vpc: Fail open on bad header checksum

vpc_open() merely prints a warning when it finds a bad header
checksum.  Turn that into a hard error.

Cc: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>
Message-Id: <20181017082702.5581-39-armbru@redhat.com>
[Error message capitalized for local consistency]
Reviewed-by: NKevin Wolf <kwolf@redhat.com>

block/vpc.c

@@ -284,9 +284,11 @@ static int vpc_open(BlockDriverState *bs, QDict *options, int flags,
 
     checksum = be32_to_cpu(footer->checksum);
     footer->checksum = 0;
-    if (vpc_checksum(s->footer_buf, HEADER_SIZE) != checksum)
-        fprintf(stderr, "block-vpc: The header checksum of '%s' is "
-            "incorrect.\n", bs->filename);
+    if (vpc_checksum(s->footer_buf, HEADER_SIZE) != checksum) {
+        error_setg(errp, "Incorrect header checksum");
+        ret = -EINVAL;
+        goto fail;
+    }
 
     /* Write 'checksum' back to footer, or else will leave it with zero. */
     footer->checksum = cpu_to_be32(checksum);