fix(check_live_ram): increase /run tmpfs size, if needed

Check the size and available space in /run to enlarge it,
  if needed.
Introduce the check_meminfo() function to replace a less
  versatile sed call.
Also, use local variables.

modules.d/99base/dracut-lib.sh

@@ -1130,6 +1130,18 @@ show_memstats() {
     esac
 }
 
+# parameter: memory_name: example:  MemTotal:
+# Check /proc/meminfo
+# echo the field value, if present.
+check_meminfo() {
+    local - m sz u
+    set +x
+    while read -r m sz u || [ "$m" ]; do
+        [ "$m" = "$1" ] && echo "$sz" && return 0
+    done < /proc/meminfo
+    return 1
+}
+
 remove_hostonly_files() {
     rm -fr /etc/cmdline /etc/cmdline.d/*.conf "$hookdir/initqueue/finished"
     if [ -f /lib/dracut/hostonly-files ]; then
@@ -1152,13 +1164,20 @@ load_fstype() {
     modprobe "$1"
 }
 
-# parameter: size of live image
+# parameter: size of live image in MiB
 # calls emergency shell if ram size is too small for the image
+# Increase /run tmpfs size, if needed.
 check_live_ram() {
+    local minmem imgsize memsize runsize runavail
     minmem=$(getarg rd.minmem)
     minmem=${minmem:-1024}
     imgsize=$1
-    memsize=$(($(sed -n 's/MemTotal: *\([[:digit:]]*\).*/\1/p' /proc/meminfo) / 1024))
+    memsize=$(($(check_meminfo MemTotal:) >> 10))
+    # shellcheck disable=SC2046
+    set -- $(findmnt -bnro SIZE,AVAIL /run)
+    # bytes to MiB
+    runsize=$(($1 >> 20))
+    runavail=$(($2 >> 20))
 
     if [ -z "$imgsize" ]; then
         warn "Image size could not be determined"
@@ -1174,5 +1193,8 @@ check_live_ram() {
          echo \n/" /usr/bin/dracut-emergency
 
         emergency_shell
+    elif [ $((runavail - imgsize)) -lt "$minmem" ]; then
+        # Increase /run tmpfs size, if needed.
+        mount -o remount,size=$((runsize - runavail + imgsize + minmem))M /run
     fi
 }