From f907c64a8f477b582a58d1eaaa229a5fa39ff876 Mon Sep 17 00:00:00 2001
From: jmcneill <jmcneill@NetBSD.org>
Date: Sun, 24 May 2020 18:42:48 +0000
Subject: [PATCH] Add -g flag to preserve GPT headers when updating MBR.

---
 sbin/fdisk/fdisk.8 | 12 ++++++++----
 sbin/fdisk/fdisk.c | 13 ++++++++++---
 2 files changed, 18 insertions(+), 7 deletions(-)

diff --git a/sbin/fdisk/fdisk.8 b/sbin/fdisk/fdisk.8
index 0c8f49799a7c..86dbcdbde5d8 100644
--- a/sbin/fdisk/fdisk.8
+++ b/sbin/fdisk/fdisk.8
@@ -1,6 +1,6 @@
-.\"	$NetBSD: fdisk.8,v 1.90 2019/12/15 11:49:28 wiz Exp $
+.\"	$NetBSD: fdisk.8,v 1.91 2020/05/24 18:42:48 jmcneill Exp $
 .\"
-.Dd December 14, 2019
+.Dd May 24, 2020
 .Dt FDISK 8
 .Os
 .Sh NAME
@@ -8,7 +8,7 @@
 .Nd MS-DOS partition maintenance program
 .Sh SYNOPSIS
 .Nm
-.Op Fl aBFfIiSuv
+.Op Fl aBFfgIiSuv
 .Oo
 .Fl 0 | 1 | 2 | 3 | E Ar number
 .Op Fl s Oo Ar id Oc Ns Oo / Ns Oo Ar start Oc Ns Oo / Ns Oo Ar size Oc Ns Oo / Ns Oo Ar bootmenu Oc Oc Oc Oc
@@ -114,7 +114,9 @@ selects defaults for its questions to guarantee that behaviour.
 If partition data is going to be updated and the disk carries GUID Partition
 Tables,
 .Nm
-will remove both primary and backup GPT headers from the disk.
+will remove both primary and backup GPT headers from the disk unless the
+.Fl g
+flag is specified.
 See
 .Xr gpt 8
 for information on how to manipulate GUID Partition Tables.
@@ -262,6 +264,8 @@ and
 fields
 .Pq only Ar start No and Ar size No can be specified by Fl s No option .
 They will be automatically computed using the BIOS geometry.
+.It Fl g
+Preserve existing GPT headers when updating partitions.
 .It Fl I
 Ignore errors from overlapping partitions.
 Some devices (cameras CHDK) require overlapping partitions to support
diff --git a/sbin/fdisk/fdisk.c b/sbin/fdisk/fdisk.c
index 461f8854a2a4..02b36f785c22 100644
--- a/sbin/fdisk/fdisk.c
+++ b/sbin/fdisk/fdisk.c
@@ -1,4 +1,4 @@
-/*	$NetBSD: fdisk.c,v 1.157 2019/10/07 20:56:07 christos Exp $ */
+/*	$NetBSD: fdisk.c,v 1.158 2020/05/24 18:42:48 jmcneill Exp $ */
 
 /*
  * Mach Operating System
@@ -39,7 +39,7 @@
 #include <sys/cdefs.h>
 
 #ifndef lint
-__RCSID("$NetBSD: fdisk.c,v 1.157 2019/10/07 20:56:07 christos Exp $");
+__RCSID("$NetBSD: fdisk.c,v 1.158 2020/05/24 18:42:48 jmcneill Exp $");
 #endif /* not lint */
 
 #define MBRPTYPENAMES
@@ -141,7 +141,7 @@ static char *boot_path = NULL;			/* name of file we actually opened */
 #define BOOTSEL_OPTIONS	
 #define change_part(e, p, id, st, sz, bm) change__part(e, p, id, st, sz)
 #endif
-#define OPTIONS	BOOTSEL_OPTIONS "0123FSafiIluvA:b:c:E:r:s:w:z:"
+#define OPTIONS	BOOTSEL_OPTIONS "0123FSafgiIluvA:b:c:E:r:s:w:z:"
 
 /*
  * Disk geometry and partition alignment.
@@ -215,6 +215,7 @@ static int u_flag;		/* update partition data */
 static int v_flag;		/* more verbose */
 static int sh_flag;		/* Output data as shell defines */
 static int f_flag;		/* force --not interactive */
+static int g_flag;		/* preserve GPT headers */
 static int s_flag;		/* set id,offset,size */
 static int b_flag;		/* Set cyl, heads, secs (as c/h/s) */
 static int B_flag;		/* Edit/install bootselect code */
@@ -430,6 +431,9 @@ main(int argc, char *argv[])
 		case 'f':	/* Non interactive */
 			f_flag = 1;
 			break;
+		case 'g':	/* Preserve GPT headers */
+			g_flag = 1;
+			break;
 		case 'i':	/* Always update bootcode */
 			i_flag = 1;
 			break;
@@ -3058,6 +3062,9 @@ delete_gpt(struct gpt_hdr *gptp)
 	char buf[512];
 	struct gpt_hdr *hdr = (void *)buf;
 
+	if (g_flag)
+		return 0;	/* preserve existing GPT headers */
+
 	if (gptp->hdr_size == 0)
 		return 0;