Enhancing cdboot [patch for review]

[Luigi Rizzo]

On Mon, Dec 08, 2008 at 02:40:41PM -0800, Maxim Sobolev wrote:
> Hi,
> 
> Below please find patch that enhances cdboot with two compile-time options:
...
> Any comments/suggestions are appreciated. If there are no objections I
> would like to commit the change. The long-term goal is to make
> CDBOOT_PROMPT default mode for installation CD.
> 
> http://sobomax.sippysoft.com/~sobomax/cdboot.diff

Looks good. Some comments:
1. since there is plenty of space in the cdboot sector, why don't you
   make the two option always compiled in, controlling which one to
   activate through flags in the bootsector itself, to be set
   patching the binary sector itself using a mechanism similar to
   boot0cfg.
      Of course you cannot alter a cdrom after you burn it,
   but it makes it easier to build CDs with one or the other defaults,
   patching cdboot or the iso image itself before creating/burning it.

2. in fact, the 'silent' option could be disabled at runtime by
   pressing some key (e.g. adding a short wait loop before proceeding;
   if this is meant for custom, unattended CDs the extra delay should not
   matter much);

3. one nitpick -- in one of the first chunks you replace $start
   with $LOAD, but if i am not mistaken operation depends on $LOAD = $start,
   so why don't you always use the same ?
     Also in terms of relocation size, wouldn't it be the case of
   hardwiring the size of the cd boot sector:

-       mov $((end_init - start)/2),%cx
+       mov 1024,%cx

4. another nitpick -- the value you pass in %si to the MBR does not
   seem to point to anything useful. As discussed about boot0.S and
   the followup in the mailing lists, there seems to be no standard
   but at least some MBR expect %si to point to a partition entry,
   so you should probably initialize one in a way similar way to that
   used by boot0.S

cheers
luigi