wic/filemap: If FIGETBSZ iotctl fail, failback to os.stat

Some file systems don't support fetching the block size (notably the
file system Docker uses for containers), so if iotctl() fail, try to use
failback via os.stat() to get block size.

(From OE-Core rev: e219f5175177a640dd62833082ea19adc1c13d42)

Signed-off-by: Kalle lampila <kalle.lampila@lempea.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/lib/wic/filemap.py

@@ -34,9 +34,11 @@ def get_block_size(file_obj):
     # the FIGETBSZ ioctl (number 2).
     try:
         binary_data = fcntl.ioctl(file_obj, 2, struct.pack('I', 0))
+        bsize = struct.unpack('I', binary_data)[0]
     except OSError:
-        raise IOError("Unable to determine block size")
-    bsize = struct.unpack('I', binary_data)[0]
+        bsize = None
+
+    # If ioctl causes OSError or give bsize to zero failback to os.fstat
     if not bsize:
         import os
         stat = os.fstat(file_obj.fileno())