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At the heart of fwupd is a plugin loader that gets run at startup, when devices get hotplugged and when updates are done. The idea is we have lots of small plugins that each do one thing, and are ordered by dependencies against each other at runtime. Using plugins we can add support for new hardware or new policies without making big changes all over the source tree.
There are broadly 3 types of plugin methods:
Mechanism: Upload binary data into a specific hardware device.
Policy: Control the system when updates are happening, e.g. preventing the user from powering-off.
Helpers: Providing more metadata about devices, for instance handling device quirks.
In general, building things out-of-tree isn't something that we think is
a very good idea; the API and ABI internal to fwupd is still
changing and there's a huge benefit to getting plugins upstream where
they can undergo review and be ported as the API adapts.
For this reason we don't install the plugin headers onto the system,
although you can of course just install the .so
binary file
manually.
A plugin only needs to define the vfuncs that are required, and the
plugin name is taken automatically from the suffix of the
.so
file.
Example 1. A sample plugin
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/* * Copyright (C) 2017 Richard Hughes */ #include <fu-plugin.h> #include <fu-plugin-vfuncs.h> struct FuPluginData { gpointer proxy; }; void fu_plugin_initialize (FuPlugin *plugin) { fu_plugin_add_rule (plugin, FU_PLUGIN_RULE_RUN_BEFORE, "dfu"); fu_plugin_alloc_data (plugin, sizeof (FuPluginData)); } void fu_plugin_destroy (FuPlugin *plugin) { FuPluginData *data = fu_plugin_get_data (plugin); destroy_proxy (data->proxy); } gboolean fu_plugin_startup (FuPlugin *plugin, GError **error) { FuPluginData *data = fu_plugin_get_data (plugin); data->proxy = create_proxy (); if (data->proxy == NULL) { g_set_error (error, FWUPD_ERROR, FWUPD_ERROR_NOT_SUPPORTED, "failed to create proxy"); return FALSE; } return TRUE; } |
We have to define when our plugin is run in reference to other plugins,
in this case, making sure we run before the dfu
plugin.
For most plugins it does not matter in what order they are run and
this information is not required.
This section shows how you would create a device which is exported
to the daemon and thus can be queried and updated by the client software.
The example here is all hardcoded, and a true plugin would have to
derive the details about the FuDevice
from the hardware,
for example reading data from sysfs
or /dev
.
Example 2. Example adding a custom device
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#include <fu-plugin.h> gboolean fu_plugin_coldplug (FuPlugin *plugin, GError **error) { g_autoptr(FuDevice) dev = NULL; fu_device_set_id (dev, "dummy-1:2:3"); fu_device_add_guid (dev, "2d47f29b-83a2-4f31-a2e8-63474f4d4c2e"); fu_device_set_version (dev, "1.2.3"); fu_device_get_version_lowest (dev, "1.2.2"); fu_device_get_version_bootloader (dev, "0.1.2"); fu_device_add_icon (dev, "computer"); fu_device_add_flag (dev, FWUPD_DEVICE_FLAG_UPDATABLE); fu_plugin_device_add (plugin, dev); return TRUE; } |
This shows a lot of the plugin architecture in action. Some notable points:
The device ID (dummy-1:2:3
) has to be unique on the
system between all plugins, so including the plugin name as a
prefix is probably a good idea.
The GUID value can be generated automatically using
fu_device_add_guid(dev,"some-identifier")
but is quoted
here explicitly.
The GUID value has to match the provides
value in the
.metainfo.xml
file for the firmware update to succeed.
Setting a display name and an icon is a good idea in case the GUI software needs to display the device to the user. Icons can be specified using a full path, although icon theme names should be preferred for most devices.
The FWUPD_DEVICE_FLAG_UPDATABLE
flag tells the client
code that the device is in a state where it can be updated.
If the device needs to be in a special mode (e.g. a bootloader) then
the FWUPD_DEVICE_FLAG_NEEDS_BOOTLOADER
flag can also be
used.
If the update should only be allowed when there is AC power available
to the computer (i.e. not on battery) then
FWUPD_DEVICE_FLAG_REQUIRE_AC
should be used as well.
There are other flags and the API documentation should be used when
choosing what flags to use for each kind of device.
Setting the lowest allows client software to refuse downgrading the device to specific versions. This is required in case the upgrade migrates some kind of data-store so as to be incompatible with previous versions. Similarly, setting the version of the bootloader (if known) allows the firmware to depend on a specific bootloader version, for instance allowing signed firmware to only be installable on hardware with a bootloader new enough to deploy it
Although it would be a wonderful world if we could update all hardware using a standard shared protocol this is not the universe we live in. Using a mechanism like DFU or UpdateCapsule means that fwupd will just work without requiring any special code, but for the real world we need to support vendor-specific update protocols with layers of backwards compatibility.
When a plugin has created a device that is FWUPD_DEVICE_FLAG_UPDATABLE
we can ask the daemon to update the device with a suitable
.cab
file.
When this is done the daemon checks the update for compatibility with
the device, and then calls the vfuncs to update the device.
Example 3. Updating a device
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gboolean fu_plugin_update (FuPlugin *plugin, FuDevice *dev, GBytes *blob_fw, FwupdInstallFlags flags, GError **error) { gsize sz = 0; guint8 *buf = g_bytes_get_data (blob_fw, &sz); /* write 'buf' of size 'sz' to the hardware */ return TRUE; } |
It's important to note that the blob_fw
is the binary
firmware file (e.g. .dfu
) and not
the .cab
binary data.
If FWUPD_INSTALL_FLAG_FORCE
is used then the usual checks
done by the flashing process can be relaxed (e.g. checking for quirks),
but please don't brick the users hardware even if they ask you to.
For some hardware, we might want to do an action before or after the actual firmware is squirted into the device. This could be something as simple as checking the system battery level is over a certain threshold, or it could be as complicated as ensuring a vendor-specific GPIO is asserted when specific types of hardware are updated.
Example 4. Running before a device update
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gboolean fu_plugin_update_prepare (FuPlugin *plugin, FuDevice *device, GError **error) { if (fu_device_has_flag (device, FWUPD_DEVICE_FLAG_REQUIRE_AC && !on_ac_power ()) { g_set_error_literal (error, FWUPD_ERROR, FWUPD_ERROR_AC_POWER_REQUIRED, "Cannot install update " "when not on AC power"); return FALSE; } return TRUE; } |
Example 5. Running after a device update
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gboolean fu_plugin_update_cleanup (FuPlugin *plugin, FuDevice *device, GError **error) { return g_file_set_contents ("/var/lib/fwupd/something", fu_device_get_id (device), -1, error); } |
Some hardware can only be updated in a special bootloader mode, which for most devices can be switched to automatically. In some cases the user to do something manually, for instance re-inserting the hardware with a secret button pressed.
Before the device update is performed the fwupd daemon runs an optional
update_detach()
vfunc which switches the device to
bootloader mode.
After the update (or if the update fails) an the daemon runs an
optional update_attach()
vfunc which should switch the
hardware back to runtime mode.
Finally an optional update_reload()
vfunc is run to
get the new firmware version from the hardware.
The optional vfuncs are only run on the plugin currently registered to handle the device ID, although the registered plugin can change during the attach and detach phases.
Example 6. Running before a device update
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gboolean fu_plugin_update_detach (FuPlugin *plugin, FuDevice *device, GError **error) { if (hardware_in_bootloader) return TRUE; return _device_detach(device, error); } |
Example 7. Running after a device update
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gboolean fu_plugin_update_attach (FuPlugin *plugin, FuDevice *device, GError **error) { if (!hardware_in_bootloader) return TRUE; return _device_attach(device, error); } |
Example 8. Running after a device update on success
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gboolean fu_plugin_update_reload (FuPlugin *plugin, FuDevice *device, GError **error) { g_autofree gchar *version = _get_version(plugin, device, error); if (version == NULL) return FALSE; fu_device_set_version(device, version); return TRUE; } |
The fwupd daemon provides a per-plugin cache which allows objects
to be added, removed and queried using a specified key.
Objects added to the cache must be GObject
s to enable the
cache objects to be properly refcounted.
If the fwupd daemon is started with --plugin-verbose=$plugin
then the environment variable FWUPD_$PLUGIN_VERBOSE
is
set process-wide.
This allows plugins to detect when they should output detailed debugging
information that would normally be too verbose to keep in the journal.
For example, using --plugin-verbose=unifying
would set
FWUPD_UNIFYING_VERBOSE=1
.