Re: [Libcdio-devel] [PATCH 2/2] Add processing of Rock Ridge CE records

[Thomas Schmitt]

Hi,

Pete Batard wrote:
> Use the processed cont_extent to read the relevant continuation block
> into a buffer and then use that block, along with cont_offset and
> cont_size, to carry out further Rock Ridge data processing.
> [...]
> +       if (iso9660_iso_seek_read(p_image, buffer, cont_extent, 1) != 
> ISO_BLOCKSIZE)
> +         goto out;
> +       chr = &buffer[cont_offset];
> +       len = cont_size;

Do i get it right that encountering a CE entry causes immediate
continuation of interpretation at the depicted continuation area ?

If so, then this does not obey the specs. SUSP 1.12 says:

  The "CE" System Use Entry indicates a Continuation Area that shall be
  processed after the current System Use field or Continuation Area is
  processed.

So the CE parameters cont_extent, cont_offset, cont_size need to be
buffered until the while-loop has ended. Only then the continuation
area should be loaded and interpreted.

Linux and libisofs do this buffering when interpreting CE. GRUB does not.

mkisofs, genisoimage, and libisofs write CE as last entry, so that GRUB
did not experience problems yet. (I plan to craft a demonstration ISO
and to submit a patch to GRUB.)

--------------------------------------------------------------------
Further:

Consider to implement interpretation of the ST entry, which marks the
end of the SUSP data within a directory record or continuation area.
I.e. it should break the while-loop regardless of the remaining len.

SUSP 1.12 says

  If the remaining allocated space following the last recorded System
  Use Entry in a System Use field or Continuation Area is less than four
  bytes long, it cannot contain a System Use Entry and shall be ignored.
  Otherwise an "ST" System Use Entry (see section 5.4) shall be the last
  System Use Entry recorded in a System Use field or Continuation Area.

So the current while-loop condition

    while (len > 1){ /* There may be one byte for padding somewhere */

could be widened to (len >= 4) ... if i am not off by one.


Have a nice day :)

Thomas