ext4 extents

[piyush moghe]

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 <mike.gibson at storagecraft.com
> > 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
>> Kernelnewbies at kernelnewbies.org
>> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>>
>
>
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