Description of problem:

grub2 network disfunctional under iPXE oprom(in OVMF guest)

This could be other components' bug, anything that involved in booting a Linux kernel over tftp server for a OVMF(UEFI) guest with iPXE oprom, which I am not that 100% sure which one is the root cause, filing this bz against grub2 as:
1) the current failing message was from grub2
2) iPXE could gain IP addr, and transfer data(shim.efi or grubx64.efi, depends on dhcpd.conf) from tftp.
3) made a standalone grub2 could workaround this issue(vmlinuz/initrd.img in grubx64.efi, that avoids using grub2 network stack)


if I am filling wrong component, pls help to change :-)
Version-Release number of selected component (if applicable):
on the DHCP/TFTP server side:
grub2-efi-2.02-0.16.el7.x86_64 (downgraded to grub2-efi-2.02-0.2.10.el7.x86_64 not helpful)
grub2-efi-modules (version same as grub2-efi)
shim-0.7-8.el7_0.x86_64 (downgraded to shim-0.7-5.2.el7.x86_64 not helpful)
tftp-server-5.2-11.el7.x86_64
dhcp-common-4.2.5-27.el7.x86_64
dhcp-libs-4.2.5-27.el7.x86_64
dhcp-4.2.5-27.el7.x86_64

DHCP/TFTP client side:
ipxe-roms-qemu-20130517-6.gitc4bce43.el7.noarch (installed on host)

Physical host:
qemu-kvm-rhev-2.1.2-20.el7.x86_64
bridge-utils-1.5-9.el7.x86_64
kernel-3.10.0-221.el7.x86_64


I dont think Linux kernel involved here, but they are from iso as below
RHEL-7.0-20140507.0-Server-x86_64-dvd1.iso
RHEL-6.6-20140926.0-Server-x86_64-dvd1.iso

How reproducible:
100%

Steps to Reproduce:
1. setup a isolated Linux bridge(w/o physical NIC attached), and define two VMs in libvirt, one as pxe/dhcp/tftp server and another one as the pxe client configured nic as first booting priority
-----------ovmf def
  <os>
    <type arch='x86_64' machine='pc-i440fx-rhel7.1.0'>hvm</type>
    <loader readonly='yes' type='pflash'>/usr/share/OVMF/OVMF_CODE.fd</loader>
    <nvram template='/usr/share/OVMF/OVMF_VARS.fd'>/var/lib/libvirt/qemu/nvram/uefi-rhel6_VARS.fd</nvram>
    <bootmenu enable='yes'/>
  </os>
-----------
=========== nic as first booting priority
    <interface type='bridge'>
      <mac address='52:54:00:96:79:19'/>
      <source bridge='uefi-pxe'/>
      <target dev='vnet1'/>
      <model type='virtio'/>
      <boot order='1'/>
      <alias name='net0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
    </interface>
=============

Illustrated as:

pxe server vm(vnet0) <-> Linux bridge(named uefi-pxe) <-> (vnet1)pxe client VM(using OVMF, and iPXE oprom)

                                                        |
                                                      tcpdump here


inside the pxe server vm:
cat /etc/dhcp/dhcpd.conf 
option space PXE;
option PXE.mtftp-ip    code 1 = ip-address;
option PXE.mtftp-cport code 2 = unsigned integer 16;
option PXE.mtftp-sport code 3 = unsigned integer 16;
option PXE.mtftp-tmout code 4 = unsigned integer 8;
option PXE.mtftp-delay code 5 = unsigned integer 8;

subnet 192.168.0.0 netmask 255.255.255.0 {
  range 192.168.0.2 192.168.0.250;

  class "pxeclients" {
    match if substring (option vendor-class-identifier, 0, 9) = "PXEClient";
    next-server 192.168.0.1;
    if option arch = 00:07 {
      filename "shim.efi";
#      filename "non-secboot/non-secbootx64-with-rhel66ga-vmlinuz-initrd-with-updated-grub.cfg.efi";
# boot to standalone all-in-one(vmlinuz initrd grub.cfg inside) works
#      filename "grubx64.efi";
# boot to grubx64.efi directly wont help
      } else if option arch = 00:09 {
      filename "shim.efi";
      }
    }
  }


# grep -i disable /etc/xinetd.d/tftp 
	disable			= no

# pwd
/var/lib/tftpboot
# ls 
grubx64.efi  shim.efi grub.cfg
set timeout=5

menuentry 'Red Hat Enterprise Linux Server release 7.0 GA' --class os {
     insmod net 
     insmod efinet
     insmod tftp
     insmod gzio
     insmod part_gpt
     insmod efi_gop
     insmod efi_uga
     #set net_default_server=192.168.0.1
     #net_bootp
     # in case DHCP wont work for grub2
     #net_add_addr eno0 efinet0 192.168.0.9
     #### indeed, both net_bootp and net_add_addr wont help under iPXE oprom
     echo 'Network status: '
     net_ls_cards
     net_ls_addr
     net_ls_routes

     echo 'Loading Red Hat Enterprise Linux Server release 7.0 GA kernel ...'
     linuxefi (tftp)/rhel70ga/vmlinuz ip=dhcp \
     inst.repo=nfs:192.168.0.1:/home/installation_source/RHEL7.0GA/RHEL-7.0-20140507.0-Server-x86_64-dvd1.iso \
     console=ttyS0,115200 console=tty

     echo 'Loading Red Hat Enterprise Linux Server release 7.0 GA initial ramdisk ...'
     initrdefi (tftp)/rhel70ga/initrd.img
}


2. check services are up 
systemctl status dhcpd.service tftp.service etc

3. virsh start pxe-client-vm
and immediately start tcpdump
tcpdump -vvvvn -i vnet1 > tcpdump.txt

virsh qemu-monitor-command pxe-client-vm --hmp --cmd "info qtree" | grep -i romfile
        romfile = ""
        romfile = "vgabios-cirrus.bin"
        romfile = "pxe-virtio.rom"              -> make sure VM is using iPXE oprom


and the booting procedure is like:

1 OVMF -> 2 (builtin DXE) or (iPXE oprom) -> 3 DHCP,TFTP(request shim.efi then grubx64.efi) -> 4 accord to grub.cfg might request vmlinuz and initrd.img

Actual results:

after 3 DHCP,TFTP downloading the filename configured on dhcpd.conf, grubx64.efi or shim.efi stops sending requests to tftp server for grub.cfg vmlinuz, and raise error that file not exist(and they actually lays on tftp server)

Expected results:
shim.efi should request for grubx64.efi and later files (when filename sets to shim)
or
grubx64.efi should bring network and request for grub.cfg and vmlinuz initrd.img etc


Additional info:

*IF* change the ovmf guest to use builtin virtio-net driver instead of iPXE oprom, then it will work, though net_bootp still raise error, tcpdump shows shim.efi requests for grubx64.efi then grub.cfg then vmlinuz.

<rom file=''/> append this to the libvirt vm def. for builtin driver.




vm screen dumps and tcpdumps would be attached later.