perf ui browser: Allow specifying message to show when no samples are available to display

The 'perf top' tool will use that to avoid having a initial blank screen
while collecting the minimum number of samples to sort and display.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lkml.kernel.org/n/tip-89ciceg8cy4442he3t0jzo3f@git.kernel.orgSigned-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/ui/browser.c

@@ -347,6 +347,8 @@ static int __ui_browser__refresh(struct ui_browser *browser)
 	SLsmg_fill_region(browser->y + row + browser->extra_title_lines, browser->x,
 			  browser->rows - row, width, ' ');
 
+	if (browser->nr_entries == 0 && browser->no_samples_msg)
+		__ui__info_window(NULL, browser->no_samples_msg, NULL);
 	return 0;
 }
 

tools/perf/ui/browser.h

@@ -23,6 +23,7 @@ struct ui_browser {
 	void	      *priv;
 	const char    *title;
 	char	      *helpline;
+	const char    *no_samples_msg;
 	void 	      (*refresh_dimensions)(struct ui_browser *browser);
 	unsigned int  (*refresh)(struct ui_browser *browser);
 	void	      (*write)(struct ui_browser *browser, void *entry, int row);