3.6 Export table | 195 | 3.7 Export table |
186 | ---------------- | 196 | ---------------- |
187 | 197 | ||
188 | To enable Squashfs filesystems to be exportable (via NFS etc.) filesystems | 198 | 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 | |||
196 | used to locate these. This second index table for speed of access (and because | 206 | used to locate these. This second index table for speed of access (and because |
197 | it is small) is read at mount time and cached in memory. | 207 | it is small) is read at mount time and cached in memory. |
198 | 208 | ||
199 | 3.7 Xattr table | 209 | 3.8 Xattr table |
200 | --------------- | 210 | --------------- |
201 | 211 | ||
202 | The xattr table contains extended attributes for each inode. The xattrs | 212 | The xattr table contains extended attributes for each inode. The xattrs |