[gnome-continuous-yocto/gnomeostree-3.28-rocko: 81/8267] wic: add sparse_copy API

[Emmanuele Bassi <ebassi src gnome org>]

commit 4b971568e142952aa4c71ebc7a1f5326717ff210
Author: Ed Bartosh <ed bartosh linux intel com>
Date:   Thu Apr 28 13:58:09 2016 +0300

    wic: add sparse_copy API
    
    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]
    
    (From OE-Core rev: bfde62bdc03152a4d3d383512479b974fa867f94)
    
    Signed-off-by: Ed Bartosh <ed bartosh linux intel com>
    Signed-off-by: Richard Purdie <richard purdie linuxfoundation org>

 scripts/lib/wic/filemap.py |   30 ++++++++++++++++++++++++++++++
 1 files changed, 30 insertions(+), 0 deletions(-)
---
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()