• Thomas Haller's avatar
    settings: rework tracking settings connections and settings plugins · d35d3c46
    Thomas Haller authored
    Completely rework how settings plugin handle connections and how
    NMSettings tracks the list of connections.
    
    Previously, settings plugins would return objects of (a subtype of) type
    NMSettingsConnection. The NMSettingsConnection was tightly coupled with
    the settings plugin. That has a lot of downsides.
    
    Change that. When changing this basic relation how settings connections
    are tracked, everything falls appart. That's why this is a huge change.
    Also, since I have to largely rewrite the settings plugins, I also
    added support for multiple keyfile directories, handle in-memory
    connections only by keyfile plugin and (partly) use copy-on-write NMConnection
    instances. I don't want to spend effort rewriting large parts while
    preserving the old way, that anyway should change. E.g. while rewriting ifcfg-rh,
    I don't want to let it handle in-memory connections because that's not right
    long-term.
    
    --
    
    If the settings plugins themself create subtypes of NMSettingsConnection
    instances, then a lot of knowledge about tracking connections moves
    to the plugins.
    Just try to follow the code what happend during nm_settings_add_connection().
    Note how the logic is spread out:
     - nm_settings_add_connection() calls plugin's add_connection()
     - add_connection() creates a NMSettingsConnection subtype
     - the plugin has to know that it's called during add-connection and
       not emit NM_SETTINGS_PLUGIN_CONNECTION_ADDED signal
     - NMSettings calls claim_connection() which hocks up the new
       NMSettingsConnection instance and configures the instance
       (like calling nm_settings_connection_added()).
    This summary does not sound like a lot, but try to follow that code. The logic
    is all over the place.
    
    Instead, settings plugins should have a very simple API for adding, modifying,
    deleting, loading and reloading connections. All the plugin does is to return a
    NMSettingsStorage handle. The storage instance is a handle to identify a profile
    in storage (e.g. a particular file). The settings plugin is free to subtype
    NMSettingsStorage, but it's not necessary.
    There are no more events raised, and the settings plugin implements the small
    API in a straightforward manner.
    NMSettings now drives all of this. Even NMSettingsConnection has now
    very little concern about how it's tracked and delegates only to NMSettings.
    
    This should make settings plugins simpler. Currently settings plugins
    are so cumbersome to implement, that we avoid having them. It should not be
    like that and it should be easy, beneficial and lightweight to create a new
    settings plugin.
    
    Note also how the settings plugins no longer care about duplicate UUIDs.
    Duplicated UUIDs are a fact of life and NMSettings must handle them. No
    need to overly concern settings plugins with that.
    
    --
    
    NMSettingsConnection is exposed directly on D-Bus (being a subtype of
    NMDBusObject) but it was also a GObject type provided by the settings
    plugin. Hence, it was not possible to migrate a profile from one plugin to
    another.
    However that would be useful when one profile does not support a
    connection type (like ifcfg-rh not supporting VPN). Currently such
    migration is not implemented except for migrating them to/from keyfile's
    run directory. The problem is that migrating profiles in general is
    complicated but in some cases it is important to do.
    
    For example checkpoint rollback should recreate the profile in the right
    settings plugin, not just add it to persistent storage. This is not yet
    properly implemented.
    
    --
    
    Previously, both keyfile and ifcfg-rh plugin implemented in-memory (unsaved)
    profiles, while ifupdown plugin cannot handle them. That meant duplication of code
    and a ifupdown profile could not be modified or made unsaved.
    This is now unified and only keyfile plugin handles in-memory profiles (bgo #744711).
    Also, NMSettings is aware of such profiles and treats them specially.
    In particular, NMSettings drives the migration between persistent and non-persistent
    storage.
    
    Note that a settings plugins may create truly generated, in-memory profiles.
    The settings plugin is free to generate and persist the profiles in any way it
    wishes. But the concept of "unsaved" profiles is now something explicitly handled
    by keyfile plugin. Also, these "unsaved" keyfile profiles are persisted to file system
    too, to the /run directory. This is great for two reasons: first of all, all
    profiles from keyfile storage in fact have a backing file -- even the
    unsaved ones. It also means you can create "unsaved" profiles in /run
    and load them with `nmcli connection load`, meaning there is a file
    based API for creating unsaved profiles.
    The other advantage is that these profiles now survive restarting
    NetworkManager. It's paramount that restarting the daemon is as
    non-disruptive as possible. Persisting unsaved files to /run improves
    here significantly.
    
    --
    
    In the past, NMSettingsConnection also implemented NMConnection interface.
    That was already changed a while ago and instead users call now
    nm_settings_connection_get_connection() to delegate to a
    NMSimpleConnection. What however still happened was that the NMConnection
    instance gets never swapped but instead the instance was modified with
    nm_connection_replace_settings_from_connection(), clear-secrets, etc.
    Change that and treat the NMConnection instance immutable. Instead of modifying
    it, reference/clone a new instance. This changes that previously when somebody
    wanted to keep a reference to an NMConnection, then the profile would be cloned.
    Now, it is supposed to be safe to reference the instance directly and everybody
    must ensure not to modify the instance. nmtst_connection_assert_unchanging()
    should help with that.
    The point is that the settings plugins may keep references to the
    NMConnection instance, and so does the NMSettingsConnection. We want
    to avoid cloning the instances as long as they are the same.
    Likewise, the device's applied connection can now also be referenced
    instead of cloning it. This is not yet done, and possibly there are
    further improvements possible.
    
    --
    
    Also implement multiple keyfile directores /usr/lib, /etc, /run (rh #1674545,
    bgo #772414).
    
    It was always the case that multiple files could provide the same UUID
    (both in case of keyfile and ifcfg-rh). For keyfile plugin, if a profile in
    read-only storage in /usr/lib gets modified, then it gets actually stored in
    /etc (or /run, if the profile is unsaved).
    
    --
    
    While at it, make /etc/network/interfaces profiles for ifupdown plugin reloadable.
    
    --
    
    https://bugzilla.gnome.org/show_bug.cgi?id=772414
    https://bugzilla.gnome.org/show_bug.cgi?id=744711
    https://bugzilla.redhat.com/show_bug.cgi?id=1674545
    d35d3c46
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debug-helper.py Loading commit data...
enums-to-docbook.pl Loading commit data...
meson-post-install.sh Loading commit data...
run-nm-test.sh Loading commit data...
test-build.sh Loading commit data...
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