On Sat, Oct 29, 2011 at 6:03 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? >
problem is what u see as free blocks may not be seen at the kernel level as free block.....since u not holding any locks, there may be situation when your block allocation may conflict with that of the kernel, then u will get disastrous irrecoverable errors - worst case is your userspace data get overwritten by kernel. i supposed it is a legacy program, but there exists a small probability that this problem will occur. > >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 > -- Regards, Peter Teoh _______________________________________________ Kernelnewbies mailing list [email protected] http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
