From 94cfe59ff90a8e874696a7574555f56986b781ac Mon Sep 17 00:00:00 2001
From: Eric Gumtow <egumtow@slac.stanford.edu>
Date: Tue, 17 Feb 2026 16:09:15 -0800
Subject: [PATCH 1/2] down network interfaces behind USB ports

---
 custom_files/disable_disconnected_nics.sh | 30 +++++++++++++++++++++--
 1 file changed, 28 insertions(+), 2 deletions(-)

diff --git a/custom_files/disable_disconnected_nics.sh b/custom_files/disable_disconnected_nics.sh
index 745df23..f9f3995 100755
--- a/custom_files/disable_disconnected_nics.sh
+++ b/custom_files/disable_disconnected_nics.sh
@@ -3,9 +3,35 @@
 # 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" =~ enp0s[0-9]{1,}f[0-9]u[0-9]{1,} ]] ; then
+            # Naming convention documentation: https://www.freedesktop.org/software/systemd/man/latest/systemd.net-naming-scheme.html
+            # Table 3: slot naming schemes
+            #  en            --> ethernet
+            #  p0            --> PCI domain 0
+            #  s[0-9]{1,}    --> PCI slot 0 or higher, seems to be decimal from code (safe_atou*())
+            #  f[0-9]        --> PCI function 0 to 9
+            #  u[0-9]{1,}    --> USB port 0 or higher
+            #
+            # 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

From 86bce7ec2fca1ee9f2b0f1dc1152599d406ddd88 Mon Sep 17 00:00:00 2001
From: Eric Gumtow <egumtow@slac.stanford.edu>
Date: Wed, 18 Feb 2026 09:55:24 -0800
Subject: [PATCH 2/2] use + one-or-more matching, and match PCI domains higher
 than 0

---
 custom_files/disable_disconnected_nics.sh | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/custom_files/disable_disconnected_nics.sh b/custom_files/disable_disconnected_nics.sh
index f9f3995..fece9af 100755
--- a/custom_files/disable_disconnected_nics.sh
+++ b/custom_files/disable_disconnected_nics.sh
@@ -11,14 +11,15 @@ should_down()
         fi
 
         # Check if the interface is bridged by USB (PCI -> USB -> ethernet)
-        if [[ "$1" =~ enp0s[0-9]{1,}f[0-9]u[0-9]{1,} ]] ; then
+        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
-            #  p0            --> PCI domain 0
-            #  s[0-9]{1,}    --> PCI slot 0 or higher, seems to be decimal from code (safe_atou*())
-            #  f[0-9]        --> PCI function 0 to 9
-            #  u[0-9]{1,}    --> USB port 0 or higher
+            #  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