[syslinux] [PATCH] isohybrid: user options

[H. Peter Anvin]

Thomas Schmitt wrote:
> 
>> I *think* under Linux you can
>> mount such a partition with the option "sbsector=0", or Linux can
>> probably mount the raw device (/dev/sda as opposed to /dev/sda1).
> 
> On a media with no multiple logical tracks 
> -o sbsector=0 should have the same effect
> as mounting without sbsector option.
> So if the byte address space of /dev/sda1 does
> not start at media LBA 0, then sbsector=0 will
> not help.
> 

The normal superblock sector is 16.  However, looking through the code
it looks like the sbsector option actually refers to the *session* start
sector, not the superblock, which was the main thing:

        vol_desc_start = (opt.sbsector != -1) ?
                opt.sbsector : isofs_get_last_session(s,opt.session);

        for (iso_blknum = vol_desc_start+16;

The +16 is added later... I don't know if it would accept a negative
sbsector offset (other than -1, which is obviously used as a sentinel.)

> One could position the ISO image on media
> so that it actually has the matching offset
> without using it in its inner LBA addresses.
> (I.e. the image may *not* be made aware of
>  the offset by e.g. mkisofs option -C 0,offset)

I have no idea what you're trying to say here.  The real superblock has
to be at LBA 16 (and the boot record at LBA 17), otherwise it will not
boot when written to a real CD-ROM.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.