Re: tools/gputop: Fix zero output when stdout is not a terminal

Purkait, Soham
2026-04-06T04:57:06Z

Hi Vidya,

On 02-04-2026 19:15, Vidya Srinivas wrote:
> When gputop output is redirected to a file or pipe, such as:
>
> gputop -n 5 -d 1 > results.txt

Isn’t only stdout (fd 1) redirected to the file here?

I guess some thing like "echo test | ./gputop" would be returning the
default value (-1 in this case) for con_h.

> 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>
> Reviewed-by: Kamil Konieczny <kamil.konieczny@linux.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;
How about assigning the values during initialization in the main function ?

eg : int con_w = 80, con_h = 50;

Thanks,
Soham

> return;
> + }
>
> *w = ws.ws_col;
> *h = ws.ws_row;