[syslinux] isohybrid has 2 variants

Ady
Tue, 24 Jun 2014 20:56:06 -0000

> Hi,
>
> > For instance, if a common user reads a section about a general
> > concept, then introducing commands of specific tools (even with the
> > intention of clarity) could make the reader (mis)understand that such
> > tool or such commands are part of the general concept.
>
> The first example with "xorriso ... -isohybrid-mbr" serves the
> purpose to explain how the isohybrid feature can already
> by applied at ISO generation time.
>
> The second one with "genisoimage ... -e" is a necessary
precondition
> for the run of isohybrid --uefi.
>
>
> > Regarding current versions of the 3 tools built with cygwin, I only
> > know of mkisofs.
>
> I know from user feedback that GNU xorriso gets built on cygwin
> without problems.
>
>
> > For instance, should the _isohybrid_
> > wiki page in Syslinux include details about ISO9660 or FAT or MBR or
> > partition tables?
>
> I'd say no.
> But it has to be mentioned that isohybrid is about adding an MBR.
> It is necessary to know that for --uefi the ISO image has to contain
> an EFI boot image, which is supposed to be a FAT filesystem.
> It should also be mentioned that the boot path for UEFI is not
> only El Torito and GPT but also a partition entry in MBR.
>
> That's just the immediate interfaces which isohybrid needs as input
> or provides as output.
>
>
> >  http://cdrecord.org/
>
> Ah yes.
>
>
> > > If you see particular statements which are surplus under this
> > > aspect, then we can discuss and eventually throw them out.
>
> > IMHO (not a strict list):
>
> Urm. That is a list of new topics, not of surplus statements in
> my proposals.
>
>
> > _ basic general concept, relevant for common user (one paragraph,
> > something about "image bootable in optical media and USB
drives");
>
> I thought to have provided this in my proposal.
> A motivation in the first two statements and then a quick tour with
> several key terms and concepts.
>
>
> > _ general "pros/cons" relevant for common users: the USB
drive is
> > overwritten, with one non-writable filesystem, part of the USB drive
> > is not being used/seen;
>
> Yes. The whole discussion is still missing about suitable storage
> media and how to put the image onto them.
>
>
> > _ different variants exist, which ones are those variants;
>
> Three of them are presented in the BIOS paragraph. One of them
> is not mentioned in UEFI because not capable of it.
>
>
> > _ requirements and limitations: matching version with ISOLINUX in the
> > ISO image, Perl OS-independent, based on C is OS (Linux) -dependent,
> > possibility to produce images bootable in UEFI systems,...;
>
> This is mentioned for the both SYSLINUX tools. See bullet list.
> xorriso dependencies and installation is not really in the scope of
> the wiki. (I'd blatantly advertise GNU xorriso if i am invited to do.)
>
>
> > _ respective command options for isohybrid variants, specially those
> > included in Syslinux,
>
> That would be the job of a man page.
> One could start with the quickly-made one from Ubuntu
>   http://manpages.ubuntu.com/manpages/natty/man1/isohybrid.1.html
>
> With -h or -s we get to the same undecidable discussions about
> cylinder size which we had a while ago. We did not really make
> progress with getting this well documented.
> -e , -t, -i are MBR specific.
> -o is a bit questionable, as a non-zero value will normally make
> the partition unmountable.
> --forcehd0, --ctrlhd0, --partok choose the built-in MBR template.
>
> They all need exploration and lots of background information.
>
>
> > _ basic examples;
>
> I claim that
>
>   isohybrid output.iso
>
>   isohybrid --uefi output.iso
>
> are basic.
>
>
> > _ resources, see also, more info...
>
> I take proposals.
>
>
> >  http://www.syslinux.org/wiki/index.php/Mbr
>
> Ahum. This this suggests that "hd0" in "--forcehd0" and
"--ctrlhd0"
> are about BIOS disk 0x80 and suffixes "_f" and "_c".
> "--partok" would then select a flavour of "altmbr.bin"
rather than
> one of "mbr.bin".
>
> From section "Write" one could derive instructions about how
> to put the image onto an USB stick by help of Linux.
>
> Probably the article should have a short introduction into
> the concept of MBR.
> I put a link to it into my proposal (if the captcha thing lets me).
>
>
> > > > _ The firmware "target(s)" can be different than
the one used by the
> > > > host where the ISOLINUX and/or isohybrid image is being
built.
> > > Now you lost me.
> > A user could be building an image so to be bootable in UEFI systems
> > (too), but he is building such image in a BIOS system.
>
> Do we really have to explain that the firmware is not of importance
> after the operating system has booted ?
>
>
> > My point is, the options ("-u", "-m",
"-b"...) are for the "target"
> > system(s), and (at least some) combinations are allowed.
>
> This is indeed worth to be mentioned.
> But it is not really specific to isohybrid, but rather to
> the question what interfaces and early stage software has to
> be offered to the intended boot firmware.
> More or less the overall topic of SYSLINUX et.al.
>
>
> > As one of Didier's questions suggests, the _alternative_ methods
seem
> > to be not clear enough.
>
> I am pondering about a translation table from isohybrid options
> to isohdp[fp]x*.bin and the terminology in the Mbr article.
> (Three terminologies for the same thing. Sometimes, choice is bad.)
>
>
> > > I showed three of the variants: isohybrid.pl, isohybrid.c,
xorriso.
> > > The other two are not clear enough to me.
>
> > Do you mean from Slitaz?
>
> Yep. The .sh script and the .c program which both seem to perform
> isohybrid for BIOS. But i did not analyze them in detail.
>
>
> > -eltorito-platform 0xEF \
>
> Now added to the UEFI section. (More example code, of course. Maybe
> it should be presented without ... .)
>
>
> Have a nice day :)
>
> Thomas
>

@Thomas,

Reading forum posts and the like, common users most frequently don't
care about FAT, MBR, GPT, UEFI... The whole point of isohybrid is to
try to simplify "burning" an ISO image to a (USB) drive. Users
frequently want to know "step #1: do this, step #2 do that, step #3
reboot". Users with more experience / knowledge would probably avoid
isohybrid for their own use, and install SYSLINUX/EXTLINUX instead.

Regarding xorriso in cygwin... If someone has built xorriso under
cygwin for his own use, good for them. Please forgive me for
mentioning this yet again: common users. If there is a trustworthy
site providing current versions of xorriso binaries built under
cygwin, they are unknown to me. There is more than one site with
cdrtools / mkisofs binaries built under cygwin, and at least one
(which I consider trustworthy) maintaining updates for each new
(alpha) release of cdrtools / mkisofs. That doesn't make it better
than others; just available (for common users).

I just posted comments as requested. They have no more value than
others. Please go ahead and do what you think it's appropriate.

Thank you,
Ady.

PS: If you want/need to, for a list of pages in the wiki, use
"special pages" -> "all pages". There are more than 100
(certainly
not all up-to-date).