wic: use truncate utility to create sparse files

Used truncate instead of dd to create wic images for the
following reasons:
 - dd doesn't preserve sparseness
 - 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 always correct.
   In some cases it was writing one block to the file which makes
   it not 100% sparse.

[YOCTO #9099]

Signed-off-by: Ed Bartosh <ed.bartosh@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

2 files changed, 8 insertions, 24 deletions

diff --git a/scripts/lib/wic/partition.py b/scripts/lib/wic/partition.py
index 227b685137..6d21193902 100644
--- a/scripts/lib/wic/partition.py
+++ b/scripts/lib/wic/partition.py
@@ -220,9 +220,7 @@ class Partition(object):
         msger.debug("Added %d extra blocks to %s to get to %d total blocks" % \
                     (extra_blocks, self.mountpoint, rootfs_size))
 
-        dd_cmd = "dd if=/dev/zero of=%s bs=1024 seek=%d count=0 bs=1k" % \
-            (rootfs, rootfs_size)
-        exec_cmd(dd_cmd)
+        exec_cmd("truncate %s -s %d" % (rootfs, rootfs_size * 1024))
 
         extra_imagecmd = "-i 8192"
 
@@ -255,9 +253,7 @@ class Partition(object):
         msger.debug("Added %d extra blocks to %s to get to %d total blocks" % \
                     (extra_blocks, self.mountpoint, rootfs_size))
 
-        dd_cmd = "dd if=/dev/zero of=%s bs=1024 seek=%d count=0 bs=1k" % \
-            (rootfs, rootfs_size)
-        exec_cmd(dd_cmd)
+        exec_cmd("truncate %s -s %d" % (rootfs, rootfs_size * 1024))
 
         label_str = ""
         if self.label:
@@ -320,9 +316,7 @@ class Partition(object):
         """
         Prepare an empty ext2/3/4 partition.
         """
-        dd_cmd = "dd if=/dev/zero of=%s bs=1k seek=%d count=0" % \
-            (rootfs, self.size)
-        exec_cmd(dd_cmd)
+        exec_cmd("truncate %s -s %d" % (rootfs, self.size * 1024))
 
         extra_imagecmd = "-i 8192"
 
@@ -339,9 +333,7 @@ class Partition(object):
         """
         Prepare an empty btrfs partition.
         """
-        dd_cmd = "dd if=/dev/zero of=%s bs=1k seek=%d count=0" % \
-            (rootfs, self.size)
-        exec_cmd(dd_cmd)
+        exec_cmd("truncate %s -s %d" % (rootfs, self.size * 1024))
 
         label_str = ""
         if self.label:
@@ -402,9 +394,7 @@ class Partition(object):
         """
         path = "%s/fs.%s" % (cr_workdir, self.fstype)
 
-        dd_cmd = "dd if=/dev/zero of=%s bs=1k seek=%d count=0" % \
-            (path, self.size)
-        exec_cmd(dd_cmd)
+        exec_cmd("truncate %s -s %d" % (path, self.size * 1024))
 
         import uuid
         label_str = ""
diff --git a/scripts/lib/wic/utils/fs_related.py b/scripts/lib/wic/utils/fs_related.py
index 2e74461a40..2658dcfc20 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