image_types_sparse: Pad source image to block size

If the source image's size is not aligned to the sparse image's block
size, then conversion will fail with

img2simg: libsparse/sparse.cpp:133: int write_all_blocks(sparse_file*, output_file*): Assertion `pad >= 0' failed.

This is a bug in img2simg, but an easy way to work around it is to pad
the source image ourselves. The default block size of 4096 matches
img2simg's default block size.

Signed-off-by: Sean Anderson <sean.anderson@seco.com>
Signed-off-by: Khem Raj <raj.khem@gmail.com>

1 files changed, 12 insertions, 4 deletions

diff --git a/meta-oe/classes/image_types_sparse.bbclass b/meta-oe/classes/image_types_sparse.bbclass
index 4263593a8d..355a3dafc2 100644
--- a/meta-oe/classes/image_types_sparse.bbclass
+++ b/meta-oe/classes/image_types_sparse.bbclass
@@ -1,8 +1,16 @@
 inherit image_types
 
+# This sets the granularity of the sparse image conversion. Chunk sizes will be
+# specified in units of this value. Setting this value smaller than the
+# underlying image's block size will not result in any further space saving.
+# However, there is no loss in correctness if this value is larger or smaller
+# than optimal. This value should be a power of two.
+SPARSE_BLOCK_SIZE ??= "4096"
+
 CONVERSIONTYPES += "sparse"
-CONVERSION_CMD:sparse = " \
-    img2simg "${IMAGE_NAME}${IMAGE_NAME_SUFFIX}.${type}" \
-             "${IMAGE_NAME}${IMAGE_NAME_SUFFIX}.${type}.sparse" \
-"
+CONVERSION_CMD:sparse() {
+    INPUT="${IMAGE_NAME}${IMAGE_NAME_SUFFIX}.${type}"
+    truncate --no-create --size=%${SPARSE_BLOCK_SIZE} "$INPUT"
+    img2simg "$INPUT" "$INPUT.sparse" ${SPARSE_BLOCK_SIZE}
+}
 CONVERSION_DEPENDS_sparse = "android-tools-native"