DragonflyBSD GEOM? (Re: Is it time to dump disklabel and use GPT instead?)

Matthew Dillon dillon at apollo.backplane.com
Thu Jul 29 18:04:48 PDT 2010

:>     If someone wants to write a really nice gpt partition editor that
:>     pops you into vi or emacs or whatever then I would be more amendable
:>     to using gpt as a default.  But if all we have is command-line
:>     list/add/remove junk, then no.
:Can you give me some pointers as for where to start looking for more
:information on our implementation of GPT? How much low level stuff is
:involved in writing such an editor?

    The kernel understands gpt partitions.  The boot code does not.
    The userland tools are the old FreeBSD tools, in /usr/src/sbin/gpt.

    GPT based projects can be broken down as follows:

    For the gpt tool:

	* Add an editor feature to the gpt tool that lays out existing
	  partitions and allows new ones to be specified, similar to
	  how disklabel -e works now.

	* Implement super sector alignment and implement silent skipping
	  of the small gap areas created between partitions when super sector
	  alignment is done.

    For the boot code:

	gpt with a compat mbr replaces fdisk entirely.  Add a version of
	the boot0 code that can find the boot partition.  Another option
	here is to hardwire the offset in and have gpt figure it out and
	update it in-place, which might be needed for boot0.

	A gtp-aware boot1/boot2 is then needed, and probably also a
	gpt-aware loader.

	I expect a good chunk of this could be ported from FreeBSD.

    For native GPT booting (non compat MBR booting) ... I don't know much
    about that, but it would be a separate sub-project.

					Matthew Dillon 
					<dillon at backplane.com>

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