xen/block-losetup-retry.diff

Index: xen-unstable/tools/examples/block
===================================================================
--- xen-unstable.orig/tools/examples/block
+++ xen-unstable/tools/examples/block
@@ -274,9 +274,12 @@ case "$command" in
 mount it read-write in a guest domain."
         fi
 
-        loopdev=''
-        for dev in /dev/loop*
+        losetup_failure=1
+        for do_losetup in 1 2 3
         do
+         loopdev=''
+         for dev in /dev/loop*
+         do
           if [ ! -b "$dev" ]
           then
             continue
@@ -360,14 +363,20 @@ mount it read-write in a guest domain."
               loopdev="$dev"
             fi
           fi
-        done
+         done
+
+         if [ "$loopdev" = '' ]
+         then
+           fatal 'Failed to find an unused loop device'
+         fi
 
-        if [ "$loopdev" = '' ]
+         losetup "$loopdev" "$file" && losetup_failure="" && break
+        done
+        if [ "$losetup_failure" ]
         then
-          fatal 'Failed to find an unused loop device'
+          fatal 'losetup $loopdev $file'
         fi
 
-        do_or_die losetup "$loopdev" "$file"
         xenstore_write "$XENBUS_PATH/node" "$loopdev"
         write_dev "$loopdev"
         release_lock "block"
@@ -390,8 +399,18 @@ mount it read-write in a guest domain."
 
       file)
         node=$(xenstore_read "$XENBUS_PATH/node")
-	losetup -d "$node"
-	exit 0
+
+        #In case the loopback is temporarily blocked, retry the losetup -d.
+        for i in 1 2 3 4 5
+        do
+          if losetup -d "$node"
+          then
+            exit 0
+          fi
+          sleep 1
+        done
+        log err "losetup -d $node failed."
+        exit 1
 	;;
 
       "")