From ff3bed806863d1c2075d0efda70b39ea6af9ecba Mon Sep 17 00:00:00 2001
From: Karel Zak <kzak@redhat.com>
Date: Thu, 12 Mar 2009 16:01:59 +0100
Subject: [PATCH] mkswap: zap bootbits

/dev/sdb1 originally initialized by cryptsetup:

and OLD mkswap:

        # vol_id /dev/sdb1 | grep TYPE
        ID_FS_TYPE=swap

        # blkid -s TYPE /dev/sdb1
        /dev/sdb1: TYPE="crypt_LUKS"

So, we have two different *valid* signatures on the device now!

NEW mkswap:

        # blkid -s TYPE /dev/sdb1
        /dev/sdb1: TYPE="swap"

        # /lib/udev/vol_id /dev/sdb1 | grep TYPE
        ID_FS_TYPE=swap

the bootbits (first 1024 bytes) was erased.

We shouldn't zap disk labels (BSD, SUN, ...) and boot loaders (on whole
disk):

        # mkswap  /dev/sdb2
        mkswap: /dev/sdb2: warning: don't erase bootbits sectors
                (BSD partition table detected). Use -f to force.
        Setting up swapspace version 1, size = 4348 KiB
        no label, UUID=69d87cef-71ac-4fb0-a689-ce3e930dea17

        # mkswap  /dev/sdb
        mkswap: /dev/sdb: warning: don't erase bootbits sectors
                on whole disk. Use -f to force.
        Setting up swapspace version 1, size = 8188 KiB
        no label, UUID=97757ad7-8a84-43d9-bcb4-16fefd93a2ac

Signed-off-by: Karel Zak <kzak@redhat.com>
---
 disk-utils/Makefile.am |  2 +-
 disk-utils/mkswap.c    | 45 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 46 insertions(+), 1 deletion(-)

diff --git a/disk-utils/Makefile.am b/disk-utils/Makefile.am
index 9e9db95b..4854d5f6 100644
--- a/disk-utils/Makefile.am
+++ b/disk-utils/Makefile.am
@@ -12,7 +12,7 @@ sbin_PROGRAMS = mkfs mkswap fsck.minix mkfs.minix mkfs.bfs
 fsck_minix_SOURCES = fsck.minix.c minix.h
 mkfs_minix_SOURCES = mkfs.minix.c minix.h $(utils_common)
 mkfs_bfs_SOURCES = mkfs.bfs.c $(utils_common)
-mkswap_SOURCES = mkswap.c $(utils_common)
+mkswap_SOURCES = mkswap.c $(utils_common) ../lib/wholedisk.c ../lib/pttype.c
 
 usrbinexec_PROGRAMS = isosize
 usrsbinexec_PROGRAMS =
diff --git a/disk-utils/mkswap.c b/disk-utils/mkswap.c
index 6e151af3..4acc73b2 100644
--- a/disk-utils/mkswap.c
+++ b/disk-utils/mkswap.c
@@ -53,6 +53,8 @@
 #include "nls.h"
 #include "blkdev.h"
 #include "pathnames.h"
+#include "pttype.h"
+#include "wholedisk.h"
 
 #ifdef HAVE_LIBUUID
 #include <uuid/uuid.h>
@@ -379,6 +381,47 @@ write_all(int fd, const void *buf, size_t count) {
 	return 0;
 }
 
+static void
+zap_bootbits(int fd, const char *devname, int force)
+{
+	const char *type = NULL;
+	int zap = 1;
+
+	if (!force) {
+		if (lseek(fd, 0, SEEK_SET) != 0)
+	                die(_("unable to rewind swap-device"));
+
+		if (is_whole_disk_fd(fd, devname))
+			/* don't zap bootbits on whole disk -- we know nothing
+			 * about bootloaders on the device */
+			zap = 0;
+
+		else if ((type = get_pt_type_fd(fd)))
+			/* don't zap partition table */
+			zap = 0;
+	}
+
+	if (zap) {
+		char buf[1024];
+
+		if (lseek(fd, 0, SEEK_SET) != 0)
+	                die(_("unable to rewind swap-device"));
+
+		memset(buf, 0, sizeof(buf));
+		if (write_all(fd, buf, sizeof(buf)))
+			die(_("unable to erase bootbits sectors"));
+		return;
+	}
+
+	fprintf(stderr, _("%s: %s: warning: don't erase bootbits sectors\n"),
+		program_name, devname);
+	if (type)
+		fprintf(stderr, _("        (%s partition table detected). "), type);
+	else
+		fprintf(stderr, _("        on whole disk. "));
+	fprintf(stderr, "Use -f to force.\n");
+}
+
 int
 main(int argc, char ** argv) {
 	struct stat statbuf;
@@ -561,6 +604,8 @@ main(int argc, char ** argv) {
 	if (check)
 		check_blocks();
 
+	zap_bootbits(DEV, device_name, force);
+
 	p->version = 1;
 	p->last_page = PAGES-1;
 	p->nr_badpages = badpages;
-- 
2.39.5