mountpoint: add --nofollow option

The no follow option will allow user to distinct mount points from symbolic
links pointing to them.  Arguably this is pretty pedantic option, mounting a
device or bind mount to a directory via symlink does not have or cause any
issues.

Addresses: https://github.com/karelzak/util-linux/issues/832
Signed-off-by: Sami Kerola <kerolasa@iki.fi>

bash-completion/mountpoint

@@ -11,7 +11,7 @@ _mountpoint_module()
 	esac
 	case $cur in
 		-*)
-			OPTS="--quiet --fs-devno --devno --help --version"
+			OPTS="--quiet --nofollow --fs-devno --devno --help --version"
 			COMPREPLY=( $(compgen -W "${OPTS[*]}" -- $cur) )
 			return 0
 			;;

sys-utils/mountpoint.1

@@ -1,4 +1,4 @@
-.TH MOUNTPOINT 1 "July 2014" "util-linux" "User Commands"
+.TH MOUNTPOINT 1 "August 2019" "util-linux" "User Commands"
 .SH NAME
 mountpoint \- see if a directory or file is a mountpoint
 .SH SYNOPSIS
@@ -28,6 +28,11 @@ directory.
 .BR \-q , " \-\-quiet"
 Be quiet - don't print anything.
 .TP
+.B "\-\-nofollow"
+Do not follow symbolic link if it the last elemnt of the
+.I directory
+path.
+.TP
 .BR \-x , " \-\-devno"
 Show the major/minor numbers of the given blockdevice on standard output.
 .TP

sys-utils/mountpoint.c

@@ -47,6 +47,7 @@ struct mountpoint_control {
 	unsigned int
 		dev_devno:1,
 		fs_devno:1,
+		nofollow:1,
 		quiet:1;
 };
 
@@ -123,6 +124,7 @@ static void __attribute__((__noreturn__)) usage(void)
 
 	fputs(USAGE_OPTIONS, out);
 	fputs(_(" -q, --quiet        quiet mode - don't print anything\n"
+		"     --nofollow     do not follow symlink\n"
 		" -d, --fs-devno     print maj:min device number of the filesystem\n"
 		" -x, --devno        print maj:min device number of the block device\n"), out);
 	fputs(USAGE_SEPARATOR, out);
@@ -137,8 +139,13 @@ int main(int argc, char **argv)
 	int c;
 	struct mountpoint_control ctl = { NULL };
 
+	enum {
+		OPT_NOFOLLOW = CHAR_MAX + 1
+	};
+
 	static const struct option longopts[] = {
 		{ "quiet",    no_argument, NULL, 'q' },
+		{ "nofollow", no_argument, NULL, OPT_NOFOLLOW },
 		{ "fs-devno", no_argument, NULL, 'd' },
 		{ "devno",    no_argument, NULL, 'x' },
 		{ "help",     no_argument, NULL, 'h' },
@@ -159,6 +166,9 @@ int main(int argc, char **argv)
 		case 'q':
 			ctl.quiet = 1;
 			break;
+		case OPT_NOFOLLOW:
+			ctl.nofollow = 1;
+			break;
 		case 'd':
 			ctl.fs_devno = 1;
 			break;
@@ -179,17 +189,20 @@ int main(int argc, char **argv)
 		warnx(_("bad usage"));
 		errtryhelp(EXIT_FAILURE);
 	}
+	if (ctl.nofollow && ctl.dev_devno)
+		errx(EXIT_FAILURE, _("%s and %s are mutually exclusive"),
+		     "--devno", "--nofollow");
 
 	ctl.path = argv[optind];
-
-	if (stat(ctl.path, &ctl.st)) {
+	c = ctl.nofollow ? lstat(ctl.path, &ctl.st) : stat(ctl.path, &ctl.st);
+	if (c) {
 		if (!ctl.quiet)
 			err(EXIT_FAILURE, "%s", ctl.path);
 		return EXIT_FAILURE;
 	}
 	if (ctl.dev_devno)
 		return print_devno(&ctl) ? EXIT_FAILURE : EXIT_SUCCESS;
-	if (dir_to_device(&ctl)) {
+	if ((ctl.nofollow && S_ISLNK(ctl.st.st_mode)) || dir_to_device(&ctl)) {
 		if (!ctl.quiet)
 			printf(_("%s is not a mountpoint\n"), ctl.path);
 		return EXIT_FAILURE;

tests/expected/misc/mountpoint

@@ -0,0 +1,9 @@
+default
+./symlink-to-root is a mountpoint
+0
+try --nofollow
+./symlink-to-root is not a mountpoint
+1
+mutually exclusive
+mountpoint: --devno and --nofollow are mutually exclusive
+1

tests/ts/misc/mountpoint

@@ -0,0 +1,27 @@
+#!/bin/bash
+
+TS_TOPDIR="${0%/*}/../.."
+TS_DESC="mountpoint"
+
+. $TS_TOPDIR/functions.sh
+ts_init "$*"
+
+ts_check_test_command "$TS_CMD_MOUNTPOINT"
+
+ln -s / ./symlink-to-root
+
+echo "default" >> $TS_OUTPUT 2>&1
+$TS_CMD_MOUNTPOINT ./symlink-to-root >> $TS_OUTPUT 2>&1
+echo $? >> $TS_OUTPUT 2>&1
+
+echo "try --nofollow" >> $TS_OUTPUT 2>&1
+$TS_CMD_MOUNTPOINT --nofollow ./symlink-to-root >> $TS_OUTPUT 2>&1
+echo $? >> $TS_OUTPUT 2>&1
+
+echo "mutually exclusive" >> $TS_OUTPUT 2>&1
+$TS_CMD_MOUNTPOINT --devno --nofollow / >> $TS_OUTPUT 2>&1
+echo $? >> $TS_OUTPUT 2>&1
+
+rm -f ./symlink-to-root
+
+ts_finalize