Hi Mike, > > I'm updating a user space program that finds free blocks on a ext2/3 > filesystem so that it works with ext4. I'm concerned about how extents > might affect my program. My program currently looks only at the block > allocation bitmaps. Are the block allocation bitmaps still updated when an > extent is created? > > >> AFAIK block allocations bitmaps are sufficient to give you information > related to block allocations, inode with extents should not > >> make any difference because extents are just to make block reading > efficient and can be used to represent a much bigger FS. > > >From what I can tell, extent information is only stored in the inode, and > is only a way to improve the efficiency of the process of creating the > structure needed in the inode. But I haven't been able to find out > anything about whether the block allocation bitmap is updated at the same > time. > > >> As part of extent inode allocation block bitmaps are updated for eg. > you can refer to > >> ext4_map_blocks > >> ext4_ext_map_blocks ( Only called if inode has extents ) > >> ext4_free_blocks > >> ext4_read_block_bitmap > > Regards, > Piyush > > On Sat, Oct 29, 2011 at 3:33 AM, Mike Gibson <[email protected] > > wrote: > >> I'm updating a user space program that finds free blocks on a ext2/3 >> filesystem so that it works with ext4. I'm concerned about how extents >> might affect my program. My program currently looks only at the block >> allocation bitmaps. Are the block allocation bitmaps still updated when an >> extent is created? >> >> >From what I can tell, extent information is only stored in the inode, >> and is only a way to improve the efficiency of the process of creating the >> structure needed in the inode. But I haven't been able to find out >> anything about whether the block allocation bitmap is updated at the same >> time. >> >> Do extents provide a new way of expressing which blocks are allocated on >> disk? Or are the block allocation bitmaps still the canonical way to >> determine if a given block is in use? >> >> Mike Gibson >> _______________________________________________ >> Kernelnewbies mailing list >> [email protected] >> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies >> > >
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