As per Bug 735974, gnome-desktop is using only one function, gs_file_read_noatime(), from libgsystem. Is it even worth copying it (it is quite a large function once you unroll it) just to avoid updating access times? (or is there another advantage to using that function?)

I'd just copy the one file that we use from libgsystem, and add an "update-from-libgsystem.sh" helper, as we do in other cut'n'paste situations:
https://git.gnome.org/browse/gnome-control-center/tree/panels/wacom/Makefile.am#n81

Created attachment 296234 [details] [review]
Drop libgsystem submodule, stop using O_NOATIME

The entire rationale for adding this _noatime function was fairly
bogus.

See https://bugzilla.gnome.org/show_bug.cgi?id=680326

But the Linux kernel doesn't permit non-root users to use it for
root-owned files - which is the default for real world GNOME
installations.  We end up doing twice the syscall traffic with no
benefit at all.

The patch does work in jhbuild, but honestly the relatime handling is
generally OK for this, and where it's not, change your system to mount
O_NOATIME.

I want to have libgsystem potentially become more Linux specific, and having gnome-desktop depend on it is problematic from that perspective.

Review of attachment 296234 [details] [review]:

Rest looks fine.

::: libgnome-desktop/gnome-desktop-thumbnail.c
@@ -495,1 @@
             input_stream = G_INPUT_STREAM (g_file_read (file, NULL, &error));

You'll need to unmangle the indentation of that line.

Attachment 296234 [details] pushed as c394ae4 - Drop libgsystem submodule, stop using O_NOATIME