Question about xorg.conf.d's searching path

[Dan Nicholson]

On Tue, Mar 27, 2012 at 2:38 AM, Zhigang Gong
<zhigang.gong at linux.intel.com> wrote:
> Hi,
>
>
>
> I’m building xorg in a local directory $HOME/xorg, then all libraries will
> go to $HOME/xorg/lib,
>
> And all the configure files will go to $HOME/xorg/share/X11/xorg.conf.d/,
> such as the 10-evdev.conf.
>
>
>
> My question is, when I run this local Xorg it will not search the configure
> file at the local configure directory:
>
> $HOME/xorg/share/X11/xorg.conf.d/
>
> Instead, it searches the system’s xorg configuration file at:
>
> /etc/X11/xorg.conf.d
>
> /usr/share/X11/xorg.conf.d
>
>
>
> So you can see, when I run the new Xserver, it will load the old
> configuration files rather than the correct files
>
> Installed at local configuration directory.
>
>
>
> I traced into the source code, and found the reason is as below:
>
>
>
> the macro SYS_CONFIGDIRPATH’s defined as "/usr/share/X11/%X," "%D/X11/%X",
>
> And it will be used to find the system config path. And the finding process
> is at function OpenConfigDir(), the finding mechanism
>
> is to scan the SYS_CONFIGDIRPATH from left to right, and if it successfully
> find a directory, then it stop finding next. As my system has
>
> a /usr/share/X11/xorg.conf.d, it stop to find the next path which is
> pointing to my local directory and which is the one should be
>
> used here IMHO. As all the building process in my local building repository
> will install configuration files into local files rather than
>
> the /usr/share/X11/xorg.conf.d.
>
>
>
> I know there may be many duplicate config files in these two directories, so
> we have to pick one and discard the other one. In my
>
> opinion, the local directory should be higher priority. Otherwise, how can
> we ensure we use the correct file when we build a new
>
> xserver which has difference config files？
>
>
>
> Any suggestion?

I had to remind myself how this works, but I think I get it looking
through the code again.

I believe the idea is that since the xserver is running with high
privileges and making non-trivial access to hardware that the
configuration specified by the vendor/administrator takes precedence.
Looking through the oddball code in hw/xfree86/common/xf86Config.c and
hw/xfree86/parser/scan.c, the code will look under $sysconfdir and
$datadir if the equivalent directories are not found under /etc/X11 or
/usr/share/X11, respectively.

You can define some macros during the build if you want to change the
order a bit.

export CPPFLAGS="-DSYS_CONFIGDIRPATH=\"%D/X11/%X,/usr/share/X11/%X\""

That would reverse the order from the default since %D expands to
$datadir. Arguably this should be available as a configure option, but
no one did that work and I worry that trying to expose the % tokens
would be difficult to explain.

--
Dan