Make GPT_read() obtain and validate the on-disk MBR itself, via

MBR_read(), and report success/failure.

Simplifies logic and makes clearer that the protective MBR is a
required part of a GPT.

With the standardization on 0/-1 return values for helper
functions, rename 'valid' to 'error' in GPT_read() to make logic
less mind bending.

No functional change.

4 files changed, 34 insertions, 38 deletions

diff --git a/sbin/fdisk/fdisk.c b/sbin/fdisk/fdisk.c
index 22e2448cf4a..b92c4e12268 100644
--- a/sbin/fdisk/fdisk.c
+++ b/sbin/fdisk/fdisk.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: fdisk.c,v 1.125 2021/07/18 12:41:00 krw Exp $	*/
+/*	$OpenBSD: fdisk.c,v 1.126 2021/07/18 15:28:37 krw Exp $	*/
 
 /*
  * Copyright (c) 1997 Tobias Weingartner
@@ -167,11 +167,6 @@ main(int argc, char *argv[])
 	if (error)
 		errx(1, "Can't read MBR!");
 
-	/* Get the GPT if present. Either primary or secondary is ok. */
-	efi = MBR_protective_mbr(&mbr);
-	if (efi != -1)
-		GPT_read(ANYGPT);
-
 	/* Create initial/default MBR. */
 	if (mbrfile == NULL) {
 		memcpy(&dos_mbr, builtin_mbr, sizeof(dos_mbr));
@@ -195,7 +190,7 @@ main(int argc, char *argv[])
 
 	query = NULL;
 	if (A_flag) {
-		if (letoh64(gh.gh_sig) != GPTSIGNATURE)
+		if (GPT_read(ANYGPT))
 			errx(1, "-A requires a valid GPT");
 		else {
 			initial_mbr = mbr;	/* Keep current MBR. */
diff --git a/sbin/fdisk/gpt.c b/sbin/fdisk/gpt.c
index 3ed8662cc61..0252b7f83f7 100644
--- a/sbin/fdisk/gpt.c
+++ b/sbin/fdisk/gpt.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: gpt.c,v 1.45 2021/07/16 13:29:49 krw Exp $	*/
+/*	$OpenBSD: gpt.c,v 1.46 2021/07/18 15:28:37 krw Exp $	*/
 /*
  * Copyright (c) 2015 Markus Muller <mmu@grummel.net>
  * Copyright (c) 2015 Kenneth R Westerback <krw@openbsd.org>
@@ -30,6 +30,7 @@
 
 #include "part.h"
 #include "disk.h"
+#include "mbr.h"
 #include "misc.h"
 #include "gpt.h"
 
@@ -202,35 +203,45 @@ get_partition_table(void)
 	return 0;
 }
 
-void
+int
 GPT_read(const int which)
 {
-	int			valid;
+	struct mbr		mbr;
+	int			error;
+
+	error = MBR_read(0, 0, &mbr);
+	if (error == 0)
+		error = MBR_protective_mbr(&mbr);
+	if (error)
+		goto done;
 
 	switch (which) {
 	case PRIMARYGPT:
-		valid = get_header(GPTSECTOR);
+		error = get_header(GPTSECTOR);
 		break;
 	case SECONDARYGPT:
-		valid = get_header(DL_GETDSIZE(&dl) - 1);
+		error = get_header(DL_GETDSIZE(&dl) - 1);
 		break;
 	case ANYGPT:
-		valid = get_header(GPTSECTOR);
-		if (valid != 0 || get_partition_table() != 0)
-			valid = get_header(DL_GETDSIZE(&dl) - 1);
+		error = get_header(GPTSECTOR);
+		if (error != 0 || get_partition_table() != 0)
+			error = get_header(DL_GETDSIZE(&dl) - 1);
 		break;
 	default:
-		return;
+		return -1;
 	}
 
-	if (valid == 0)
-		valid = get_partition_table();
+	if (error == 0)
+		error = get_partition_table();
 
-	if (valid != 0) {
+ done:
+	if (error != 0) {
 		/* No valid GPT found. Zap any artifacts. */
 		memset(&gh, 0, sizeof(gh));
 		memset(&gp, 0, sizeof(gp));
 	}
+
+	return error;
 }
 
 void
diff --git a/sbin/fdisk/gpt.h b/sbin/fdisk/gpt.h
index 0ea4968f42b..ada2b3356f7 100644
--- a/sbin/fdisk/gpt.h
+++ b/sbin/fdisk/gpt.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: gpt.h,v 1.16 2021/07/15 21:58:02 krw Exp $	*/
+/*	$OpenBSD: gpt.h,v 1.17 2021/07/18 15:28:37 krw Exp $	*/
 /*
  * Copyright (c) 2015 Markus Muller <mmu@grummel.net>
  * Copyright (c) 2015 Kenneth R Westerback <krw@openbsd.org>
@@ -16,7 +16,7 @@
  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
 
-void		GPT_read(const int);
+int		GPT_read(const int);
 int		GPT_get_lba_start(const unsigned int);
 int		GPT_get_lba_end(const unsigned int);
 
diff --git a/sbin/fdisk/user.c b/sbin/fdisk/user.c
index af5ac347df0..cd8b8ea606f 100644
--- a/sbin/fdisk/user.c
+++ b/sbin/fdisk/user.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: user.c,v 1.64 2021/07/18 12:41:00 krw Exp $	*/
+/*	$OpenBSD: user.c,v 1.65 2021/07/18 15:28:37 krw Exp $	*/
 
 /*
  * Copyright (c) 1997 Tobias Weingartner
@@ -73,13 +73,8 @@ USER_edit(const uint64_t lba_self, const uint64_t lba_firstembr)
 	if (error == -1)
 		goto done;
 
-	if (editlevel == 1) {
-		memset(&gh, 0, sizeof(gh));
-		memset(&gp, 0, sizeof(gp));
-		efi = MBR_protective_mbr(&mbr);
-		if (efi != -1)
-			GPT_read(ANYGPT);
-	}
+	if (editlevel == 1)
+		GPT_read(ANYGPT);
 
 	printf("Enter 'help' for information\n");
 
@@ -140,7 +135,7 @@ USER_print_disk(const int verbosity)
 {
 	struct mbr		mbr;
 	uint64_t		lba_self, lba_firstembr;
-	int			i, efi, error;
+	int			i, error;
 
 	lba_self = lba_firstembr = 0;
 
@@ -149,19 +144,14 @@ USER_print_disk(const int verbosity)
 		if (error == -1)
 			break;
 		if (lba_self == 0) {
-			efi = MBR_protective_mbr(&mbr);
-			if (efi == -1) {
-				/* No valid 0xEE partition means no GPT. */
+			if (GPT_read(ANYGPT)) {
 				if (verbosity == VERBOSE) {
 					printf("Primary GPT:\nNot Found\n");
 					printf("\nSecondary GPT:\nNot Found\n");
 				}
 			} else if (verbosity == TERSE) {
-				/* Should already have read one of Primary/Secondary GPT. */
-				if (letoh64(gh.gh_sig) == GPTSIGNATURE) {
-					GPT_print("s", verbosity);
-					return;
-				}
+				GPT_print("s", verbosity);
+				return;
 			} else {
 				/*. Read & print both primary and secondary GPT. */
 				printf("Primary GPT:\n");