Don't look for GPT primary and secondary tables on a disk unless we have

a valid PMBR.  Without this fix, if label a disk with a GPT, then relabel
it with an MBR the GPT tables are still present.  If you then try to create
a GPT with 'gpt create', gpt(8) will fail to open the device because the
partitions in the stale GPT overlap with the slices in the MBR.

MFC after:	1 week

1 files changed, 10 insertions, 4 deletions

diff --git a/sbin/gpt/gpt.c b/sbin/gpt/gpt.c
index 7a76f6d..6085ed2 100644
--- a/sbin/gpt/gpt.c
+++ b/sbin/gpt/gpt.c
@@ -585,10 +585,16 @@ gpt_open(const char *dev)
 
 	if (gpt_mbr(fd, 0LL) == -1)
 		goto close;
-	if (gpt_gpt(fd, 1LL) == -1)
-		goto close;
-	if (gpt_gpt(fd, mediasz / secsz - 1LL) == -1)
-		goto close;
+
+	/*
+	 * Don't look for a GPT unless we have a valid PMBR.
+	 */
+	if (map_find(MAP_TYPE_PMBR) != NULL) {
+		if (gpt_gpt(fd, 1LL) == -1)
+			goto close;
+		if (gpt_gpt(fd, mediasz / secsz - 1LL) == -1)
+			goto close;
+	}
 
 	return (fd);