Avoid executing memdiskfind under Secure Boot

memdiskfind displays an ugly error message when running under Secure
Boot where access to /dev/mem is restricted:

| cannt open /dev/mem: Operation not permitted

If we can read from /dev/mem then skip the memdiskfind and instead
display a warning message.

diff --git a/components/9990-main.sh b/components/9990-main.sh
index b0e2a7b..7fb7ed3 100755 (executable)
--- a/components/9990-main.sh
+++ b/components/9990-main.sh
@@ -52,25 +52,31 @@ Live ()
                else
                        if [ -x /usr/bin/memdiskfind ]
                        then
-                               if MEMDISK=$(/usr/bin/memdiskfind)
+                               if ! dd if=/dev/mem of=/dev/zero bs=1 count=1 >/dev/null 2>&1
                                then
-                                       # We found a memdisk, set up phram
-                                       # Sometimes "modprobe phram" can not successfully create /dev/mtd0.
-                                       # Have to try several times.
-                                       max_try=20
-                                       while [ ! -c /dev/mtd0 ] && [ "$max_try" -gt 0 ]; do
-                                         modprobe phram "phram=memdisk,${MEMDISK}"
-                                         sleep 0.2
-                                         if [ -c /dev/mtd0 ]; then
-                                               break
-                                         else
-                                               rmmod phram
-                                         fi
-                                         max_try=$((max_try - 1))
-                                       done
-
-                                       # Load mtdblock, the memdisk will be /dev/mtdblock0
-                                       modprobe mtdblock
+                                       log_begin_msg "access to /dev/mem is restriced, skipping memdiskfind"
+                                       log_end_msg
+                               else
+                                       if MEMDISK=$(/usr/bin/memdiskfind)
+                                       then
+                                               # We found a memdisk, set up phram
+                                               # Sometimes "modprobe phram" can not successfully create /dev/mtd0.
+                                               # Have to try several times.
+                                               max_try=20
+                                               while [ ! -c /dev/mtd0 ] && [ "$max_try" -gt 0 ]; do
+                                                 modprobe phram "phram=memdisk,${MEMDISK}"
+                                                 sleep 0.2
+                                                 if [ -c /dev/mtd0 ]; then
+                                                       break
+                                                 else
+                                                       rmmod phram
+                                                 fi
+                                                 max_try=$((max_try - 1))
+                                               done
+
+                                               # Load mtdblock, the memdisk will be /dev/mtdblock0
+                                               modprobe mtdblock
+                                       fi
                                fi
                        fi