Give access to removable devices and other temporary mounts

Currently, when udisks is configured to use /run/media instead of
/media, on most operating systems, the /run/media directory is created
by udisks itself when the first mount is handled [1]. This causes
problems when creating the toolbox container, if nothing has been
mounted after the current boot, because a missing directory cannot be
bind mounted.

Fedora Silverblue is a significant exception to the above, where
rpm-ostree takes care of creating /run/media with systemd-tmpfiles [2]
during boot.

The correct long-term solution is to get udisks to create /run/media
during boot with systemd-tmpfiles by installing a snippet in
tmpfiles.d [3, 4]. Until that happens, and is widely deployed, the
toolbox needs to provide the snippet itself to make things work on
the majority of operating systems.

Note that, in case udisks is configured to use /media instead of
/run/media, then this will create an unused /run/media directory. This
is probably fine because /run/media is the default setting for udisks.
Moreover, an unused directory is way better than not being able to
access mount points from a toolbox container or having 'podman create'
fail due to a missing directory.

Based on 4a2a15f and as suggested by
Daniel J Walsh.

[1] UDisks commit aa02e5fc53efdeaf
    storaged-project/udisks@aa02e5fc53efdeaf
[2] rpm-ostree commit 958dfa435e4e4a3e
    coreos/rpm-ostree@958dfa435e4e4a3e
[3] https://www.freedesktop.org/software/systemd/man/tmpfiles.d.html
[4] storaged-project/udisks#641

https://github.com/debarshiray/toolbox/issues/3

data/meson.build

@@ -0,0 +1 @@
+subdir('tmpfiles.d')

data/tmpfiles.d/meson.build

@@ -0,0 +1,4 @@
+install_data(
+  'toolbox.conf',
+  install_dir: tmpfilesdir,
+)

data/tmpfiles.d/toolbox.conf

@@ -0,0 +1 @@
+d /run/media 0755 root root

meson.build

@@ -7,9 +7,13 @@ project(
 
 go_md2man = find_program('go-md2man')
 
+systemd_dep = dependency('systemd')
+tmpfilesdir = systemd_dep.get_pkgconfig_variable('tmpfilesdir')
+
 install_data(
   'toolbox',
   install_dir: get_option('bindir'),
 )
 
+subdir('data')
 subdir('doc')

toolbox

@@ -595,6 +595,9 @@ create()
             --volume "$dbus_system_bus_path":"$dbus_system_bus_path" \
             --volume /dev/dri:/dev/dri \
             --volume /dev/fuse:/dev/fuse \
+            --volume /media:/media:rslave \
+            --volume /mnt:/mnt:rslave \
+            --volume /run/media:/run/media:rslave \
             $toolbox_image \
             /bin/sh >/dev/null 2>&3
     ret_val=$?