Re: dhcp vendor-option and grub net_pxe_extensionspath

[Carl Karsten]

On Fri, Apr 28, 2017 at 11:28 AM, Andrei Borzenkov <address@hidden>
wrote:

> 28.04.2017 08:57, Carl Karsten пишет:
> > I am using dnsmasq, but I can bring up isc dhcp too.  I need help with
> both
> > sides, but on the grub list I won't be too picky about what dhcp server
> is
> > used.
> >
> > I am looking for the syntax of dhcp vendor options, and then how to
> access
> > them in grub-net.  I think.  maybe there is a better way.
> >
> > I pxe boot grub, which boots di (Debian Installer) and pass a preseed
> file.
> >
> > I am trying to work out a nice way to pass host specific info to di
> > example, most use:
> > partman-auto/disk="/dev/sda"
> > but one machine has an onboard ssd nvme which needs /dev/nvme0n1
> >
> > di will read values appended to the kernel boot line, so I can hard code
> it
> > like this:
> >
> > menuentry "Install Ubuntu preseed" {
> > set gfxpayload=keep
> > linux /ubuntu-installer/amd64/linux gfxpayload=800x600x16,800x600 ---
> > auto=true url=dc10b hostname= partman-auto/disk="/dev/nvme0n1"
> > interface=${net_default_mac}
> > initrd /ubuntu-installer/amd64/initrd.gz
> > }
> >
> > interface=${net_default_mac} - use the nic that pxe booted.
> >
> > Now I get lost in conf options and syntax.  forgive me for making stuff
> up
> > here, if it worked I wouldn't be asking for help.
> >
> > I am hoping for something like
> > partman-auto/disk=$(net_pxe_extensionspath/disk}
> >
> > in dnsmasq conf:
> > dhcp-host=40:8d:5c:7f:bb:90,,gator
> >
> > dhcp-option-force=host:gator,209,"disk=/dev/nvme0n1"
> >
> > So yeah, how do I send random strings based on mac/hostname
> > and how do I read what was sent in grub?
> >
>
> You can use net_get_dhcp_option to extract from DHCP ACK packet. In this
> case it would be something like
>
> net_get_dhcp_option disk ${net_default_interface} 209 string
>
> Unless you intend to set multiple values in single option, setting its
> value to just "/dev/nvme0n1" simplifies further parsing.
>

This looks like the answer I am looking for.  Now to digest it.  This is on
the edge of what I am familiar with, so allow me to confirm things.

209 is how I reference the value I set?
Kinda like server sets key #209 = abc,
client says var = get key #209


Multiple values is something I should probably accommodate.

I am thinking

menuentry "Install Ubuntu preseed" {
set gfxpayload=keep
linux /ubuntu-installer/amd64/linux gfxpayload=800x600x16,800x600 ---
auto=true url=dc10b hostname=  interface=${net_default_mac} ${more_appends}
initrd /ubuntu-installer/amd64/initrd.gz
}

dhcp can supply
partman-auto/disk="/dev/nvme0n1"  user=foo pw_hash=abc
tasks="ubuntu-desktop"

either as one big value or a bunch of separate ones that get assembled.