data blocks question

[Nehal]

On Wed, 29 Sep 2004 16:42:33 -0400
David Schultz <das at FreeBSD.ORG> wrote:

> On Wed, Sep 29, 2004, Nehal wrote:
> > on my ufs2 partition, there is a file that has a size of
> > 65536, and has 2 direct blocks only. the block size of the fs
> > is 16k and fragment block size is 2k.
> > 
> > how can this be possible? wouldn't 2 direct blocks mean that
> > the maximum size is 2x16k = 32k? or am i not understanding
> > something correctly?
> > 
> > i've made a copy of the file, and the new file has 4 direct
> > blocks.
> > 
> > it is a binary file, and i can read it fine (ie, cat it). i've
> > done fsck on the filesystem and it found no problem.
> 
> Yes, UFS supports sparse files.  That is, you can have a file
> with parts you haven't written to, and the blocks for those
> parts won't be allocated.  The cp utility doesn't know about
> this, though, so copies will have the ``holes'' filled with
> zeroes.
> 

how would i determine the offset and length of these 'holes' for
sparse files?

Nehal