Flush block device with ioctl before reading it back

writeimg.c

@@ -11,6 +11,11 @@
 #include <sys/stat.h>
 #include <unistd.h>
 
+#if __linux__
+#include <linux/fs.h>  /* IOTCL flush number */
+#include <sys/ioctl.h> /* IOCTL */
+#endif
+
 #ifndef GITREV
 #define GITREV "unknown"
 #endif
@@ -142,6 +147,9 @@ int perform_write(write_job_t *job) {
     memset(job->buffer, 0, BLOCKSIZE);
     memset(job->buffer2, 0, BLOCKSIZE);
 
+    /* This is essentially $ blockdev --flushbufs */
+    ioctl(block_fd, BLKFLSBUF);
+
     int crc_back = crc32_init();
     b_written = 0;