Description of problem:

We have a customer deploying systems using Upstream Satellite product.
All his systems are on UEFI and boot through the network, loading Grub2 and a configuration file used to chainload to the local disk of the system, similar to this excerpt below:
-------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------
menuentry 'Chainload Grub2 EFI from ESP' --id local {
  unset root
  # search for local disk EFI partition
  search --file --no-floppy --set=root /EFI/BOOT/BOOTX64.EFI
  echo found $root
  # select the right local disk bootloader
  if [ -f ($root)/EFI/BOOT/grubx64.efi ]; then
    chainloader ($root)/EFI/BOOT/grubx64.efi
  elif [ -f ($root)/EFI/fedora/grubx64.efi ]; then
    chainloader ($root)/EFI/fedora/grubx64.efi
  ...
-------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------

When the system has its EFI partition in Software Raid, the "search --file" command returns "md/boot_efi" device as new root device, which prevents "chainloader" command from working because the device is not a EFI disk but a virtual device, which is not supported by the "chainloader" command.

The solution consists in adding a new "--efidisk-only" option to "search" to limit searching for EFI disks only:
-------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------
search --file --no-floppy --efidisk-only --set=root /EFI/BOOT/BOOTX64.EFI
-------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------


Version-Release number of selected component (if applicable):

all grub releases


How reproducible:

Always

Steps to Reproduce:
1. Setup a VM with EFI and softraid
2. Boot the VM from the network using chainloading grub.cfg above

Actual results:

"not a valid root device" error

Expected results:

can chainload

Additional info:

A partial workaround consists in adding a "--hint-efi" on the various disks making the softraid, e.g. "--hint-efi=hd0, --hint-efi=hd1," but this doesn't always work because there is no way to avoid "search" from returning the softraid.