[OE-core] [wic][PATCH 1/6] wic: use truncate utility to create sparse file

[Ed Bartosh]

Used truncate instead of dd to create wic image for the
following reasons:
 - truncate syntax is much more clear
 - dd requires additional calculations of the image size
   in blocks
 - the way dd was used in the code is not entirely correct.
   It was still writing one block to the file, which made it not
   100% sparse.

Signed-off-by: Ed Bartosh <ed.bartosh at linux.intel.com>
---
 scripts/lib/wic/utils/fs_related.py | 12 +++---------
 1 file changed, 3 insertions(+), 9 deletions(-)

diff --git a/scripts/lib/wic/utils/fs_related.py b/scripts/lib/wic/utils/fs_related.py
index 2e74461..2658dcf 100644
--- a/scripts/lib/wic/utils/fs_related.py
+++ b/scripts/lib/wic/utils/fs_related.py
@@ -71,14 +71,8 @@ class DiskImage(Disk):
     def create(self):
         if self.device is not None:
             return
-
-        blocks = self.size / 1024
-        if self.size - blocks * 1024:
-            blocks += 1
-
-        # create disk image
-        dd_cmd = "dd if=/dev/zero of=%s bs=1024 seek=%d count=1" % \
-            (self.image_file, blocks)
-        exec_cmd(dd_cmd)
+        # create sparse disk image
+        cmd = "truncate %s -s %s" % (self.image_file, self.size)
+        exec_cmd(cmd)
 
         self.device = self.image_file
-- 
2.1.4