stat: fix use of devname(3)

Besides being a little hard to parse through visually, this had its own
bug of inspecting st->st_mode to determine what to pass to devname(3),
which is only correct for st_rdev.

For st_dev, you're likely to be looking at files or directories and
attempting to assess what device they're located on, so the mode is
meaningless- we just have to assume that our filesystems are on
character devices and attempt to resolve st_dev as such.

Reviewed by:	des, kib (previous version)
Differential Revision:	https://reviews.freebsd.org/D56565

usr.bin/stat/stat.c

@@ -650,6 +650,7 @@ format1(const struct stat *st,
 	struct timespec ts;
 	struct tm *tm;
 	int l, small, formats;
+	mode_t dtype;
 
 	tsp = NULL;
 	formats = 0;
@@ -665,9 +666,16 @@ format1(const struct stat *st,
 		small = (sizeof(st->st_dev) == 4);
 		data = (what == SHOW_st_dev) ? st->st_dev : st->st_rdev;
 #if HAVE_DEVNAME
-		sdata = devname(what == SHOW_st_dev ? st->st_dev :
-		    st->st_rdev, S_ISCHR(st->st_mode) ? S_IFCHR :
-		    (S_ISBLK(st->st_mode) ? S_IFBLK : 0));
+		switch (what) {
+		case SHOW_st_dev:
+			dtype = S_IFCHR;
+			break;
+		case SHOW_st_rdev:
+			dtype = st->st_mode & (S_IFCHR | S_IFBLK);
+			break;
+		}
+
+		sdata = devname(data, dtype);
 #endif /* HAVE_DEVNAME */
 		if (hilo == HIGH_PIECE) {
 			data = major(data);

usr.bin/stat/tests/stat_test.sh

@@ -25,6 +25,8 @@
 # SUCH DAMAGE.
 #
 
+: ${CHKPATH:="mnt"}
+
 atf_test_case F_flag
 F_flag_head()
 {
@@ -301,6 +303,36 @@ x_flag_body()
 	done
 }
 
+atf_test_case devname cleanup
+devname_head()
+{
+	atf_set	"descr" "Verify that %Sd outputs a device name"
+}
+devname_body()
+{
+	local devname devpath
+
+	atf_check -o save:dev mdconfig -t malloc -s 16M
+	read devname < dev
+	devpath="/dev/$devname"
+	atf_check -o not-empty newfs "$devpath"
+
+	atf_check mkdir "$CHKPATH"
+	atf_check mount "$devpath" "$CHKPATH"
+
+	atf_check -o inline:"$devname\n" stat -f '%Sd' "$CHKPATH"
+	atf_check -o inline:"$devname\n" stat -f '%Sr' "$devpath"
+}
+devname_cleanup()
+{
+	if [ -d "$CHKPATH" ]; then
+		umount "$CHKPATH" || true
+	fi
+	if [ -f dev ]; then
+		mdconfig -d -u $(cat dev) || true
+	fi
+}
+
 atf_init_test_cases()
 {
 	atf_add_test_case F_flag
@@ -315,4 +347,5 @@ atf_init_test_cases()
 	atf_add_test_case s_flag
 	atf_add_test_case t_flag
 	atf_add_test_case x_flag
+	atf_add_test_case devname
 }