Refactor finding EFI images

This will be useful for a follow up commit, which will attempt to look
for a binary relative to QEMU's prefix. It happens to simplify the code
as well.

Signed-off-by: Nathan Chancellor <nathan@kernel.org>

Author: nathanchance

boot-qemu.py

@@ -378,13 +378,11 @@ def get_efi_args(guest_arch):
             Path("edk2/aarch64/QEMU_EFI.fd"),  # Arch Linux (current)
             Path("edk2-armvirt/aarch64/QEMU_EFI.fd"),  # Arch Linux (old)
             Path("qemu-efi-aarch64/QEMU_EFI.fd"),  # Debian and Ubuntu
-            None  # Terminator
         ],
         "x86_64": [
             Path("edk2/x64/OVMF_CODE.fd"),  # Arch Linux (current), Fedora
             Path("edk2-ovmf/x64/OVMF_CODE.fd"),  # Arch Linux (old)
             Path("OVMF/OVMF_CODE.fd"),  # Debian and Ubuntu
-            None  # Terminator
         ]
     }  # yapf: disable
 
@@ -394,12 +392,8 @@ def get_efi_args(guest_arch):
         )
         return []
 
-    for efi_img_location in efi_img_locations[guest_arch]:
-        if efi_img_location is None:
-            raise Exception(f"edk2 could not be found for {guest_arch}!")
-        efi_img = Path("/usr/share", efi_img_location)
-        if efi_img.exists():
-            break
+    usr_share = Path('/usr/share')
+    efi_img = utils.find_first_file(usr_share, efi_img_locations[guest_arch])
 
     if guest_arch == "arm64":
         # Sizing the images to 64M is recommended by "Prepare the firmware" section at
@@ -422,15 +416,8 @@ def get_efi_args(guest_arch):
         efi_vars_locations = [
             Path("edk2/x64/OVMF_VARS.fd"),  # Arch Linux and Fedora
             Path("OVMF/OVMF_VARS.fd"),  # Debian and Ubuntu
-            None  # Terminator
         ]
-        for efi_vars_location in efi_vars_locations:
-            if efi_vars_location is None:
-                raise Exception("OVMF_VARS.fd could not be found!")
-            efi_vars = Path('/usr/share', efi_vars_location)
-            if efi_vars.exists():
-                break
-
+        efi_vars = utils.find_first_file(usr_share, efi_vars_locations)
         efi_vars_qemu = base_folder.joinpath("images", guest_arch,
                                              efi_vars.name)
         shutil.copyfile(efi_vars, efi_vars_qemu)

utils.py

@@ -30,6 +30,29 @@ def die(string):
     sys.exit(1)
 
 
+def find_first_file(relative_root, possible_files):
+    """
+    Attempts to find the first option available in the list of files relative
+    to a specified root folder.
+
+    Parameters:
+        relative_root (Path): A Path object containing the folder to search for
+                              files within.
+        possible_files (list): A list of Paths that may be within the relative
+                               root folder. They will be automatically appended
+                               to relative_root.
+    Returns:
+        The full path to the first file found in the list. If none could be
+        found, an Exception is raised.
+    """
+    for possible_file in possible_files:
+        if (full_path := relative_root.joinpath(possible_file)).exists():
+            return full_path
+    raise Exception(
+        f"No files from list ('{', '.join(possible_files)}') could be found within '{relative_root}'!"
+    )
+
+
 def get_full_kernel_path(kernel_location, image, arch=None):
     """
     Get the full path to a kernel image based on the architecture and image