du: Print progress information to stderr

* On SIGINFO, print the current path to stderr rather than stdout.

* Do so immediately, instead of the next time we finish a directory.

* Document this behavior in the manual page.

PR:		296861
MFC after:	1 week
Fixes:          d1588599c0 ("Report the next directory being scanned ...")
Reviewed by:	wollman
Differential Revision:	https://reviews.freebsd.org/D58702

usr.bin/du/du.1

@@ -25,7 +25,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd June 9, 2026
+.Dd August 7, 2026
 .Dt DU 1
 .Os
 .Sh NAME
@@ -195,6 +195,16 @@ and
 .Fl Fl si
 options all override each other; the last one specified determines
 the block counts used.
+.Pp
+If
+.Nm
+receives a
+.Dv SIGINFO
+(see the
+.Cm status
+argument for
+.Xr stty 1 )
+signal, the current file will be written to the standard error output.
 .Sh ENVIRONMENT
 .Bl -tag -width BLOCKSIZE
 .It Ev BLOCKSIZE

usr.bin/du/du.c

@@ -270,6 +270,10 @@ main(int argc, char *argv[])
 	xo_open_container("disk-usage-information");
 	xo_open_list("paths");
 	for (errno = 0; (p = fts_read(fts)) != NULL; errno = 0) {
+		if (info) {
+			info = 0;
+			(void)fprintf(stderr, "\t%s\n", p->fts_path);
+		}
 		switch (p->fts_info) {
 		case FTS_D:			/* Ignore. */
 			if (ignorep(p))
@@ -284,10 +288,6 @@ main(int argc, char *argv[])
 			if (p->fts_level <= depth && check_threshold(p))
 				print_file_size(p);
 
-			if (info) {
-				info = 0;
-				(void)printf("\t%s\n", p->fts_path);
-			}
 			break;
 		case FTS_DC:			/* Ignore. */
 			break;