The software is licensed under GPL-2.0-or-later

The software is licensed under GPL-2.0-or-later. But list.c and list.h
contain source code I edited from book "C Primer Plus" Chapter17
practice problem 2 which contain codes from its example codes, and the
author of "C Primer Plus" does not have a license for list.c and list.h,
so the author of "C Primer Plus" has the copyright on list.c and list.h,
so list.c and list.h can be considered non-free close souce proprietary
code.

I choose GPL-2.0-or-later. Because I prefer GPL over LGPL. And because
libssh's LGPL-2.1-or-later, plplot's LGPL-2.0-or-later, and gtk's
LGPL-2.1-or-later licenses are compatible with GPL-2.0-or-later.

This commit also clarify licensing by copy the GPL-2.0-or-later license
to LICENSE file, adding notes in README.md, and adding
SPDX-License-Identifier and other licensing comment in source code
files.

1 files changed, 8 insertions, 3 deletions

diff --git a/remote_plot.c b/remote_plot.c
index ba3cec4..5f7650d 100644
--- a/remote_plot.c
+++ b/remote_plot.c
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
 // references:
 // https://api.libssh.org/stable/libssh_tutorial.html
 // https://api.libssh.org/stable/libssh_tutor_guided_tour.html
@@ -9,10 +11,12 @@
 // https://gitlab.gnome.org/GNOME/gtk/-/blob/main/demos/print-editor/print-editor.c
 // https://gitlab.gnome.org/GNOME/gtk/-/blob/main/demos/gtk-demo/main.c
 
+// libssh, license LGPL-2.1-or-later
 #include <libssh/libssh.h>
+#include <libssh/sftp.h>
+
 #include <stdlib.h>
 #include <stdio.h>
-#include <libssh/sftp.h>
 
 // verify_knownhost()
 #include <errno.h>
@@ -20,14 +24,15 @@
 
 #include <fcntl.h> // open()
 
-// plplot
+// plplot, license GPL-2.0-or-later
 #include <plplot/plConfig.h>
 #include <plplot/plplot.h>
+
 #include <math.h>
 //#include <stdlib.h>
 #include <time.h>
 #include <unistd.h>
-#include <gtk/gtk.h>
+#include <gtk/gtk.h> // license LGPL-2.1-or-later
 
 // Using a linked list to hold all the voltages and temperatures data
 #include "list.h"