PXE boot

[Sinha, Prokash]

On 9/4/14 9:31 AM, "Sinha, Prokash" <psinha at panasas.com> wrote:

>Thanks once again...
>
>This is the part - that you spelled out is why I had a trace in the
>pxe_enable(...) routine. As well as at pxe_init( ...) routine, just to be
>sure
>the pxe.c routines are working like ( as you said ) devsw invocation. But
>did not see the trace messages, could be serial console is not acting (
>though I doubt it).
>
>Now gave me a base, off of what I could debug ...
>
>-prokash
>
>On 9/4/14 7:57 AM, "John Baldwin" <jhb at freebsd.org> wrote:
>
>>On Wednesday, September 03, 2014 11:16:05 PM Sinha, Prokash wrote:
>>> Thanks much, John !
>>> 
>>> When it starts executing ? How ?. Who starts executing these. From the
>>> Makefile it's org is 0x7c00. So I would assume that it would be loaded
>>>at
>>> that absolute real-mode address !. I don't understand this part. But,
>>>if I
>>> put traces, I see pxe_open, and pxe_close are being called, but after
>>>all
>>> these pxe_calls are done, the loader's main is invoked at Rebooting Š
>>>time.
>>> 
>>> We are using a net boot server, and I see mountd- authenticated Š
>>>message
>>> storm on the boot server side.
>>> 
>>> Wondering what could cause such a message storm, while pxe_open() ->
>>>net
>>> if_open( ) executes.
>>
>>The PXE BIOS uses TFTP to fetch the pxeboot binary (and it will do its
>>own 
>>DHCP, etc. as part of doing that).  It writes the binary it downloads
>>starting 
>>at address 0x7c00.  Once the download is complete, it jumps to 0x7c00
>>similar 
>>to how booting from a disk loads the first sector at address 0x7c00 and
>>then 
>>jumps to it.
>>
>>The PXE calls in libi386 should not be invoked until the loader main()
>>routine 
>>runs:
>>
>>    /*
>>     * Special handling for PXE and CD booting.
>>     */
>>    if (kargs->bootinfo == 0) {
>>	/*
>>	 * We only want the PXE disk to try to init itself in the below
>>	 * walk through devsw if we actually booted off of PXE.
>>	 */
>>	if (kargs->bootflags & KARGS_FLAGS_PXE)
>>	    pxe_enable(kargs->pxeinfo ? PTOV(kargs->pxeinfo) : NULL);
>>	else if (kargs->bootflags & KARGS_FLAGS_CD)
>>	    bc_add(initial_bootdev);
>>    }
>>
>>That enables the PXE devsw driver so that it will do something later when
>>main() calls all the devsw init routines:
>>
>>    /*
>>     * March through the device switch probing for things.
>>     */
>>    for (i = 0; devsw[i] != NULL; i++)
>>	if (devsw[i]->dv_init != NULL)
>>	    (devsw[i]->dv_init)();
>>    printf("BIOS %dkB/%dkB available memory\n", bios_basemem / 1024,
>>bios_extmem / 1024);
>>
>>-- 
>>John Baldwin
>