49 lines
1.9 KiB
Plaintext
49 lines
1.9 KiB
Plaintext
# $FreeBSD$
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This is a little C-program that can be used to print out the list
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of blocks used by a requested list of inodes.
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For example, to list the blocks referenced by your kernel:
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guest_12 % df /
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Filesystem 1K-blocks Used Avail Capacity Mounted on
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/dev/gpt/rootfs 20307196 10707336 7975288 57% /
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guest_12 % ls -i /boot/kernel/kernel
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160603 /boot/kernel/kernel
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guest_12 % ./prtblknos /dev/gpt/rootfs 160603
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160603: lbn 0-7 blkno 3217584-3217647
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lbn 8-11 blkno 3217864-3217895 distance 216
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First-level indirect, blkno 3217896-3217903 distance 0
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lbn 12-19 blkno 3217904-3217967 distance 8
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lbn 20-75 blkno 3251816-3252263 distance 33848
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lbn 76-83 blkno 3252368-3252431 distance 104
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lbn 84-91 blkno 3252464-3252527 distance 32
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lbn 92-852 blkno 3252896-3258983 distance 368
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Each contiguous range of blocks is printed on a line.
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The distance metric is the size of the gap from the end of the
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previous set of blocks to the beginning of the next set of blocks.
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Short distances are desirable.
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The logical block numbers (lbn above) describe filesystem-block
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size blocks which by today's default is 32Kb.
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The physical block numbers (blkno above) describe the smallest piece
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of disk space that an inode can reference which is a filesystem
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fragment. Since the default size for fragments today is 4Kb, the
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physical block numbers reference 4Kb blocks. The distances listed
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above are also in physical block size units. Thus a distance of 8
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means a separation of just one 32Kb block. For example lbn 11, ends
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at 3217895, the 32Kb first level indirect immediately follows it at
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3217896-3217903, and lbn 12 starts distance 8 after lbn 11 immediately
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after the indirect block at 3217904.
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If you were to create a filesystem with the fragment size equal to
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half the block size (say 32Kb blocks with 16Kb fragments) then the
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physical block numbers listed would be 16Kb in size.
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Marshall Kirk McKusick
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January 19, 2018
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