$ find * -type f |xargs perl contrib/scripts/spdx.pl
  $ git rm contrib/scripts/spdx.pl

We no longer add these. If you use Emacs, configure it yourself.

Also, due to our "smart-tab" usage the editor anyway does a subpar
job handling our tabs. However, on the upside every user can choose
whatever tab-width he/she prefers. If "smart-tabs" are used properly
(like we do), every tab-width will work.

No manual changes, just ran commands:

    F=($(git grep -l -e '-\*-'))
    sed '1 { /\/\* *-\*-  *[mM]ode.*\*\/$/d }'     -i "${F[@]}"
    sed '1,4 { /^\(#\|--\|dnl\) *-\*- [mM]ode/d }' -i "${F[@]}"

Check remaining lines with:

    git grep -e '-\*-'

The ultimate purpose of this is to cleanup our files and eventually use
SPDX license identifiers. For that, first get rid of the boilerplate lines.

During shutdown, we will need to still iterate the main loop
to do a coordinated shutdown. Currently we do not, and we just
exit, leaving a lot of objects hanging.

If we are going to fix that, we need during shutdown tell
NMDBusManager to reject all future operations.

Note that property getters and "GetManagerObjects" call is not
blocked. It continues to work.

Certainly for some operations, we want to allow them to be called even
during shutdown. However, these have to opt-in.

This also fixes an uglyness, where nm_dbus_manager_start() would
get the set-property-handler and the @manager as user-data. However,
NMDBusManager will always outlife NMManager, hence, after NMManager
is destroyed, the user-data would be a dangling pointer. Currently
that is not an issue, because
  - we always leak NMManager
  - we don't run the mainloop during shutdown

When one D-Bus object exposes (the path of) another D-Bus object,
we want that the path property gets cleared before the other
object gets unexported(). That essentially requires to register
to the "exported-changed" signal.

Add a helper struct NMDBusTrackObjPath to help with this.

The GObject property "path" exists for the sole reasons so that
other components can connect to the "notify::path" signal.

However, notifications are blocked by g_object_freeze_notify(),
and especially for NMDBusObject we want to make use of that to
combine multiple PropertiesChanged events into one.

This blocking of the signal is not desired for the case where
we wait for "notify::path". Convert that to a signal, which
will not be blocked.

GVariant is immutable and can nicely be shared and cached.
Cache the property variants. This makes getting the properties
faster, at the expense of using some extra memory.

Tested with https://tratt.net/laurie/src/multitime/

  $ multitime -n 200 -s 0 bash -c 'echo -n .; exec busctl call org.freedesktop.NetworkManager /org/freedesktop org.freedesktop.DBus.ObjectManager GetManagedObjects &>/dev/null'
  #                     Mean                Std.Dev.    Min         Median      Max
  # real(before)        0.013+/-0.0000      0.001       0.012       0.013       0.019
  # real(after)         0.013+/-0.0000      0.002       0.011       0.012       0.034

  $ multitime -n 100 -s 0 bash -c 'for i in {1..5}; do busctl call org.freedesktop.NetworkManager /org/freedesktop org.freedesktop.DBus.ObjectManager GetManagedObjects &>/dev/null & done; wait; echo -n .'
  #                     Mean                Std.Dev.    Min         Median      Max
  # real(before)        0.040+/-0.0000      0.002       0.037       0.040       0.049
  # real(after)         0.037+/-0.0000      0.002       0.034       0.036       0.045

  $ multitime -n 30 -s 0 bash -c 'for i in {1..100}; do busctl call org.freedesktop.NetworkManager /org/freedesktop org.freedesktop.DBus.ObjectManager GetManagedObjects &>/dev/null & done; wait; echo -n .'
  #                     Mean                Std.Dev.    Min         Median      Max
  # real(before)        0.704+/-0.0000      0.016       0.687       0.701       0.766
  # real(after)         0.639+/-0.0000      0.013       0.622       0.637       0.687

  $ multitime -n 200 -s 0 bash -c 'echo -n .; exec nmcli &>/dev/null'
  #                     Mean                Std.Dev.    Min         Median      Max
  # real(before)        0.092+/-0.0000      0.005       0.081       0.092       0.119
  # real(after)         0.092+/-0.0000      0.005       0.080       0.091       0.123

  $ multitime -n 100 -s 0 bash -c 'for i in {1..5}; do nmcli &>/dev/null & done; wait; echo -n .'
  #                     Mean                Std.Dev.    Min         Median      Max
  # real(before)        0.436+/-0.0000      0.043       0.375       0.424       0.600
  # real(after)         0.413+/-0.0000      0.022       0.380       0.410       0.558

  $ multitime -n 20 -s 0 bash -c 'for i in {1..100}; do nmcli &>/dev/null & done; wait; echo -n .'
  #                     Mean                Std.Dev.    Min         Median      Max
  # real(before)        8.796+/-0.1070      0.291       8.073       8.818       9.247
  # real(after)         8.736+/-0.0893      0.243       8.017       8.780       9.101

The time savings are small, but that is because caching mostly speeds up
the GetManagedObjects calls, and that is only a small part of the entire
nmcli call from client side.

I dislike the static hash table to cache the integer counter for
numbered paths. Let's instead cache the counter at the class instance
itself -- since the class contains the information how the export
path should be exported.

However, we cannot use a plain integer field inside the class structure,
because the class is copied between derived classes. For example,
NMDeviceEthernet and NMDeviceBridge both get a copy of the NMDeviceClass
instance. Hence, the class doesn't contain the counter directly, but
a pointer to one counter that can be shared between sibling classes.