From b8671fe76370436beb37ca65ea1563c3284a2699 Mon Sep 17 00:00:00 2001
From: Karel Zak <kzak@redhat.com>
Date: Wed, 27 May 2020 16:58:08 +0200
Subject: [PATCH] mkswap: add --lock and LOCK_BLOCK_DEVICE

Addresses: https://github.com/karelzak/util-linux/issues/921
Signed-off-by: Karel Zak <kzak@redhat.com>
---
 disk-utils/mkswap.8 | 10 ++++++++++
 disk-utils/mkswap.c | 20 ++++++++++++++++++++
 2 files changed, 30 insertions(+)

diff --git a/disk-utils/mkswap.8 b/disk-utils/mkswap.8
index 81ad133b4f..a8cbcc20ae 100644
--- a/disk-utils/mkswap.8
+++ b/disk-utils/mkswap.8
@@ -76,6 +76,14 @@ Specify a \fIlabel\fR for the device, to allow
 .B swapon
 by label.
 .TP
+\fB\-\-lock\fR[=\fImode\fR]
+Use exclusive BSD lock for device or file it operates.  The optional argument
+\fImode\fP can be \fByes\fR, \fBno\fR (or 1 and 0) or \fBnonblock\fR.  If the \fImode\fR
+argument is omitted, it defaults to \fB"yes"\fR.  This option overwrites
+environment variable \fB$LOCK_BLOCK_DEVICE\fR.  The default is not to use any
+lock at all, but it's recommended to avoid collisions with udevd or other
+tools.
+.TP
 .BR \-p , " \-\-pagesize " \fIsize\fR
 Specify the page \fIsize\fR (in bytes) to use.  This option is usually unnecessary;
 .B mkswap
@@ -102,6 +110,8 @@ Display version information and exit.
 .SH ENVIRONMENT
 .IP LIBBLKID_DEBUG=all
 enables libblkid debug output.
+.IP LOCK_BLOCK_DEVICE=<mode>
+use exclusive BSD lock.  The mode is "1" or "0".  See \fB\-\-lock\fR for more details.
 
 .SH NOTES
 The maximum useful size of a swap area depends on the architecture and
diff --git a/disk-utils/mkswap.c b/disk-utils/mkswap.c
index c6aaaf5f1b..4fb8415362 100644
--- a/disk-utils/mkswap.c
+++ b/disk-utils/mkswap.c
@@ -53,6 +53,7 @@ struct mkswap_control {
 	void			*signature_page;/* buffer with swap header */
 
 	char			*devname;	/* device or file name */
+	const char		*lockmode;	/* as specified by --lock */
 	struct stat		devstat;	/* stat() result */
 	int			fd;		/* swap file descriptor */
 
@@ -161,6 +162,8 @@ static void __attribute__((__noreturn__)) usage(void)
 		" -v, --swapversion NUM     specify swap-space version number\n"
 		" -U, --uuid UUID           specify the uuid to use\n"
 		));
+	fprintf(out,
+	      _("     --lock[=<mode>]       use exclusive device lock (%s, %s or %s)\n"), "yes", "no", "nonblock");
 	printf(USAGE_HELP_OPTIONS(27));
 
 	printf(USAGE_MAN_TAIL("mkswap(8)"));
@@ -244,6 +247,10 @@ static void open_device(struct mkswap_control *ctl)
 	ctl->fd = open_blkdev_or_file(&ctl->devstat, ctl->devname, O_RDWR);
 	if (ctl->fd < 0)
 		err(EXIT_FAILURE, _("cannot open %s"), ctl->devname);
+
+	if (blkdev_lock(ctl->fd, ctl->devname, ctl->lockmode) != 0)
+		exit(EXIT_FAILURE);
+
 	if (ctl->check && S_ISREG(ctl->devstat.st_mode)) {
 		ctl->check = 0;
 		warnx(_("warning: checking bad blocks from swap file is not supported: %s"),
@@ -354,6 +361,9 @@ int main(int argc, char **argv)
 	const char *opt_uuid = NULL;
 	uuid_t uuid_dat;
 #endif
+	enum {
+		OPT_LOCK = CHAR_MAX + 1,
+	};
 	static const struct option longopts[] = {
 		{ "check",       no_argument,       NULL, 'c' },
 		{ "force",       no_argument,       NULL, 'f' },
@@ -363,6 +373,7 @@ int main(int argc, char **argv)
 		{ "uuid",        required_argument, NULL, 'U' },
 		{ "version",     no_argument,       NULL, 'V' },
 		{ "help",        no_argument,       NULL, 'h' },
+		{ "lock",        optional_argument, NULL, OPT_LOCK },
 		{ NULL,          0, NULL, 0 }
 	};
 
@@ -401,6 +412,15 @@ int main(int argc, char **argv)
 			break;
 		case 'V':
 			print_version(EXIT_SUCCESS);
+			break;
+		case OPT_LOCK:
+			ctl.lockmode = "1";
+			if (optarg) {
+				if (*optarg == '=')
+					optarg++;
+				ctl.lockmode = optarg;
+			}
+			break;
 		case 'h':
 			usage();
 		default:
-- 
2.47.2