Read from the store if the filename reported by losetup has been truncated (the

loop driver stores only the first 64 chars of the filename).  In this case, we
need to read through the store until we find the domain using the device, and
read the configured filename from there instead.

Signed-off-by: Ewan Mellor <ewan@xensource.com>

diff --git a/tools/examples/block b/tools/examples/block
index e84d1fb4158b278ac817e394619b6715b14587e5..b37f8fdbd43448bc36923009ea4c8633d6fbdb3d 100644 (file)
--- a/tools/examples/block
+++ b/tools/examples/block
@@ -250,7 +250,7 @@ case "$command" in
       file)
         # Canonicalise the file, for sharing check comparison, and the mode
         # for ease of use here.
-        file=$(readlink -f "$p")
+        file=$(readlink -f "$p") || fatal "$p does not exist."
         mode=$(canonicalise_mode "$mode")
 
         claim_lock "block"
@@ -271,8 +271,7 @@ mount it read-write in a guest domain."
             continue
           fi
 
-          f=$(losetup "$dev" 2>/dev/null) || f='()'
-          f=$(echo "$f" | sed -e 's/.*(\(.*\)).*/\1/g')
+          f=$(losetup "$dev" 2>/dev/null) || f=''
 
           if [ "$f" ]
           then
@@ -282,6 +281,38 @@ mount it read-write in a guest domain."
               continue
             fi
 
+            f=$(echo "$f" | sed -e 's/.*(\(.*\)).*/\1/g')
+
+            # $f is the filename, as read from losetup, but the loopback
+            # driver truncates filenames at 64 characters, so we need to go
+            # trawling through the store if it's longer than that.  Truncation
+            # is indicated by an asterisk at the end of the filename.
+            if expr index "$f" '*' >/dev/null
+            then
+              found=""
+              for dom in $(xenstore-list "$XENBUS_BASE_PATH")
+              do
+                for domdev in $(xenstore-list "$XENBUS_BASE_PATH/$dom")
+                do
+                  d=$(xenstore_read_default \
+                        "$XENBUS_BASE_PATH/$dom/$domdev/node" "")
+                  if [ "$d" == "$dev" ]
+                  then
+                    f=$(xenstore_read "$XENBUS_BASE_PATH/$dom/$domdev/params")
+                    found=1
+                    break 2
+                  fi
+                done
+              done
+
+              if [ ! "$found" ]
+              then
+                # This loopback device is in use by someone else, so skip it.
+                log debug "Loopback sharing check skips device $dev."
+                continue
+              fi
+            fi
+
             f=$(readlink -f "$f")
 
             if [ "$f" == "$file" ]