README
1
2This is a little C-program that can be used to print out the list
3of blocks used by a requested list of inodes.
4
5For example, to list the blocks referenced by your kernel:
6
7guest_12 % df /
8Filesystem 1K-blocks Used Avail Capacity Mounted on
9/dev/gpt/rootfs 20307196 10707336 7975288 57% /
10
11guest_12 % ls -i /boot/kernel/kernel
12160603 /boot/kernel/kernel
13
14guest_12 % ./prtblknos /dev/gpt/rootfs 160603
15160603: lbn 0-7 blkno 3217584-3217647
16 lbn 8-11 blkno 3217864-3217895 distance 216
17First-level indirect, blkno 3217896-3217903 distance 0
18 lbn 12-19 blkno 3217904-3217967 distance 8
19 lbn 20-75 blkno 3251816-3252263 distance 33848
20 lbn 76-83 blkno 3252368-3252431 distance 104
21 lbn 84-91 blkno 3252464-3252527 distance 32
22 lbn 92-852 blkno 3252896-3258983 distance 368
23
24Each contiguous range of blocks is printed on a line.
25The distance metric is the size of the gap from the end of the
26previous set of blocks to the beginning of the next set of blocks.
27Short distances are desirable.
28
29The logical block numbers (lbn above) describe filesystem-block
30size blocks which by today's default is 32Kb.
31
32The physical block numbers (blkno above) describe the smallest piece
33of disk space that an inode can reference which is a filesystem
34fragment. Since the default size for fragments today is 4Kb, the
35physical block numbers reference 4Kb blocks. The distances listed
36above are also in physical block size units. Thus a distance of 8
37means a separation of just one 32Kb block. For example lbn 11, ends
38at 3217895, the 32Kb first level indirect immediately follows it at
393217896-3217903, and lbn 12 starts distance 8 after lbn 11 immediately
40after the indirect block at 3217904.
41
42If you were to create a filesystem with the fragment size equal to
43half the block size (say 32Kb blocks with 16Kb fragments) then the
44physical block numbers listed would be 16Kb in size.
45
46 Marshall Kirk McKusick
47 January 19, 2018
48