Re: [9front]

[thinktankworkspaces@gmail.com]

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Simply brilliant. I need to save this email somewhere and remember this logic. But honestly I'm 
tired of qemu. I really need to read up on how the booatloader works and how to bootstrap an
AWS ec2 instance. I never used 'xd' command before so thats interesting. There seems to be
some sort of syntatical magic here in plan9 thats missing in other OS's

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From: Eckard Brauer <eckard.brauer@gmx.de>
To: 9front@9front.org
Subject: Re: [9front]
Date: Wed, 12 Jan 2022 10:29:48 +0100
Message-ID: <20220112102948.4a6d7d53@gmx.de>

>  [...]
>
> Since you dd'd the iso to the usb drive before you can also just dd
> that amount of data back to an image file. I don't exactly know the
> parameter now, but the man page lists it.
>
>  [...]

As long as you're on P9, that should work:

dd -if /dev/sdXXX/disk -of outfile.iso -bs 4k -count 8192k

as long as the product of bs and count args are exactly the 32 GB. With
Unix/linux/bsd it should be the same, except that args are as in MVS
(if=/dev/sdY of=outfile.iso etc.).

Problem could be that the initial dd when preparing the usb went to the
(1st?) partition of the USB instead of the raw (whole) device. Maybe
it's possible to read&compare the first few bytes, e.g.

dd -if /dev/sdXXX -bs 1b -count 1 | xd -1x

the same for image.iso

> The sdUxxx directory contails lots of files for lowlevel interaction.
> E.g it contains a ctl and data, and a file for each partition you can
> mount.
>
> In this case I'm pretty sure you can call the command on the data
> file (which is the disk ignoring all partitions).
>
>  [...]
>
> 9front has its own bootloader, at least for x86/amd64 standard
> machines. However, some people got 9front booting with other linux
> bootloaders.

correct, but IMO that works like:

BIOS -> "other bootloader" -> 9pc/9pc64 -> plan9 kernel

where the 9pc/9pc64 plan9 bootloader still needs to be in a given
position or to be contiguous on disk - refer "bootloader magic" or the
like somewhere in the fqa.

But didn't try that with qemu at all, IIRC that was the init. problem.

>  [...]
>
> Have you tried dding the iso to a usb drive and edit the file in the
> fat directory? (And dding back)
>
> It might even be possible that you can mount the iso somehow and
> change the file there. I'm not sure about it and I don't know how it
> handles the mbr then...

For little edits NOT violating block boundaries, even in-binary-edits
are fine, did that a few time using sed, but you have to double
(triple,...) check the boundaries before. Or you could even split the
image file apart (with dd) into prefix + file contents + suffix, edit
the 2nd one, compare size and reassemble, if it's contiguous - but all
that's bit dangerous.