[PATCH] tools/gputop: Fix zero output when stdout is not a terminal

Vidya Srinivas
2026-04-02T13:50:30Z

When gputop output is redirected to a file or pipe, such as:

gputop -n 5 -d 1 > results.txt
gputop -n 3 -d 2 | grep rcs

ioctl(0, TIOCGWINSZ) fails with -1 since stdin is not a terminal.
update_console_size() then returns without setting *w and *h, leaving
con_w and con_h at their initial value of -1.

The main display loop uses 'if (lines >= con_h) break' to limit output
to the terminal height. With con_h = -1, the condition (0 >= -1) is
immediately true on the very first line, causing all client output to be
silently suppressed. The result is that gputop produces only ANSI clear-
screen escape sequences and zero actual data.

This affects anyone using gputop in automation, CI pipelines, or any
non-interactive context on Linux or Android where output is redirected
or piped.

Fix this by falling back to a default console size of 80x50 when the
ioctl fails, consistent with the existing fallback for serial consoles
(where ws_col and ws_row are both 0).

Signed-off-by: Vidya Srinivas <vidya.srinivas@intel.com>
---
tools/gputop.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/tools/gputop.c b/tools/gputop.c
index 9b2e8cb6f..112ec5ddb 100644
--- a/tools/gputop.c
+++ b/tools/gputop.c
@@ -505,8 +505,11 @@ static void update_console_size(int *w, int *h)
{
struct winsize ws = {};

- if (ioctl(0, TIOCGWINSZ, &ws) == -1)
+ if (ioctl(0, TIOCGWINSZ, &ws) == -1) {
+ *w = 80;
+ *h = 50;
return;
+ }

*w = ws.ws_col;
*h = ws.ws_row;
--
2.45.2