PXE boot

[John Baldwin]

On Wednesday, September 03, 2014 04:12:01 PM Sinha, Prokash wrote:
> Hi All,
> 
> I'm trying to understand the invocation of the routines pxe_init();
> pxe_open()   etc.  in pxe.c
> 
> By the structure, it looks like a driver with devsw_pxedisk = { entry points
> …}
> 
> Once this pxeldr is brought down from the net boot server, how does it get
> invoked ( or rather who calls these routines ) ??? The loader ( strapped
> with it don't seem to call).
> 
> I assume that the the boot code in the NVRAM ( or wherever ) of the NIC that
> supports calls these pxe_* () functions ???

pxeboot is pxeldr + /boot/loader.  The firmware (BIOS or EFI) downloads the 
pxeboot binary to a known fixed address and starts executing it.  When it 
starts executing, pxeldr finds the /boot/loader binary "behind" it and 
arranges for it to run.  It passes a flag telling it that it was booted via 
PXE.  The loader then uses the routines in pxe.c to talk to firmware on the 
NIC.  The firmware provides both TFTP and UDP interfaces.  The loader uses 
those to provide either a TFTP "filesystem" or to mount an NFS filesystem over 
UDP.

-- 
John Baldwin