live: drop IniciarSesion script when uefi booting into linux

Replace IniciarSesion script in favor of native Python code when booting
a UEFI system into Linux. This completes the implementation of booting
into an OS on a UEFI compliant system.

src/utils/boot.py

@@ -43,6 +43,30 @@ def _boot_uefi_windows(disk, part, mountpoint):
     finally:
         umount(esp_mountpoint)
 
+def _boot_uefi_linux(disk, part, mountpoint):
+    logging.info(f'Booting Linux system')
+    bootlabel = f'Part-{disk:02d}-{part:02d}'
+    esp, esp_disk, esp_part_number = get_efi_partition(disk)
+    esp_mountpoint = esp.replace('dev', 'mnt')
+    if not mount_mkdir(esp, esp_mountpoint):
+        raise RuntimeError(f'Unable to mount detected EFI System Partition at {esp} into {esp_mountpoint}')
+
+    loader_paths = [f'{esp_mountpoint}/EFI/{bootlabel}/Boot/shimx64.efi',
+                    f'{esp_mountpoint}/EFI/ubuntu/shimx64.efi']
+    try:
+        for efi_app in loader_paths:
+            if os.path.exists(efi_app):
+                loader = efi_app[len(esp_mountpoint):]
+                logging.info(f'Found bootloader at ESP partition: {loader}')
+                break
+        else:
+            raise RuntimeError(f'Unable to locate Linux EFI bootloader shimx64.efi')
+
+        efibootmgr_delete_bootentry(bootlabel)
+        efibootmgr_create_bootentry(esp_disk, esp_part_number, loader, bootlabel)
+        efibootmgr_bootnext(bootlabel)
+    finally:
+        umount(esp_mountpoint)
 
 def boot_os_at(disk, part):
     if not is_uefi_supported():
@@ -55,9 +79,12 @@ def boot_os_at(disk, part):
 
     logging.info(f'Booting system at {device}. Probing OS family...')
     os_family = get_os_family(mountpoint)
-    if os_family == OSFamily.WINDOWS:
-        _boot_uefi_windows(disk, part, mountpoint)
-    elif os_family == OSFamily.LINUX:
-        raise NotImplementedError('WIP: Linux UEFI boot not implemented yet.')
-    else:
-        raise RuntimeError('Unknown OS family')
+    try:
+        if os_family == OSFamily.WINDOWS:
+            _boot_uefi_windows(disk, part, mountpoint)
+        elif os_family == OSFamily.LINUX:
+            _boot_uefi_linux(disk, part, mountpoint)
+        else:
+            raise RuntimeError('Unknown OS family')
+    finally:
+        umount(mountpoint)