Syslinux - Mar 2003 - PXElinux question - not in FAQ (additional DHCP options)

Woody Suwalski <woody at suwalski.net> schrieb am 07.03.03
17:57:26:
> 
> Peter, we have met in Cyber space looong time ago, when I was requesting 
> 10:minor numbers for the Netwinder project....
> 
> Now I am trying to build a network boot for Xandros distribution.
> 
> I have it working, however I need to do 2 DHCP cycles - 1 happens in 
> PXE, and then it repeats in my network boot code (based on BusyBox). All 
> I need in the second stage is the NFS image address, passed by DHCP as
>     option root-path "dell:/XandrosInstallCD";
> 
> I could modify DHCP to use option vendor-encapsulated-options instead. 
> Is this one "eaten" by PXE firmware? What for is it in the first
place?
> 
> Would be nice if PXE linux could pass on the kernel command line other 
> vars similar to IPAPPEND info, but from your code  it looks that 
> pxelinux is not parsing other DHCP options...
> 
> Unless I could use your PXELINUX_MAGIC option. Since I do not need extra 
> config files, I could use the field to specify NFS root. But how to pass 
> it later to the kernel?
> 
> Thanks, Woody
> 
> 
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Woody Suwalski <woody at suwalski.net> schrieb am 07.03.03
17:57:26:
> 
> Peter, we have met in Cyber space looong time ago, when I was requesting 
> 10:minor numbers for the Netwinder project....
> 
> Now I am trying to build a network boot for Xandros distribution.
> 
> I have it working, however I need to do 2 DHCP cycles - 1 happens in 
> PXE, and then it repeats in my network boot code (based on BusyBox). All 
> I need in the second stage is the NFS image address, passed by DHCP as
>     option root-path "dell:/XandrosInstallCD";
> 
> I could modify DHCP to use option vendor-encapsulated-options instead. 
> Is this one "eaten" by PXE firmware? What for is it in the first
place?
> 
> Would be nice if PXE linux could pass on the kernel command line other 
> vars similar to IPAPPEND info, but from your code  it looks that 
> pxelinux is not parsing other DHCP options...
> 
> Unless I could use your PXELINUX_MAGIC option. Since I do not need extra 
> config files, I could use the field to specify NFS root. But how to pass 
> it later to the kernel?
> 
> Thanks, Woody
> 
> 
> _______________________________________________
> SYSLINUX mailing list
> Submissions to SYSLINUX at zytor.com
> Unsubscribe or set options at:
> http://www.zytor.com/mailman/listinfo/syslinux
> Please do not send private replies to mailing list traffic.
> 

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Hi,

sorry if you got this mail  without contents - seems that return sends the mail
here ...

Woody Suwalski <woody at suwalski.net> schrieb am 07.03.03
17:57:26:
> Now I am trying to build a network boot for Xandros distribution.
> 
> I have it working, however I need to do 2 DHCP cycles - 1 happens in 
> PXE, and then it repeats in my network boot code (based on BusyBox). All 
> I need in the second stage is the NFS image address, passed by DHCP as
>     option root-path "dell:/XandrosInstallCD";
It seems that you could just define this, without any changes.

pxelinux needs the server address and the boot file options
(DHCP options 66 & 67, ISC dhcp options next-server and filename),
and doesn't interest in the root-path option.

Did you already try this? Since it seems that you already did this without
success: Does your second DHCP request ask for the root-path option,
and did the server give it to the client? DHCP has a mechanism where the
client specifies which options it wants from the server, and the server
in turn responds with the defined options for this client. More on this is in
the various DHCP RFCs. AFAIK ethereal (or even tcpdump?) reports which 
options were requested by the client.
> Unless I could use your PXELINUX_MAGIC option. Since I do not need extra 
> config files, I could use the field to specify NFS root. But how to pass 
> it later to the kernel?
Give every client an own config file, and let these have something like

default bla
label bla
  kernel mykernel
  append root-path=<root path of this client> [further client-specific
options]

in this file. With this workaround every client would get its specific
kernel parameters, and these would be interpreted by the boot 
process (initrd, init-scripts or else). You could generate these by a script,
getting the data from one central source.

Regards,

Josef

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