Remove unnecessary sync calls from build_image and image_to_vm.sh.

Calling sync in build scripts pauses the build unnecessarily, particularly
when other steps are running in parallel.

BUG=chromium-os:19150
TEST=Run cbuildbot release build and watch faster performance.

Change-Id: Ia2469e3be68fdd38474ab4e6f67b06339c04822f
Reviewed-on: http://gerrit.chromium.org/gerrit/5966
Reviewed-by: Thieu Le <thieule@chromium.org>
Reviewed-by: Richard Barnette <jrbarnette@chromium.org>
Reviewed-by: <taysom@google.com>
Tested-by: David James <davidjames@chromium.org>

build_image

@@ -458,10 +458,7 @@ zero_free_space() {
   # dd is a silly thing and will produce a "No space left on device" message
   # that cannot be turned off and is confusing to unsuspecting victims.
   ( sudo dd if=/dev/zero of="${fs_mount_point}/filler" bs=4096 \
-    || true ) 2>&1 |grep -v "No space left on device"
-  sudo sync
-  sudo rm -f "${fs_mount_point}/filler"
-  sudo sync
+    || true ) 2>&1 | grep -v "No space left on device"
 }
 
 create_base_image() {
@@ -627,6 +624,13 @@ create_base_image() {
 
   trap delete_prompt EXIT
 
+  # Now that the filler file has been sync'd to disk and has filled up all free
+  # space with zeros, re-mount the rootfs to delete the filler file.
+  LOOP_DEV=$(sudo losetup --show -f "${ROOT_FS_IMG}")
+  sudo mount -t ext2 "${LOOP_DEV}" "${ROOT_FS_DIR}"
+  sudo rm -f "${ROOT_FS_DIR}/filler"
+  sudo umount -d "${ROOT_FS_DIR}"
+
   # Create the GPT-formatted image.
   build_gpt "${OUTPUT_DIR}/${image_name}" \
             "${ROOT_FS_IMG}" \

image_to_vm.sh

@@ -166,7 +166,6 @@ else
     fi
     sudo e2fsck -pf "${STATEFUL_LOOP_DEV}"
     sudo resize2fs "${STATEFUL_LOOP_DEV}"
-    sync
     sudo losetup -d "${STATEFUL_LOOP_DEV}"
   fi
 fi
@@ -194,7 +193,6 @@ sudo python "${SCRIPTS_DIR}/fixup_image_for_qemu.py" \
 sudo sed -i -e 's/sdb3/sda3/g' "${TEMP_MNT}/boot/syslinux/usb.A.cfg"
 
 # Unmount everything prior to building a final image
-sync
 trap - INT TERM EXIT
 cleanup