feat(lvm): use generated filter when none is set

Previously, the lvm device filter generated by dracut
would not be used if any lvm.conf file existed in the
initrd.  Change this so that the generated filter will
be used when the included lvm.conf has no filter set.

modules.d/90lvm/lvm_scan.sh

@@ -10,6 +10,7 @@ LVS=$(getargs rd.lvm.lv -d rd_LVM_LV=)
 
 # shellcheck disable=SC2174
 [ -d /etc/lvm ] || mkdir -m 0755 -p /etc/lvm
+[ -d /run/lvm ] || mkdir -m 0755 -p /run/lvm
 # build a list of devices to scan
 lvmdevs=$(
     for f in /tmp/.lvm_scan-*; do
@@ -18,22 +19,6 @@ lvmdevs=$(
     done
 )
 
-if [ ! -e /etc/lvm/lvm.conf ]; then
-    {
-        echo 'devices {'
-        printf '    filter = [ '
-        for dev in $lvmdevs; do
-            printf '"a|^/dev/%s$|", ' "$dev"
-        done
-        echo '"r/.*/" ]'
-        echo '}'
-
-        echo 'global {'
-        echo '}'
-    } > /etc/lvm/lvm.conf
-    lvmwritten=1
-fi
-
 check_lvm_ver() {
     maj=$1
     min=$2
@@ -47,6 +32,75 @@ check_lvm_ver() {
     return 1
 }
 
+no_lvm_conf_filter() {
+    if [ ! -e /etc/lvm/lvm.conf ]; then
+        return 0
+    fi
+
+    if [ -e /run/lvm/initrd_no_filter ]; then
+        return 0
+    fi
+
+    if [ -e /run/lvm/initrd_filter ]; then
+        return 1
+    fi
+
+    if [ -e /run/lvm/initrd_global_filter ]; then
+        return 1
+    fi
+
+    # Save lvm config results in /run to avoid running
+    # lvm config commands for every PV that's scanned.
+
+    filter=$(lvm config devices/filter | grep "$filter=")
+    if [ -n "$filter" ]; then
+        printf '%s\n' "$filter" > /run/lvm/initrd_filter
+        return 1
+    fi
+
+    global_filter=$(lvm config devices/global_filter | grep "$global_filter=")
+    if [ -n "$global_filter" ]; then
+        printf '%s\n' "$global_filter" > /run/lvm/initrd_global_filter
+        return 1
+    fi
+
+    # /etc/lvm/lvm.conf exists with no filter setting
+    true > /run/lvm/initrd_no_filter
+    return 0
+}
+
+# If no lvm.conf exists, create a basic one with a global section.
+if [ ! -e /etc/lvm/lvm.conf ]; then
+    {
+        echo 'global {'
+        echo '}'
+    } > /etc/lvm/lvm.conf
+    lvmwritten=1
+fi
+
+# Save the original lvm.conf before appending a filter setting.
+if [ ! -e /etc/lvm/lvm.conf.orig ]; then
+    cp /etc/lvm/lvm.conf /etc/lvm/lvm.conf.orig
+fi
+
+# If the original lvm.conf does not contain a filter setting,
+# then generate a filter and append it to the original lvm.conf.
+# The filter is generated from the list PVs that have been seen
+# so far (each has been processed by the lvm udev rule.)
+if no_lvm_conf_filter; then
+    {
+        echo 'devices {'
+        printf '    filter = [ '
+        for dev in $lvmdevs; do
+            printf '"a|^/dev/%s$|", ' "$dev"
+        done
+        echo '"r/.*/" ]'
+        echo '}'
+    } > /etc/lvm/lvm.conf.filter
+    lvmfilter=1
+    cat /etc/lvm/lvm.conf.orig /etc/lvm/lvm.conf.filter > /etc/lvm/lvm.conf
+fi
+
 # hopefully this output format will never change, e.g.:
 #   LVM version:     2.02.53(1) (2009-09-25)
 OLDIFS=$IFS
@@ -99,8 +153,13 @@ fi
 
 if [ "$lvmwritten" ]; then
     rm -f -- /etc/lvm/lvm.conf
+elif [ "$lvmfilter" ]; then
+    # revert filter that was appended to existing lvm.conf
+    cp /etc/lvm/lvm.conf.orig /etc/lvm/lvm.conf
+    rm -f -- /etc/lvm/lvm.conf.filter
 fi
 unset lvmwritten
+unset lvmfilter
 
 udevadm settle