When is a block free?

Ric Wheeler rwheeler at redhat.com
Tue Sep 16 20:17:12 UTC 2008

Chris Worley wrote:
> Where in the ext2/3 code does it know that a block on the disk is now 
> free to reuse?
> Thanks,
> Chris
Hi Chris,

File systems track which blocks are free from the file system creation 
time (mkfs), creation of new files and deletion. Ext2/3 is the 
gatekeeper for all deletions, so it knows when file system blocks 
transition from the used state to the free state. Ext file system use 
bitmaps to track the blocks that are allocated or not.



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