UFS2 Group Descriptor
The UFS2 group descriptor has the same basic concepts as the UFS1 version, but some of its fields are larger. Its location relative to the start of the cylinder group is given in the superblock, and its location does not stagger like the UFS1 group descriptor does. The UFS2 version has the fields given in Table 17.6.
|
Byte Range |
Description |
Essential |
|---|---|---|
|
03 |
Unused |
No |
|
47 |
Magic signature (0x090255) |
No |
|
811 |
Unused |
No |
|
1215 |
Group number |
No |
|
1619 |
Unused |
No |
|
2023 |
Number of fragments in group |
No |
|
2427 |
Number of directories |
No |
|
2831 |
Number of free blocks |
No |
|
3235 |
Number of free inodes |
No |
|
3639 |
Number of free fragments (partial blocks) |
No |
|
4043 |
Last block allocated |
No |
|
4447 |
Last fragment allocated |
No |
|
4851 |
Last inode allocated |
No |
|
5283 |
Summary of available fragments |
No |
|
8491 |
Unused |
No |
|
9295 |
Inode bitmap (byte offset) |
Yes |
|
9699 |
Fragment bitmap (byte offset) |
Yes |
|
100103 |
Next available space in descriptor (byte offset) |
No |
|
104107 |
Counts of available clusters (consecutive blocks) (byte offset) |
No |
|
108111 |
Block bitmap (byte offset) |
No |
|
112115 |
Number of blocks in group |
No |
|
116119 |
Number of inodes in group |
No |
|
120 123 |
Last initialized inode |
No |
|
124135 |
Unused |
No |
|
136143 |
Last written time |
No |
|
144167 |
Unused |
No |
|
168+ |
Bitmaps and so on |
Yes |
Notice that in both versions, the only essential information is the offsets to the inode and fragment bitmaps. The bitmaps are located after byte 168, but still inside the block allocated to the group descriptor.