[Bug 1813541] Re: Shim uses wrong TFTP server IP in proxyDHCP mode

[Alkis Georgopoulos]

Pseudocode for UEFI/BIOS firmwares:
If the DHCP server doesn't offer a boot filename,
and a proxyDHCP server is available,
then use the boot filename from the proxyDHCP offer,
and set TFTP=proxyDHCP.

Pseudocode for shim:
If UEFI reports that it used proxyDHCP, then use that one for the TFTP server.
No decision to be done here; the decision was already done by UEFI in the previous step.
Also, note that there's no "boot filename" involved; that too, was done by UEFI in the previous step.
It's just about deciding where the TFTP server is.

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https://bugs.launchpad.net/bugs/1813541

Title:
  Shim uses wrong TFTP server IP in proxyDHCP mode

Status in shim package in Ubuntu:
  New

Bug description:
  This works fine:
  UEFI > real DHCP > shimx64.efi over TFTP > grubx64.efi over TFTP.

  In the scenario above, if we change "real" with "proxy", it fails,
  because it's trying to download grubx64.efi from the real DHCP server
  instead of the proxy one.

  A proxy DHCP server is one that only sends the boot filename, and
  leaves the IP assignments to the real DHCP server. We use that a lot
  in the ltsp.org and in other netbooting projects, as it avoids the
  need for a special network setup.

  Sample dnsmasq.conf for proxy setup:

  enable-tftp
  tftp-root=/var/lib/tftpboot
  dhcp-range=10.161.254.0,proxy,255.255.255.0
  pxe-service=X86-64_EFI,"Boot from network",shimx64.efi

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