Add checksum to verify_header

Currently we don't know if the verify_header itself is
valid when pulled off a disk. While it will fail verify
if it is, fio might then confuse the 'expected' and
'received' data since it re-generates the corrupted
crc with the seed stored. But if the seed is corrupt,
then we fail.

So checksum the verify header, so that we know for a fact
whether the header is valid or not.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/verify.h b/verify.h
index 49ce417..ec7365c 100644
--- a/verify.h
+++ b/verify.h
@@ -4,6 +4,7 @@
 #include <stdint.h>
 
 #define FIO_HDR_MAGIC	0xf00baaef
+#define FIO_HDR_MAGIC2	0xf00dbeef
 
 enum {
 	VERIFY_NONE = 0,		/* no verification */
@@ -28,10 +29,13 @@
  * data.
  */
 struct verify_header {
-	unsigned int fio_magic;
-	unsigned int len;
-	unsigned int verify_type;
-	unsigned long rand_seed;
+	uint32_t fio_magic;
+	uint32_t len;
+	uint32_t verify_type;
+	uint32_t pad1;
+	uint64_t rand_seed;
+	uint32_t pad2;
+	uint32_t crc32;
 };
 
 struct vhdr_md5 {