svn commit: r314948 - in head: lib/libstand sys/boot/i386/libi386

[Baptiste Daroussin]

On Fri, May 26, 2017 at 12:27:45PM +0300, Andriy Gapon wrote:
> On 09/03/2017 08:01, Mariusz Zaborski wrote:
> > Author: oshogbo
> > Date: Thu Mar  9 06:01:24 2017
> > New Revision: 314948
> > URL: https://svnweb.freebsd.org/changeset/base/314948
> > 
> > Log:
> >   Try to extract the RFC1048 data from PXE. If we get enough info we can skip
> >   the bootp(). It removes unnecessary DHCP request from pxeloader.
> >   
> >   Submitted by:	kczekirda
> >   Sponsored by:	Oktawave
> >   Initiated by:	Matthew Dillon
> >   Reviewed by:	smh, gnn, bapt, oshogbo
> >   MFC after:	3 weeks
> >   Differential Revision:	https://reviews.freebsd.org/D9847
> 
> Sorry for being late to the party, but this being head hopefully not too late.
> 
> I am not sure that I agree with the spirit of this change.

I just figured out it also breaks chainloading with ipxe (like qemu does) and it
does not request the rootpath if not passed to the ipxe first.

I'm now really thinking the our loader deserves its own DHCP value.

We should also give it some tags so people can provide it the information they
want depending on the tags (like hey this is the fbsd loader give it that
rootpath).

> 
> There are network boot setups that do depend on the "unnecessary" DHCP request
> from pxeboot.  For example, a DHCP server could be configured to return a
> different set of parameters depending on a particular PXE client.  I personally
> use a configuration where the DCHP server sends a boot menu[*] to a PXE client
> that's built into network cards.  If a FreeBSD boot is selected and pxeboot is
> started, then the server sends parameters required for the FreeBSD boot
> (root-path, etc) in response to the request from pxeboot.
> I don't see how I can keep that working after this change.
> 
> Additionally, as far as I can tell, we only get cached
> PXENV_PACKET_TYPE_BINL_REPLY.  This might cause a problem in environments where
> a separate PXE server (Proxy DHCP) is used.  In that case the reply might not
> have the network configuration information which would actually be in
> PXENV_PACKET_TYPE_DHCP_ACK.
> An example of such a setup is described here:
> https://n0dy.com/blog/2014/09/14/network-booting-with-dnsmasq-in-proxy-mode/
> Using a separate PXE server is not uncommon in corporate environments too.
> 
> In general, I think that the change was not thought through to cover scenarios
> beyond the basic unattended, FreeBSD-only, single DHCP server network boots.
> That scenario is, of course, very common, but it is not the only one.
> 
> At minimum, I would like to have a compile time option to control whether
> pxeboot should send a DHCP request of its own or rely entirely on the cached
> information.  Or maybe pxeboot could be smart enough to do the former if the
> cached reply is missing some required information like the root-path.
> Right now, there is no bootp(BOOTP_PXE) under any conditions.
> 
> And my apologies again for missing the original discussion.
> My focus was somewhere else at the time.
> 
> [*] It uses PXE_BOOT_MENU and PXE_MENU_PROMPT vendor options for that.
> 
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