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

Srinivas, Vidya
2026-04-07T13:47:22Z

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From: Purkait, Soham <soham.purkait@intel.com>
Sent: 06 April 2026 22:05
To: Srinivas, Vidya <vidya.srinivas@intel.com>; igt-dev@lists.freedesktop.org; Konieczny, Kamil <kamil.konieczny@intel.com>
Subject: Re: tools/gputop: Fix zero output when stdout is not a terminal

Hi Vidya,
On 06-04-2026 11:11, Srinivas, Vidya wrote:

-----Original Message-----

From: Purkait, Soham <soham.purkait@intel.com><mailto:soham.purkait@intel.com>

Sent: 06 April 2026 10:27

To: Srinivas, Vidya <vidya.srinivas@intel.com><mailto:vidya.srinivas@intel.com>; igt-dev@lists.freedesktop.org<mailto:igt-dev@lists.freedesktop.org>;

Konieczny, Kamil <kamil.konieczny@intel.com><mailto:kamil.konieczny@intel.com>

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

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.

Hello,

Many thanks for the review.

I will update the patch like this. Should be okay?

if (ioctl(STDOUT_FILENO, TIOCGWINSZ, &ws) == -1 &&

ioctl(STDIN_FILENO, TIOCGWINSZ, &ws) == -1 &&

ioctl(STDERR_FILENO, TIOCGWINSZ, &ws) == -1) {

I assume it's better to keep this : "if (ioctl(0, TIOCGWINSZ, &ws) == -1)" as is. As it won't make any issue if the gputop output is redirected to any file or so (which only involve stdout). The expression will only be true when stdin is not a terminal, may be during running gputop in a ci.
And Its better to assign the default values to con_w and con_h in main. (please see below)

Hello Soham

Apologies for missing your point. Thank you for the pointers and review.

Have pushed v3 with your suggestion

https://patchwork.freedesktop.org/series/164301/#rev3

Please have a check.

Regards

Vidya

ws.ws_col = 80;

ws.ws_row = 50;

}

Regards

Vidya

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><mailto:vidya.srinivas@intel.com>

Reviewed-by: Kamil Konieczny <kamil.konieczny@linux.intel.com><mailto: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;

Imho instead of setting the values (*w = 80;*h = 50) here , it's better to initialize these as default values in main as "int con_w = 80, con_h = 50;"

Thanks, Soham

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;

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