Reduce kdump memory consumption by not letting NetworkManager manage unneeded network interfaces

By default, NetworkManger will manage all the network interfaces and
try to set interface IFF_UP to get carrier state. Regardless of whether
the network interface is connected to a cable or not, the NIC driver
will allocate memory resources for e.g. ring buffers when setting IFF_UP.
This could be a waste of memory. For example it's found i40e consumes ~15GB
on a power machine. On this machine, i40e manages four interfaces but only
one interface is valid. This patch use "managed=false" to tell
NetworkManager to not manage network interfaces that are not needed by
kdump by putting 10-kdump-netif_allowlist.conf in the initramfs.

Signed-off-by: Coiby Xu <coxu@redhat.com>
Reviewed-by: Thomas Haller <thaller@redhat.com>
Reviewed-by: Philipp Rudo <prudo@redhat.com>

dracut-module-setup.sh

@@ -364,6 +364,29 @@ kdump_install_nmconnections() {
     echo > "${initdir}/usr/libexec/nm-initrd-generator"
 }
 
+kdump_install_nm_netif_allowlist() {
+    local _netif _except_netif _netif_allowlist _netif_allowlist_nm_conf
+
+    for _netif in $1; do
+        _per_mac=$(kdump_get_perm_addr "$_netif")
+        if [[ "$_per_mac" != 'not set' ]]; then
+            _except_netif="mac:$_per_mac"
+        else
+            _except_netif="interface-name:$_netif"
+        fi
+        _netif_allowlist="${_netif_allowlist}except:${_except_netif};"
+    done
+
+    _netif_allowlist_nm_conf=$_DRACUT_KDUMP_NM_TMP_DIR/netif_allowlist_nm_conf
+    cat << EOF > "$_netif_allowlist_nm_conf"
+[device-others]
+match-device=${_netif_allowlist}
+managed=false
+EOF
+
+    inst "$_netif_allowlist_nm_conf" "/etc/NetworkManager/conf.d/10-kdump-netif_allowlist.conf"
+}
+
 kdump_setup_bridge() {
     local _netdev=$1
     local _dev
@@ -558,6 +581,7 @@ kdump_install_net() {
     if [[ -n "$_netifs" ]]; then
         kdump_install_nmconnections
         apply_nm_initrd_generator_timeouts
+        kdump_install_nm_netif_allowlist "$_netifs"
     fi
 }