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SubjectRe: ext4_fiemap gives 0 extents for files smaller than a block (patch included)
Leonard Michlmayr wrote:
> Thank you for your reply.
>
>>> @@ -3700,7 +3701,8 @@
>>> start_blk = start >> inode->i_sb->s_blocksize_bits;
>>> - len_blks = len >> inode->i_sb->s_blocksize_bits;
>>> + end_blk = (start + len - 1) >> inode->i_sb->s_blocksize_bits;
>>> + len_blks = end_blk - start_blk + 1;
>> I don't think this is quite correct either. For example, if blocksize
>> is 1024
>> and start is 1023 (start_blk = 0) and len is 2 (end = 1024, end_blk =
>> 1) then
>> len_blks = 2 which is too much.
>
> I think that len_blks = 2 is the correct value, because the requested
> region extends into 2 blocks (namely 0 and 1). If both blocks are in two
> separate extents, then ext4_ext_walk_space should report 2 extents. (If
> it's the same extent, only 1 will be reported anyways)
>
>> I think the right calculation here is:
>>
>> end_blk = (start + len + inode->i_sb->s_blocksize - 1) >>
>> inode->i_sb->s_blocksize_bits;
>> len_blks = end_blk - start_blk;
>>
>
> This is exactly the same (provided that len > 0). You can convince
> yourself easily that ((blocksize + x) >> blocksize_bits == x >>
> blocksize_bits + 1) for any positive x, because the lower bits of
> blocksize are all 0. (Your calculation would handle the case len == 0
> right, if that was allowed.)
>
> Regards
> Leonard

I was wondering if there is any update on the status of this patch.
Thanks !

Warm Regards,
Surbhi.




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