Re: Access content of file via inodes

[Jeffrey Mahoney <jeffm@suse.com>]

Anton Altaparmakov wrote:
> Jeff Mahoney wrote:
> 
>>Kathy KN (HK) wrote:
>>
>>>What I meant by via blocks is to gain knowledge of the physical
>>>blocks used by the inodes and retrieve the content from it directly,
>>>by accessing b_data.
>>
>>The problem with that approach is that some filesystems may store part
>>of the file outside of a complete block. For example, reiserfs "tails"
>>will respond with -ENOENT on ->bmap. For files smaller than 16k, they
>>are quite common.
> 
> 
> This is one not true and two wrong!
> 
> Looking at reiserfs code in the current 2.6 kernel it does:
[...]
> This will result in sparse blocks being returned whenever an error
> occurs.  Not what is desired...
> 
> <rant>
> The problem with ->bmap is that it cannot return error at all.  It
> either returns 0 for sparse or >0 for real block.  ->bmap is the most
> stupid interface I have ever seen...  )-:  If you ask me it should be
> removed from the kernel without notice.  Let all applications that use
> it break.  Who cares...  It can always be replaced with a sensible
> interface that returns errors like -ESPARSE, -ENOTAPPLICABLE, -EIO,
> -ENOMEM, etc and doesn't assume that 0 is sparse...
> </rant>

Ugh. Mea culpa. I knew reiserfs_bmap would return less than useful
results, and stopped there. I should have dug a little deeper.

-Jeff

-- 
Jeff Mahoney
SuSE Labs
jeffm@suse.com