down network interfaces behind USB ports

custom_files/disable_disconnected_nics.sh

@@ -3,9 +3,36 @@
 # Get a list of all network interfaces (excluding loopback)
 interfaces=$(ls /sys/class/net | grep -v lo)
 
+should_down()
+{
+        # Check if the interface is disconnected (carrier not detected)
+        if [[ -f "/sys/class/net/$1/carrier" && "$(cat /sys/class/net/$1/carrier)" == "0" ]]; then
+            return 1
+        fi
+
+        # Check if the interface is bridged by USB (PCI -> USB -> ethernet)
+        if [[ "$1" =~ enp[0-9]+s[0-9]+f[0-9]u[0-9]+ ]] ; then
+            # Naming convention documentation: https://www.freedesktop.org/software/systemd/man/latest/systemd.net-naming-scheme.html
+            # Table 3: slot naming schemes
+            #  en         --> ethernet
+            #  p[0-9]+    --> PCI domain 0 or higher
+            #  s[0-9]+    --> PCI slot 0 or higher
+            #  f[0-9]     --> PCI function 0 to 9
+            #  u[0-9]+    --> USB port 0 or higher
+            # all numbers seem to be in decimal from examining the code (safe_atou*()).
+            #
+            # Minh has "enp0s20f0u7u4", which matches and additionally is behind a second USB port (u7u4).
+            return 1
+        fi
+
+        return 0
+}
+
 for iface in $interfaces; do
-        # Check if the interface is disconnected (carrier detected)
-        if [[ -f "/sys/class/net/$iface/carrier" ]] && [[ "$(cat /sys/class/net/$iface/carrier)" == "0" ]]; then
+        if [[ $(should_down $iface) == "1" ]]; then
+            echo "downing iface $iface"
             ip link set dev $iface down
+        else
+            echo "up iface $iface"
         fi
 done