[OE-core] [wic][PATCH v2 6/8] wic: add sparse_copy API

[Ed Bartosh]

In order to make wic images sparse sparse_copy function has been
copied from meta-ostro:
https://github.com/kad/meta-ostro/blob/master/meta-ostro/lib/image-dsk.py
This function uses filemap APIs to copy source sparse file into
destination file preserving sparseness.

The function has been modified to satisfy wic requirements:
parameter 'skip' has been added.

[YOCTO #9099]

Signed-off-by: Ed Bartosh <ed.bartosh at linux.intel.com>
---
 scripts/lib/wic/filemap.py | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/scripts/lib/wic/filemap.py b/scripts/lib/wic/filemap.py
index 1d04328..f8b2ba7 100644
--- a/scripts/lib/wic/filemap.py
+++ b/scripts/lib/wic/filemap.py
@@ -529,3 +529,33 @@ def filemap(image, log=None):
         return FilemapFiemap(image, log)
     except ErrorNotSupp:
         return FilemapSeek(image, log)
+
+def sparse_copy(src_fname, dst_fname, offset=0, skip=0):
+    """Efficiently copy sparse file to or into another file."""
+    fmap = filemap(src_fname)
+    try:
+        dst_file = open(dst_fname, 'r+b')
+    except IOError:
+        dst_file = open(dst_fname, 'wb')
+
+    for first, last in fmap.get_mapped_ranges(0, fmap.blocks_cnt):
+        start = first * fmap.block_size
+        end = (last + 1) * fmap.block_size
+
+        if start < skip < end:
+            start = skip
+
+        fmap._f_image.seek(start, os.SEEK_SET)
+        dst_file.seek(offset + start, os.SEEK_SET)
+
+        chunk_size = 1024 * 1024
+        to_read = end - start
+        read = 0
+
+        while read < to_read:
+            if read + chunk_size > to_read:
+                chunk_size = to_read - read
+            chunk = fmap._f_image.read(chunk_size)
+            dst_file.write(chunk)
+            read += chunk_size
+    dst_file.close()
-- 
2.1.4