Open target device with O_SYNC

Open the target device with the O_SYNC flag; in this way, the data for
each range will be flushed to the device before starting processing the
next one.

As a side effect, the application will return immediately after an error
instead of waiting for all the previous cached writes to be sync'ed to
the target device.

Signed-off-by: Francesco Valla <[email protected]>

bmap-writer.cpp

@@ -193,7 +193,7 @@ int BmapWriteImage(const std::string &imageFile, const bmap_t &bmap, const std::
     int ret = 0;
 
     try {
-        dev_fd = open(device.c_str(), O_WRONLY | O_CREAT, S_IRUSR | S_IWUSR);
+        dev_fd = open(device.c_str(), O_WRONLY | O_CREAT | O_SYNC, S_IRUSR | S_IWUSR);
         if (dev_fd < 0) {
             throw std::string("Unable to open or create target device");
         }