improve logging for fakeudev, improve comments

src/ugrd/fs/fakeudev.py

@@ -10,18 +10,30 @@
 
 
 def fake_dm_udev(self) -> str:
-    """returns a shell function to fake udev for dm devices."""
+    """returns a shell function to fake udev for dm devices.
+    Previously, ${dm}/uevent was sourced, but this has the potential to crash the shell
+
+    Checks for the existence of /sys/block/dm-* entries,
+    for each entry, it checks if the device has a 'dev' and name file, it not, skips it.
+    Fully initailzed deviecs should have a 'dm/name' file.
+
+    Reads the 'dev' file to get the device's major and minor numbers,
+    uses these to create a udev database file in /run/udev/data/b<MAJOR>:<MINOR>.
+    writes 'E:DM_UDEV_PRIMARY_SOURCE_FLAG=1\n' to this file, which signals to systemd that udev is functioning for this device.
+    """
     return r"""
     for dm in /sys/block/dm-*; do
         if [ ! -e "${dm}/dev" ]; then
+            ewarn "Skipping fakeudev for device without 'dev' file: ${dm}"
             continue
         fi
         if [ ! -e "${dm}/dm/name" ]; then
+            ewarn "Skipping fakeudev for device without 'dm/name' file: ${dm}"
             continue
         fi
         dev_name=$(cat ${dm}/dm/name)
         majmin=$(cat "${dm}/dev")
-        einfo "Faking udev for: ${dev_name}"
+        einfo "[${majmin}] Faking udev for: ${dev_name}"
         udev_db_file="/run/udev/data/b${majmin}"
         printf 'E:DM_UDEV_PRIMARY_SOURCE_FLAG=1\n' > "${udev_db_file}"
     done