Re: dhcp vendor-option and grub net_pxe_extensionspath

[Carl Karsten]

On Apr 28, 2017 2:32 PM, "Andrei Borzenkov" <address@hidden> wrote:

28.04.2017 21:13, Carl Karsten пишет:
> 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
>

Yes. This is option number.

>
> 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.
>

Well, you will then probably need regex command to extract individual
values. Allocating DHCP option number for each individual value
certainly makes it easier.


For now I am happy with one big string in and one big string out.  The
kernel or installer will parse it.

But of I do need to send individual values, what option numbers are
available?