Re: [Libcdio-devel] Re: can files in UDF be fragmented?

[Rocky Bernstein]

On Sat, Oct 23, 2010 at 7:03 AM, Thomas Schmitt <address@hidden> wrote:

> Hi,
>
> i have to correct myself. In previous mail i wrote:
>
> > Quite helpful is  udf_file_entry_[ts].i_alloc_descs  which i
> > recognize from ECMA-167 as the extent counter.
> > So all is well if this is 1.
>
> The size is counted in bytes and not in descriptor records.
> So it is safe if udf_file_entry_t.i_alloc_descs is 8 or 20.
> It might be safe with 16, but then one needs to make sure it is
> a single "long_ad" and not two "short_ad".
>
> For the interpretation one would have to check:
>
>  udf_file_entry_t.icb_tag.flags & ICBTAG_FLAG_AD_MASK
>
> for ICBTAG_FLAG_AD_SHORT, ICBTAG_FLAG_AD_LONG, ...
>
> (I did not check whether all these symbols are public.


They are public.


> That approach is
>  educating for me, but unappealing for any user of the library.)
>

Yep. Based on what you report, it looks like udf_read_block has all the
information it needs to check. From udf_dirent_t, it could
get udf_file_entry_t.i_alloc_descs

However, since I don't have test UDFs to work against, I am not inclined to
pursue this further.


>
> ------------------------------------------------------------------------
>
>
> For the original topic of this thread:
>
> The extent size of "short_ad" is restricted to 1 GB - 1.
> So a reason for fragmentation might already be given if a file is 1 GB
> or larger.
>

That's a necessary reason but not the only reason. Another reason one finds
files with noncontiguous regions occurs after the file is modified.

>
>
> Have a nice day :)
>
> Thomas
>
>
>