cache: add code to cache the oglive boot files

Add update_live_cache() implementing the legacy script
updateBootCache()

Copy the ogvmlinuz and oginitrd.img files into cache after
a partition and format command with an available cache partition.

src/live/ogOperations.py

@@ -541,6 +541,7 @@ class OgLiveOperations:
             fs = part["filesystem"].lower()
             if fs == 'cache':
                 mount_cache()
+                update_live_cache()
 
         logging.info('Partition setup command OK')
         result = self.refresh(ogRest)

src/utils/cache.py

@@ -7,6 +7,7 @@
 # (at your option) any later version.
 
 import logging
+import shutil
 import os
 
 from src.utils.fs import mount_mkdir, umount
@@ -66,3 +67,50 @@ def generate_cache_txt():
             return
         content = ','.join(files)
         write_cache_txt(content)
+
+def _read_checksum(file_path):
+    res = ''
+    try:
+        with open(file_path, 'r') as f:
+            res = f.read()
+    except (FileNotFoundError, PermissionError, OSError) as e:
+        logging.info(f'Cannot read checksum file {file_path}: {e}')
+    return res
+
+def update_live_cache():
+    live_dir = os.getenv('oglivedir')
+
+    if not live_dir:
+        logging.warning('No oglivedir environment variable defined')
+        return
+
+    cache_mnt = mount_cache()
+    if not cache_mnt:
+        logging.info(f'No cache partition available, skipping live cache generation')
+        return
+
+    src_dir = f"/opt/oglive/tftpboot/{live_dir}"
+    dst_dir = f"{cache_mnt}/boot/{live_dir}"
+
+    if not os.path.exists(src_dir):
+        logging.info(f'{src_dir} not found')
+        return
+
+    os.makedirs(dst_dir, exist_ok=True)
+
+    sum_extension = '.sum'
+
+    files = ['ogvmlinuz', 'oginitrd.img']
+
+    for file_name in files:
+        server_file = f'{src_dir}/{file_name}'
+        client_file = f'{dst_dir}/{file_name}'
+        server_checksum = _read_checksum(server_file + sum_extension)
+        client_checksum = _read_checksum(client_file + sum_extension)
+
+        if server_checksum and server_checksum != client_checksum:
+            logging.info(f'Updating live cache {client_file}')
+            shutil.copyfile(server_file, client_file)
+            shutil.copyfile(server_file + sum_extension, client_file + sum_extension)
+        else:
+            logging.info(f'{client_file} is already up to date')