Make function get_disk_size () be more tolerant when querying /sys fo…

…r number of disk blocks.

See issue #1370 for more details.

usr/share/rear/conf/default.conf

@@ -474,6 +474,16 @@ PXE_CONFIG_GRUB_STYLE=
 # Default is empty which means prompting what to do next and after a timeout boot next option defined by BIOS
 PXE_RECOVER_MODE=
 
+# Certain operation might need longer time to kick in and more retries might be desirable.
+# REAR_SLEEP_DELAY (in sec.) is general delay for operation.
+REAR_SLEEP_DELAY=1
+# REAR_MAX_RETRIES is maximum number of attempts that should be executed before operation is aborted.
+# Maximum timeout for operation calculates as REAR_SLEEP_DELAY * REAR_MAX_RETRIES
+# This retries / timeout operation is currently implemented only in get_disk_size (),
+# so if you have trouble with error messages like:
+# 'Could not determine size of disk <device> ...' tweaking of REAR_SLEEP_DELAY and REAR_MAX_RETRIES might help.
+REAR_MAX_RETRIES=5
+
 ##
 # internal BACKUP stuff
 ##

usr/share/rear/lib/layout-functions.sh

@@ -530,10 +530,7 @@ get_disk_size() {
 
     local block_size=$(get_block_size ${disk_name%/*})
 
-    [ -r /sys/block/$disk_name/size ]
-    BugIfError "Could not determine size of disk $disk_name, please file a bug."
-
-    local nr_blocks=$( < /sys/block/$disk_name/size)
+    local nr_blocks=$(retry_command "cat /sys/block/$disk_name/size")
     local disk_size=$(( nr_blocks * block_size ))
 
     ### Make sure we always return a number
@@ -590,3 +587,27 @@ is_disk_a_pv() {
 function is_multipath_path {
     [ "$1" ] && type multipath &>/dev/null && multipath -c /dev/$1 &>/dev/null
 }
+
+# retry_command () is binded with REAR_SLEEP_DELAY and REAR_MAX_RETRIES.
+# This function will do maximum of REAR_MAX_RETRIES command execution
+# and will sleep REAR_SLEEP_DELAY after each unsuccessful command execution.
+# Function returns command result as soon as it succeeded.
+function retry_command () {
+    command="$1"
+
+    for pass in trial verification ; do
+        until result=$($command); do
+            sleep $REAR_SLEEP_DELAY
+
+            retry=$((retry+1))
+
+            if [[ $retry -eq $REAR_MAX_RETRIES ]]; then
+                # No success until now, we should end function and throw error.
+                Error  "Could not successfully finish command: '$command'"
+                break 2;
+            fi
+        done
+    done
+
+    echo $result
+}