Creating code slice before disk image in nanobsd

[Arrigo Marchiori]

Hello list,

to answer some of Warren's questions, I will describe what the patch
currently does.

I am not a gpart expert, so you can propose your own considerations and
fixes if you know the subject.

On Wed, Jan 15, 2014 at 12:50:33PM -0700, Warren Block wrote:

> On Thu, 16 Jan 2014, Ian Smith wrote:
> 
> > On Wed, 15 Jan 2014 07:53:08 -0700, Warner Losh wrote:
> >
> > > I'll take a look at things... It isn't obvious at first blush this is
> > > the right thing to do, but I need to think about it a bit...
> > >
> > > Warner
> >
> > Perhaps an aside, but I'm pretty sure Warren (cc'd) has said that gpart
> > can do anything that fdisk AND bsdlabel can do?
> 
> Yes.  Although there is an exception: gpart silently forces alignment to 
> CHS values on MBR slices, and fdisk does not.  So to get a 4K-aligned 
> slice requires fdisk.  gpart can align BSD partitions inside a slice to 
> 4K, but that is a workaround.  (I believe gpart should default to CHS 
> but use -a alignment or -b values when given for MBR slices, regardless 
> of the MBR spec.  This becomes increasingly important as 4K drives and 
> SSDs become more common.)

I didn't take alignment into account; I just adapted the calculations
to match the parameters required by gpart.

> >  If that's so, and the
> > object here is to deprecate fdisk, why not also replace these lines:
> >
> > +
> > +	bsdlabel -w -B -b ${NANO_WORLDDIR}/boot/boot ${MD}
> > +	bsdlabel ${MD}
> > +
> >
> > with their gpart equivalents?
> >
> > (and no, I don't know what those should be in this context)
> 
> To create the initial MBR, probably already done before the code above:
>    gpart create -s mbr ${MD}

This is done by the patch.

[...]
> To create a slice and set it active:
>    gpart add -s freebsd ${MD}    [1]
[...]
> [1] when creating the slice, -a4k or -b1m can be specified but will be
>      silently rounded to CHS values

The -b parameter is also used, therefore your note [1] applies.

>    gpart set -a active -i1 ${MD}

This is done by the patch.

> To create the BSDlabel inside the slice and write the bootcode to it:
>    gpart create -s bsd ${MD}s1
>    gpart bootcode -b ${NANO_WORLDDIR}/boot/boot ${MD}s1
> Then BSD partitions can be added with, for example:
>    gpart add -t freebsd-ufs -s2g ${MD}s1  [2]
[...]
> [2] when creating BSD partitions, -a4k can be used and they will be
>      created with an offset inside the slice to end up aligned

These were kept as the original:

bsdlabel -w -B -b ${NANO_WORLDDIR}/boot/boot ${MD}s1

> For reference, see 
> http://www.wonkity.com/~wblock/docs/html/disksetup.html#_the_old_standard_mbr

Regards,
-- 
rigo

http://rigo.altervista.org