Re: a question regarding Ext3 file truncate

["Xin Zhao" <uszhaoxin@gmail.com>]

Thanks a lot! I just found it.

If we need to truncate a file to 0 bytes, we have to change i_size to
0 first, then call ext3_truncate(). Then the code makes sense.

Xin

On 2/7/07, Mingming Cao <cmm@us.ibm.com> wrote:
> On Wed, 2007-02-07 at 12:16 -0500, Xin Zhao wrote:
> > Hi,
> >
> > Please forgive me if the question is dumb.
> >
> > I am modifying ext3 to add some new features, but was confused by the
> > implementation of ext3_truncate().
> >
> > In ext3_truncate():
> >
> > we first use
> >       n = ext3_block_to_path(inode, last_block, offsets, NULL);
> > to get the path of the last block.
> >
> > If the number of blocks is smaller than 12,  all blocks are then
> > direct blocks. We then need to clear them.
> >
> > But the interesting thing happens:
> >       if (n == 1)                                                                       /* direct blocks */
> >       {
> >               ext3_free_data(handle, inode, NULL, i_data+offsets[0],
> >                       i_data + EXT3_NDIR_BLOCKS);
> >               goto do_indirects;
> >       }
> > This code seems to free data blocks right after the blocks used by the
> > file. I think it should be
> > ext3_free_data(handle, inode, NULL, i_data, i_data+offsets[0]);
>
> Last_block is the last logical block after the truncate, so
> ext3_truncate() free data blocks after this point.
>
> Mingming
>
>