path: root/docs/reference/api/ModemManager-overview.xml

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<part id="ref-overview">
  <title>ModemManager Overview</title>

  <chapter id="ref-overview-introduction">
    <title>Introduction</title>
    <para>
      ModemManager provides a unified high level API for communicating with mobile
      broadband modems, regardless of the protocol used to communicate with the
      actual device (Generic AT, vendor-specific AT, QCDM, QMI, MBIM...).
    </para>
    <formalpara>
      <title>Using</title>
      <para>
        ModemManager is a system daemon and is not meant to be used directly from
        the command line. However, since it provides a DBus API, it is possible to use
        'dbus-send' commands or the new 'mmcli' command line interface to control it
        from the terminal. The devices are queried from udev and automatically updated
        based on hardware events, although a manual re-scan can also be requested to
        look for RS232 modems.
      </para>
    </formalpara>
    <formalpara>
      <title>Implementation</title>
      <para>
        ModemManager is a DBus system bus activated service (meaning it's started
        automatically when a request arrives). It is written in C, using glib and gio.
        Several GInterfaces specify different features that the modems support,
        including the generic MMIfaceModem3gpp and MMIfaceModemCdma which provice basic
        operations for 3GPP (GSM, UMTS, LTE) or CDMA (CDMA1x, EV-DO) modems. If a given
        feature is not available in the modem, the specific interface will not be
        exported in DBus.
      </para>
    </formalpara>
    <formalpara>
      <title>Plugins</title>
      <para>
        Plugins are loaded on startup, and must implement the MMPlugin interface. It
        consists of a couple of methods which tell the daemon whether the plugin
        supports a port and to create custom MMBroadbandModem implementations. It most
        likely makes sense to derive custom modem implementations from one of the
        generic classes and just add (or override) operations which are not standard.
        There are multiple fully working plugins in the plugins/ directory that can be
        used as an example for writing new plugins. Writing new plugins is highly
        encouraged! The plugin API is open for changes, so if you're writing a plugin
        and need to add or change some public method, feel free to suggest it!
      </para>
    </formalpara>
  </chapter>

  <chapter id="ref-overview-modem-detection">
    <title>Modem detection</title>

    <section>
      <title>Builds with udev support</title>
      <para>
        ModemManager requires <emphasis>udev</emphasis>-powered Linux kernels in order
        to get notified of possible available Modems. udev will report each of the ports
        found in the device, and ModemManager will consider for probing each of the ports
        marked with the <emphasis>ID_MM_CANDIDATE</emphasis> tag in udev.
      </para>
      <para>
        Aditionally, users of RS232-based devices may need to request additional manual
        scans via DBus, in order to detect modems that may have been connected to
        RS232 to USB adapters. In this case, udev just knows about the USB adapter being
        connected, not about the RS232 modem connected to the adapter, if any.
      </para>
    </section>

    <section>
      <title>Builds without udev support</title>
      <para>
        When the udev daemon isn't available in the system, the
        <link linkend="gdbus-method-org-freedesktop-ModemManager1.ReportKernelEvent">ReportKernelEvent</link>
        method in the
        <link linkend="gdbus-org.freedesktop.ModemManager1">Manager interface</link>
        may be used to notify the ModemManager daemons of device addition and removals.
      </para>
      <para>
        When udev support is disabled in the build, the <emphasis>ID_MM_CANDIDATE</emphasis>
        tag and manual scan requests are still applicable. ModemManager has a built-in parser
        of udev rule files that is enabled when udev itself isn't available.
      </para>
    </section>
  </chapter>

  <chapter id="ref-overview-modem-filter">
    <title>Modem filter</title>

    <para>
      ModemManager will not probe all TTYs, NET and cdc-wdm ports found in the system,
      as this may end up interfering e.g. with TTYs that have nothing to do with modem
      devices.
    </para>
    <para>
      The daemon comes with several predefined <emphasis>filter policies</emphasis>, each
      of them composed of one or more <emphasis>filter rules</emphasis>.
    </para>

    <section>
      <title>Filter rules</title>
      <para>
        The device filter in ModemManager defines the following independent filter rules. The
        predefined filter policies are based on one or more of these predefined filter rules.
        <itemizedlist>
          <listitem>
            <para><emphasis>MM_FILTER_RULE_EXPLICIT_WHITELIST</emphasis></para>
            <para>
              This filter allows users to manually tag devices and/or device ports with the
              <emphasis>ID_MM_DEVICE_PROCESS</emphasis> udev tag. If the filter finds this tag,
              the device and/or device ports will be automatically accepted and port probing
              will be allowed.
            </para>
            <programlisting>
$ sudo vim /lib/udev/rules.d/78-mm-whitelist-internal-modem.rules
    ACTION!="add|change|move", GOTO="mm_whitelist_internal_modem_end"
    ATTRS{idVendor}=="1199", ATTRS{idProduct}=="a001", ENV{ID_MM_DEVICE_PROCESS}="1"
    LABEL="mm_whitelist_internal_modem_end"
// Apply new rules without reboot
$ sudo udevadm control --reload
$ sudo udevadm trigger
            </programlisting>
          </listitem>
          <listitem>
            <para><emphasis>MM_FILTER_RULE_EXPLICIT_BLACKLIST</emphasis></para>
            <para>
              This filter allows users to manually tag devices and/or device ports with the
              <emphasis>ID_MM_DEVICE_IGNORE</emphasis> udev tag. If the filter finds this tag,
              the device and/or device ports will be automatically ignored and port probing
              will be never run on them.
            </para>
            <programlisting>
$ sudo vim /lib/udev/rules.d/78-mm-blacklist-internal-modem.rules
    ACTION!="add|change|move", GOTO="mm_blacklist_internal_modem_end"
    ATTRS{idVendor}=="1199", ATTRS{idProduct}=="a001", ENV{ID_MM_DEVICE_IGNORE}="1"
    LABEL="mm_blacklist_internal_modem_end"
// Apply new rules without reboot
$ sudo udevadm control --reload
$ sudo udevadm trigger
            </programlisting>
          </listitem>
          <listitem>
            <para><emphasis>MM_FILTER_RULE_VIRTUAL</emphasis></para>
            <para>
              This filter will automatically flag as forbidden all ports exposed by virtual
              devices, like the 'lo' network interface or the tty0, tty1... virtual terminals.
              There is no reason to disable this filter, except for testing purposes.
            </para>
          </listitem>
          <listitem>
            <para><emphasis>MM_FILTER_RULE_NET</emphasis></para>
            <para>
              This filter will automatically flag as allowed all network ports exposed by
              devices. Unless there is a will to explicitly forbid network ports, this filter
              should always be enabled.
            </para>
          </listitem>
          <listitem>
            <para><emphasis>MM_FILTER_RULE_CDC_WDM</emphasis></para>
            <para>
              This filter will automatically flag as allowed all cdc-wdm ports exposed by
              devices. Unless there is a will to explicitly forbid the cdc-wdm ports exposed
              by qmi_wwan, cdc_mbim or huawei-cdc-ncm kernel drivers, this filter should always
              be enabled.
            </para>
          </listitem>
          <listitem>
            <para><emphasis>MM_FILTER_RULE_TTY, MM_FILTER_RULE_TTY_DEFAULT_ALLOWED and MM_FILTER_RULE_TTY_DEFAULT_FORBIDDEN</emphasis></para>
            <para>
              If the MM_FILTER_RULE_TTY filter is disabled, no TTY port will be allowed. If this
              filter is enabled, TTY ports will only be allowed if the TTY-specific filters (defined
              next) allow it.
            </para>
            <para>
              The MM_FILTER_RULE_TTY_DEFAULT_ALLOWED and MM_FILTER_RULE_TTY_DEFAULT_FORBIDDEN rules allow
              defining what happens when a TTY port isn't explicitly forbidden or accepted by any of
              the TTY-specific filters. When MM_FILTER_RULE_TTY is enabled, one of these other two options
              must be set.
            </para>
          </listitem>
          <listitem>
            <para><emphasis>MM_FILTER_RULE_TTY_BLACKLIST</emphasis></para>
            <para>
              This filter will not allow probing any of the devices flagged as
              <emphasis>ID_MM_TTY_BLACKLIST</emphasis>, like the ones in the default blacklist
              shipped by ModemManager.
            </para>
          </listitem>
          <listitem>
            <para><emphasis>MM_FILTER_RULE_TTY_MANUAL_SCAN_ONLY</emphasis></para>
            <para>
              This filter will not allow automatic probing any of the devices flagged as
              <emphasis>ID_MM_TTY_MANUAL_SCAN_ONLY</emphasis>, like the ones in the default
              USB serial adapters greylist shipped by ModemManager. Devices flagged like
              this will only be probed when a manual scan is requested via the
              <link linkend="gdbus-method-org-freedesktop-ModemManager1.ScanDevices">ScanDevices</link>
              method.
            </para>
          </listitem>
          <listitem>
            <para><emphasis>MM_FILTER_RULE_TTY_PLATFORM_DRIVER</emphasis></para>
            <para>
              If this filter is enabled, all platform TTY ports not explicitly flagged with the
              <emphasis>ID_MM_PLATFORM_DRIVER_PROBE</emphasis> will be forbidden. If the flag
              is found in a platform TTY port, port probing will be allowed directly.
            </para>
            <para>
              Note that this filter is obsoleted by the more generic MM_FILTER_RULE_EXPLICIT_WHITELIST
              filter. It is maintained for backwards compatibility with older ModemManager versions.
            </para>
          </listitem>
          <listitem>
            <para><emphasis>MM_FILTER_RULE_TTY_DRIVER</emphasis></para>
            <para>
              If this filter is enabled, all TTY ports managed by modem-specific kernel drivers will be
              allowed automatically.
            </para>
          </listitem>
          <listitem>
            <para><emphasis>FILTER_RULE_TTY_ACM_INTERFACE</emphasis></para>
            <para>
              If this filter is enabled, all TTY ports managed by the cdc-acm kernel driver with
              class=2/subclass=2/protocol=1 (AT command capable ttyACM port) will be allowed
              automatically.
            </para>
          </listitem>
          <listitem>
            <para><emphasis>MM_FILTER_RULE_TTY_WITH_NET</emphasis></para>
            <para>
              If this filter is enabled, all TTY ports for devices that also expose a network
              interface port will be allowed automatically.
            </para>
          </listitem>
        </itemizedlist>
      </para>
    </section>

    <section>
      <title>Filter policies</title>

      <para>
        The predefined filter policies are:
        <itemizedlist>
          <listitem>
            <para><emphasis>Whitelist only</emphasis></para>
            <para>
              This is a policy where only the MM_FILTER_RULE_EXPLICIT_WHITELIST rule is enabled.
            </para>
            <programlisting># /usr/sbin/ModemManager --filter-policy=WHITELIST-ONLY</programlisting>
          </listitem>
          <listitem>
            <para><emphasis>Default</emphasis></para>
            <para>
              This is a policy where the following rules are enabled:
              <itemizedlist>
                <listitem>MM_FILTER_RULE_EXPLICIT_WHITELIST</listitem>
                <listitem>MM_FILTER_RULE_EXPLICIT_BLACKLIST</listitem>
                <listitem>MM_FILTER_RULE_VIRTUAL</listitem>
                <listitem>MM_FILTER_RULE_NET</listitem>
                <listitem>MM_FILTER_RULE_CDC_WDM</listitem>
                <listitem>MM_FILTER_RULE_TTY</listitem>
                <listitem>MM_FILTER_RULE_TTY_BLACKLIST</listitem>
                <listitem>MM_FILTER_RULE_TTY_MANUAL_SCAN_ONLY</listitem>
                <listitem>MM_FILTER_RULE_TTY_PLATFORM_DRIVER</listitem>
                <listitem>MM_FILTER_RULE_TTY_DEFAULT_ALLOWED</listitem>
              </itemizedlist>
            </para>
            <para>
              This policy is the default one when a different one not explicitly
              selected, and is equivalent to the way ModemManager has worked in previous
              releases. This policy is the least restrictive one, and will end up
              allowing port probing of all TTYs not explicitly blacklisted in one way
              or another.
            </para>
            <programlisting># /usr/sbin/ModemManager --filter-policy=DEFAULT</programlisting>
          </listitem>
          <listitem>
            <para><emphasis>Strict</emphasis></para>
            <para>
              This is a policy where the following rules are enabled:
              <itemizedlist>
                <listitem>MM_FILTER_RULE_EXPLICIT_WHITELIST</listitem>
                <listitem>MM_FILTER_RULE_EXPLICIT_BLACKLIST</listitem>
                <listitem>MM_FILTER_RULE_VIRTUAL</listitem>
                <listitem>MM_FILTER_RULE_NET</listitem>
                <listitem>MM_FILTER_RULE_CDC_WDM</listitem>
                <listitem>MM_FILTER_RULE_TTY</listitem>
                <listitem>MM_FILTER_RULE_TTY_PLATFORM_DRIVER</listitem>
                <listitem>MM_FILTER_RULE_TTY_DRIVER</listitem>
                <listitem>MM_FILTER_RULE_TTY_ACM_INTERFACE</listitem>
                <listitem>MM_FILTER_RULE_TTY_WITH_NET</listitem>
                <listitem>MM_FILTER_RULE_TTY_DEFAULT_FORBIDDEN</listitem>
              </itemizedlist>
            </para>
            <para>
              This policy is stricter than the default one, as by default all TTYs are
              forbidden except for the ones explicitly allowed by one of the TTY-specific
              rules. Distributions or users should use this policy if they don't want
              ModemManager to mess around with TTY ports that may not be exposed by
              actual modems.
            </para>
            <programlisting># /usr/sbin/ModemManager --filter-policy=STRICT</programlisting>
          </listitem>
          <listitem>
            <para><emphasis>Paranoid</emphasis></para>
            <para>
              This policy is a mix of the Default and Strict ones:
              <itemizedlist>
                <listitem>MM_FILTER_RULE_EXPLICIT_WHITELIST</listitem>
                <listitem>MM_FILTER_RULE_EXPLICIT_BLACKLIST</listitem>
                <listitem>MM_FILTER_RULE_VIRTUAL</listitem>
                <listitem>MM_FILTER_RULE_NET</listitem>
                <listitem>MM_FILTER_RULE_CDC_WDM</listitem>
                <listitem>MM_FILTER_RULE_TTY</listitem>
                <listitem>MM_FILTER_RULE_TTY_BLACKLIST</listitem>
                <listitem>MM_FILTER_RULE_TTY_MANUAL_SCAN_ONLY</listitem>
                <listitem>MM_FILTER_RULE_TTY_PLATFORM_DRIVER</listitem>
                <listitem>MM_FILTER_RULE_TTY_DRIVER</listitem>
                <listitem>MM_FILTER_RULE_TTY_ACM_INTERFACE</listitem>
                <listitem>MM_FILTER_RULE_TTY_WITH_NET</listitem>
                <listitem>MM_FILTER_RULE_TTY_DEFAULT_FORBIDDEN</listitem>
              </itemizedlist>
            </para>
            <para>
              This policy is equivalent to the Strict policy, but where the ModemManager
              provided blacklist and manual scan only greylist are also used. It is not
              recommended to use this option in normal setups as the blacklists may be
              obsoleted in future ModemManager versions (in favor of using the Strict
              policy as default).
            </para>
            <programlisting># /usr/sbin/ModemManager --filter-policy=PARANOID</programlisting>
          </listitem>

          <listitem>
            <para><emphasis>Custom</emphasis></para>
            <para>
              Any of the previously defined predefined policies may be modified rule per rule
              by explicitly enabling or disabling rules via environment variables.
            </para>
            <para>
              E.g. this would launch ModemManager with the Default filter policy but with all
              net and cdc-wdm ports forbidden completely:
              <programlisting>
# MM_FILTER_RULE_NET=0 \
  MM_FILTER_RULE_CDC_WDM=0 \
  /usr/sbin/ModemManager --filter-policy=DEFAULT</programlisting>
            </para>
            <para>
              E.g. this would launch ModemManager with the Whitelist-only filter policy but also
              explicitly allowing all net and cdc-wdm ports. Note that in this case, all virtual
              net ports (e.g. 'lo') are also being allowed.
              <programlisting>
# MM_FILTER_RULE_NET=1 \
  MM_FILTER_RULE_CDC_WDM=1 \
  /usr/sbin/ModemManager --filter-policy=WHITELIST-ONLY</programlisting>
            </para>
          </listitem>
        </itemizedlist>
      </para>

    </section>
  </chapter>

  <chapter id="ref-overview-modem-port-probing">
    <title>Port probing</title>
    <para>
      Whenever a new device is detected by ModemManager, port probing process will
      get started, so that we can determine which kind of ports we have, and also
      which plugin we need to use for the specific device. Devices may expose one or
      more ports, and all of them will follow the same probing logic.
    </para>
    <para>
      The whole probing process, including pre-probing and post-probing filters, is
      implemented in the core ModemManager daemon. Plugins will just configure their
      own special needs in the probing process, so that only the steps required by the
      given plugin are executed. For example, plugins which do not support RS232
      devices will not need AT-based vendor or product filters.
    </para>

    <section>
      <title>Pre-probing filters</title>
      <para>
        Pre-probing filters are those which control whether the probing, as
        requested by the specific plugin, takes place.
      </para>
      <itemizedlist>
        <listitem>
          <para><emphasis>Allowed vendor IDs</emphasis></para>
          <para>
            Plugins can provide a list of udev-reported vendor IDs to be used as
            pre-probing filters. If the vendor ID reported by the device via udev
            is found in the list provided by the plugin, port probing will be
            launched as requested by the given plugin.
          </para>
          <para>
            This filter is specified by the <type>MM_PLUGIN_ALLOWED_VENDOR_IDS</type>
            property in the <structname>MMPlugin</structname> object provided
            by the plugin.
          </para>
        </listitem>
        <listitem>
          <para><emphasis>Product IDs</emphasis></para>
          <para>
            Plugins can provide a list of udev-reported pairs of vendor and product
            IDs to be used as pre-probing filters.
          </para>
          <para>
            If the vendor ID and product ID pair reported by the device via udev is
            found in the list of 'allowed' pairs provided by the plugin, port probing
            will be launched as requested by the given plugin. This additional filter
            should be used when the plugin is expected to work only with a given
            specific product of a given vendor.
          </para>
          <para>
            If the vendor ID and product ID pair reported by the device via udev is
            found in the list of 'forbidden' pairs provided by the plugin, port probing
            will not be launched by this plugin. This additional filter
            should be used when the plugin supports all devices of a given vendor
            except for some specific ones.
          </para>
          <para>
            These filters are specified by the <type>MM_PLUGIN_ALLOWED_PRODUCT_IDS</type>
            and <type>MM_PLUGIN_FORBIDDEN_PRODUCT_IDS</type> properties in the
            <structname>MMPlugin</structname> object provided by the plugin.
          </para>
        </listitem>
        <listitem>
          <para><emphasis>Subsystems</emphasis></para>
          <para>
            Plugins can specify which subsystems they expect, so that we filter out
            any port detected with a subsystem not listed by the plugin.
          </para>
          <para>
            This filter is specified by the <type>MM_PLUGIN_ALLOWED_SUBSYSTEMS</type>
            property in the <structname>MMPlugin</structname> object provided
            by the plugin.
          </para>
        </listitem>
        <listitem>
          <para><emphasis>Drivers</emphasis></para>
          <para>
            Plugins can specify which drivers they expect, so that we filter out
            any port detected being managed by a driver not listed by the plugin.
          </para>
          <para>
            Plugins can also specify which drivers they do not expect, so that we
            filter out any port detected being managed by a driver listed by the plugin.
          </para>
          <para>
            These filters are specified by the <type>MM_PLUGIN_ALLOWED_DRIVERS</type>
            and <type>MM_PLUGIN_FORBIDDEN_DRIVERS</type> properties in the
            <structname>MMPlugin</structname> object provided by the plugin.
          </para>
        </listitem>
        <listitem>
          <para><emphasis>udev tags</emphasis></para>
          <para>
            Plugins can provide a list of udev tags, so that we filter out
            any port detected which doesn't expose any of the given tags.
          </para>
          <para>
            This filter is specified by the <type>MM_PLUGIN_ALLOWED_UDEV_TAGS</type>
            property in the <structname>MMPlugin</structname> object provided
            by the plugin.
          </para>
        </listitem>
      </itemizedlist>
    </section>

    <section>
      <title>Probing sequence</title>
      <para>
        Whenever all pre-probing filters of a given plugin pass, ModemManager will run
        the probing sequence as requested by the specific plugin. The main purpose of the
        probing sequence step is to determine the type of port being probed, and also
        prepare the information required in any expected post-probing filter.
      </para>
      <itemizedlist>
        <listitem>
          <para><emphasis>Custom initialization</emphasis></para>
          <para>
            This property allows plugins to provide an asynchronous method which will get
            executed as soon as the AT port gets opened. This method may be used for any
            purpose, like running an early command in the ports as soon as possible, or
            querying the modem for info about the port layout.
          </para>
          <para>
            This configuration is specified by the <type>MM_PLUGIN_CUSTOM_INIT</type>
            property in the <structname>MMPlugin</structname> object provided
            by the plugin.
          </para>
        </listitem>
        <listitem>
          <para><emphasis>AT allowed</emphasis></para>
          <para>
            This boolean property allows plugins to specify that they expect and support
            AT serial ports.
          </para>
          <para>
            This configuration is specified by the <type>MM_PLUGIN_ALLOWED_AT</type>
            property in the <structname>MMPlugin</structname> object provided
            by the plugin.
          </para>
        </listitem>
        <listitem>
          <para><emphasis>Single AT expected</emphasis></para>
          <para>
            This boolean property allows plugins to specify that they only expect and support
            one AT serial port. Whenever the first AT port is grabbed, any remaining AT probing
            in ports of the same device will get cancelled.
          </para>
          <para>
            This configuration is specified by the <type>MM_PLUGIN_ALLOWED_SINGLE_AT</type>
            property in the <structname>MMPlugin</structname> object provided
            by the plugin.
          </para>
        </listitem>
        <listitem>
          <para><emphasis>Custom AT probing</emphasis></para>
          <para>
            This property allows plugins to specify custom commands to check whether a port
            is AT or not. By default, the 'AT' command will be used if no custom one specified.
          </para>
          <para>
            This configuration is specified by the <type>MM_PLUGIN_CUSTOM_AT_PROBE</type>
            property in the <structname>MMPlugin</structname> object provided
            by the plugin.
          </para>
        </listitem>
        <listitem>
          <para><emphasis>QCDM allowed</emphasis></para>
          <para>
            This boolean property allows plugins to specify that they expect and support
            QCDM serial ports.
          </para>
          <para>
            This configuration is specified by the <type>MM_PLUGIN_ALLOWED_QCDM</type>
            property in the <structname>MMPlugin</structname> object provided
            by the plugin.
          </para>
        </listitem>
        <listitem>
          <para><emphasis>Check Icera support</emphasis></para>
          <para>
            This boolean property allows plugins to specify that they want to have the Icera
            support checks included in the probing sequence. They can afterwards get the result
            of the support check to decide whether they want to create a Icera-based modem
            object or not.
          </para>
          <para>
            This configuration is specified by the <type>MM_PLUGIN_ICERA_PROBE</type>
            property in the <structname>MMPlugin</structname> object provided
            by the plugin.
          </para>
        </listitem>
      </itemizedlist>
    </section>

    <section>
      <title>Post-probing filters</title>
      <para>
        Post-probing filters are required to identify whether a plugin can handle a given
        modem, in special cases where the information retrieved from udev is either not
        enough or wrong. This covers, for example, RS232 modems connected through a RS232
        to USB converter, where udev-reported vendor ID is that of the converter, not the
        one of the modem.
      </para>
      <itemizedlist>
        <listitem>
          <para><emphasis>Allowed vendor strings</emphasis></para>
          <para>
            Plugins can provide a list of vendor strings to be used as post-probing
            filters. If the vendor string reported by the device via AT commands
            is found in the list provided by the plugin, the plugin will report that
            it can handle this modem.
          </para>
          <para>
            This filter is specified by the <type>MM_PLUGIN_ALLOWED_VENDOR_STRINGS</type>
            property in the <structname>MMPlugin</structname> object provided
            by the plugin.
          </para>
        </listitem>
        <listitem>
          <para><emphasis>Product strings</emphasis></para>
          <para>
            Plugins can provide a list of pairs of vendor and product
            strings to be used as post-probing filters.
          </para>
          <para>
            If the vendor and product string pair reported by the device via AT
            commands is found in the 'allowed' list provided by the plugin, the
            plugin will report that it can handle this modem. This additional filter
            should be used when the plugin is expected to work only with a given
            specific product of a given vendor.
          </para>
          <para>
            If the vendor and product string pair reported by the device via AT
            commands is found in the 'forbidden list provided by the plugin, the
            plugin will report that it cannot handle this modem. This additional filter
            should be used when the plugin supports all devices of a given vendor, except for some specific ones.
          </para>
          <para>
            These filters are specified by the <type>MM_PLUGIN_ALLOWED_PRODUCT_STRINGS</type>
            and <type>MM_PLUGIN_FORBIDDEN_PRODUCT_STRINGS</type> properties in the
            <structname>MMPlugin</structname> object provided by the plugin.
          </para>
        </listitem>
        <listitem>
          <para><emphasis>Icera support</emphasis></para>
          <para>
            Plugins can specify that they only support Icera-based modems, or that they
            do not support any Icera-based modem. When either of this configurations is
            enabled, the Icera support checks will be included in the
            probing sequence, and the result of the check will help to determine whether
            the plugin supports the modem or not.
          </para>
          <para>
            This filter is specified by the <type>MM_PLUGIN_ALLOWED_ICERA</type> and
            <type>MM_PLUGIN_FORBIDDEN_ICERA</type> properties in the
            <structname>MMPlugin</structname> object provided by the plugin.
          </para>
        </listitem>
      </itemizedlist>

      <note>
        <para>
          Plugins which require post-probing filters will always be sorted last, and
          therefore they will be the last ones being checked for pre-probing filters. This
          is due to the fact that we need to assume that these plugins aren't able to
          determine port support just with pre-probing filters, as we want to avoid
          unnecessary probing sequences launched. Also note that the Generic plugin is
          anyway always the last one in the list.
        </para>
      </note>
    </section>

    <section>
      <title>Probing setup examples</title>
      <example>
        <title>Probing setup for a plugin requiring udev-based vendor/product checks</title>
        <programlisting>
G_MODULE_EXPORT MMPlugin *
mm_plugin_create (void)
{
    static const gchar *subsystems[] = { "tty", NULL };
    static const guint16 vendor_ids[] = { 0xabcd, 0 };
    static const mm_uint16_pair product_ids[] = {
        { 0x1234, 0xffff }
    };
    static const gchar *vendor_strings[] = { "vendor", NULL };

    return MM_PLUGIN (
        g_object_new (MM_TYPE_PLUGIN_IRIDIUM,
                      MM_PLUGIN_NAME, "Example",

                      /* Next items are pre-probing filters */
                      MM_PLUGIN_ALLOWED_SUBSYSTEMS, subsystems,
                      MM_PLUGIN_ALLOWED_VENDOR_IDS, vendor_ids,
                      MM_PLUGIN_ALLOWED_PRODUCT_IDS, product_ids,

                      /* Next items are probing sequence setup */
                      MM_PLUGIN_ALLOWED_AT, TRUE,

                      /* No post-probing filters */
                      NULL));
}
        </programlisting>
      </example>

      <example>
        <title>Probing setup for a plugin requiring AT-probed vendor/product checks</title>
        <programlisting>
G_MODULE_EXPORT MMPlugin *
mm_plugin_create (void)
{
    static const gchar *subsystems[] = { "tty", NULL };
    static const gchar *vendor_strings[] = { "vendor", NULL };
    static const mm_str_pair product_strings[] = { "another-vendor", "product xyz" };

    return MM_PLUGIN (
        g_object_new (MM_TYPE_PLUGIN_IRIDIUM,
                      MM_PLUGIN_NAME, "Example",

                      /* Next items are pre-probing filters */
                      MM_PLUGIN_ALLOWED_SUBSYSTEMS, subsystems,

                      /* Next items are probing sequence setup */
                      MM_PLUGIN_ALLOWED_AT, TRUE,

                      /* Next items are post-probing filters */
                      MM_PLUGIN_VENDOR_STRINGS, vendor_strings,
                      MM_PLUGIN_PRODUCT_STRINGS, product_strings,
                      NULL));
}
        </programlisting>
      </example>

      <example>
        <title>Probing setup for a plugin with custom initialization requirements</title>
        <programlisting>
static gboolean
parse_custom_at (const gchar *response,
                 const GError *error,
                 GValue *result,
                 GError **result_error)
{
    if (error) {
        *result_error = g_error_copy (error);
        return FALSE;
    }

    /* Otherwise, done. And also report that it's an AT port. */
    g_value_init (result, G_TYPE_BOOLEAN);
    g_value_set_boolean (result, TRUE);
    return TRUE;
}

static const MMPortProbeAtCommand custom_at_probe[] = {
    { "AT+SOMETHING", parse_custom_at },
    { NULL }
};

G_MODULE_EXPORT MMPlugin *
mm_plugin_create (void)
{
    static const gchar *subsystems[] = { "tty", NULL };
    static const guint16 vendor_ids[] = { 0xabcd, 0 };

    return MM_PLUGIN (
        g_object_new (MM_TYPE_PLUGIN_EXAMPLE,
                      MM_PLUGIN_NAME, "Example",

                      /* Next items are pre-probing filters */
                      MM_PLUGIN_ALLOWED_SUBSYSTEMS, subsystems,
                      MM_PLUGIN_ALLOWED_VENDOR_IDS, vendor_ids,

                      /* Next items are probing sequence setup */
                      MM_PLUGIN_CUSTOM_AT_PROBE, custom_at_probe,
                      MM_PLUGIN_ALLOWED_AT,      TRUE,

                      /* No post-probing filters */
                      NULL));
}
        </programlisting>
      </example>
    </section>
  </chapter>

  <chapter id="ref-overview-modem-object-creation">
    <title>Modem object creation</title>
    <para>
      Once a port passes all probing filters of a given plugin, the plugin will grab
      the port. When the first port of a given device is grabbed, the plugin will create
      the required Modem object.
    </para>
    <para>
      While preparing to get the Modem object grab the specific port probed, udev-based
      port type hints can be used to specify AT port flags (e.g. if a port is to be
      considered primary, secondary or for PPP).
    </para>
  </chapter>

  <chapter id="ref-overview-modem-state-machine">
    <title>Modem state machine</title>
    <para>
      Once all ports of a given modem have been probed and grabbed by a newly created
      Modem object, ModemManager will start the global state machine for the modem, as
      defined in the picture below.
    </para>
    <figure id="mm-modemmanager-states">
      <title>ModemManager states</title>
      <graphic fileref="ModemManager-states.png" format="PNG"></graphic>
    </figure>
    <para>
      The state machine of a modem can be summarized in 5 main sequences:
      initialization, enabling, connection, disconnection and disabling.
    </para>

    <section>
      <title>Initialization</title>
      <para>
        The modem initialization sequence starts only when all ports
        have been probed and grabbed by a given plugin. This is done so that the proper
        AT port (that suggested to be Primary) is used as control port.
      </para>
      <para>
        The global initialization sequence is itself splitted into N per-interface
        initialization steps (being N the number of interfaces implemented by the
        modem object). The following list provides the steps required in the
        initialization sequence of a Broadband modem object.
      </para>
      <itemizedlist>
        <listitem>
          <para><emphasis>Modem interface initialization</emphasis></para>
          <para>
            The <link linkend="gdbus-org.freedesktop.ModemManager1.Modem">Modem interface</link>
            provides common actions and information available in the majority of the modems
            (including Broadband-specific items which won't be implemented by POTS modems).
          </para>
          <para>
            One of the key things done during the initialization of this interface is the
            <emphasis>checking of supported capabilities</emphasis>. Broadband modem objects
            are able to handle 3GPP-only, CDMA-only and mixed 3GPP+CDMA modems, but in order
            to properly handle the distinctions required in these, ModemManager first needs
            to know exactly which is the current set of capabilities.
          </para>
          <para>
            The other key step in this sequence involves <emphasis>checking the lock status
            of the modem and/or SIM </emphasis>. If the modem/SIM is found to be locked, the
            whole initialization sequence is halted and the modem is left in a locked state
            until unlocked by the user. Note, therefore, that modems that are locked will not
            expose additional feature-specific DBus interfaces until they get unlocked.
          </para>
          <note>
            <para>
              It may be the case that some of the steps in the initialization of the Modem
              interface require the modem itself to be unlocked. If the modem is found locked
              during the first initialization attempt, as soon as it gets unlocked the
              initialization sequence will be re-executed.
            </para>
          </note>
        </listitem>
        <listitem>
          <emphasis>3GPP interface initialization</emphasis>
          <para>
            The <link linkend="gdbus-org.freedesktop.ModemManager1.Modem.Modem3gpp">3GPP interface</link>
            provides common actions and setup for modems which provide 3GPP capabilities. Therefore,
            this interface initialization sequence will only be run in 3GPP-enabled modems.
          </para>
        </listitem>
        <listitem>
          <emphasis>CDMA interface initialization</emphasis>
          <para>
            The <link linkend="gdbus-org.freedesktop.ModemManager1.Modem.ModemCdma">CDMA interface</link>
            provides common actions and setup for modems which provide CDMA capabilities. Therefore,
            this interface initialization sequence will only be run in CDMA-enabled modems.
          </para>
        </listitem>
        <listitem>
          <para><emphasis>Additional feature-specific interface initializations</emphasis></para>
          <para>
            Modems with additional features will export feature-specific interfaces, such as
            the <link linkend="gdbus-org.freedesktop.ModemManager1.Modem.Location">Location</link> or
            the <link linkend="gdbus-org.freedesktop.ModemManager1.Modem.Messaging">Messaging</link>
            ones.
          </para>
          <para>
            These interfaces also have their own initialization sequences, where the first step
            in the sequence is always the check of whether the given modem supports the given feature.
            In other words, modems will only end up exporting the interfaces for the features they
            support.
          </para>
        </listitem>
      </itemizedlist>
    </section>

    <section>
      <title>Enabling</title>
      <para>
        Modem enabling is the user-requested sequence with the sole purpose of bringing
        the modem to a state where it can get connected.
      </para>
      <para>
        As with the initialization sequence, the global enabling sequence is itself
        splitted into N per-interface enabling steps (being N the number of interfaces
        exported by the modem). Those interfaces implemented by the object but not
        supported by the modem will not be enabled.
      </para>
      <itemizedlist>
        <listitem>
          <para><emphasis>Modem interface enabling</emphasis></para>
          <para>
            The sequence to enable the
            <link linkend="gdbus-org.freedesktop.ModemManager1.Modem">Modem interface</link>
            takes care of different important steps, such as <emphasis>powering up the
            radio interface</emphasis> or <emphasis>configuring</emphasis> the best charset
            to use.
          </para>
        </listitem>
        <listitem>
          <para><emphasis>3GPP interface enabling</emphasis></para>
          <para>
            Modems with 3GPP capabilities will enable the
            <link linkend="gdbus-org.freedesktop.ModemManager1.Modem.Modem3gpp">3GPP interface</link>
            as part of the global enabling sequence. This sequence involves setting up the
            <emphasis>automatic registration</emphasis> of the device in the network, as well
            as configuring 3GPP specific <emphasis>indicators and unsolicited message
            handlers</emphasis>.
          </para>
        </listitem>
        <listitem>
          <para><emphasis>CDMA interface enabling</emphasis></para>
          <para>
            Modems with CDMA capabilities will enable the
            <link linkend="gdbus-org.freedesktop.ModemManager1.Modem.ModemCdma">CDMA interface</link>
            as part of the global enabling sequence. This sequence involves setting up the
            <emphasis>periodic checks of registration</emphasis> in the CDMA network.
          </para>
        </listitem>
        <listitem>
          <para><emphasis>Additional feature-specific interface enablings</emphasis></para>
          <para>
            Each feature-specific interface will have its own enabling sequence, with operations
            which are directly related to the purpose of the interface. For example, enabling the
            <link linkend="gdbus-org.freedesktop.ModemManager1.Modem.Location">Location</link>
            interface will involve setting up the initial location information; and enabling the
            <link linkend="gdbus-org.freedesktop.ModemManager1.Modem.Messaging">Messaging</link>
            interface will involve loading the initial list of SMS available in the SIM or Modem.
          </para>
        </listitem>
      </itemizedlist>
    </section>

    <section>
      <title>Connection &amp; disconnection</title>
      <para>
        Connecting the Modem is done through the <emphasis>Bearer</emphasis> objects. Once such an
        object is created, the user can request to get the given bearer connected.
      </para>
      <para>
        Broadband Modems will usually create Broadband Bearers. This kind of bearers can run either
        the CDMA connection sequence (if the modem has CDMA capabilities) or the 3GPP connection
        sequence (if the modem has 3GPP capabilities). For the special case of mixed 3GPP+CDMA
        modems, it is assumed that the plugin implementation needs to decide how the connection gets
        done. By default, anyway, the 3GPP sequence is used in this case.
      </para>
      <note>
        <para>
          Modems which are both LTE (3GPP) and CDMA can hand over from LTE to CDMA transparently and
          automatically when no LTE network is available, even keeping the same IP address. When this
          happens, the modem will get notified about the access technology change, and ModemManager
          will update that information.
        </para>
      </note>
    </section>

    <section>
      <title>Disabling</title>
      <para>
        Users can disable the modems, which will bring them to a state where they are in low power
        mode (e.g. RF switched off) and not registered in any network.
      </para>
      <para>
        As with the initialization or enabling sequences, the global disabling sequence is itself
        splitted into N per-interface disabling steps (being N the number of interfaces
        exported by the modem). Those interfaces implemented by the object but not
        supported by the modem will not be disabled.
      </para>
      <note>
        <para>
          The global disabling sequence will go on disabling the interfaces one by one, but
          starting with the interface which was last enabled during the enabling sequence, and
          backwards. This ensures that the
          <link linkend="gdbus-org.freedesktop.ModemManager1.Modem">Modem interface</link>
          gets disabled last.
        </para>
      </note>
      <itemizedlist>
        <listitem>
          <para><emphasis>Additional feature-specific interface disablings</emphasis></para>
          <para>
            Each feature-specific interface will have its own disabling sequence, with operations
            which are directly related to the purpose of the interface. For example, disabling the
            <link linkend="gdbus-org.freedesktop.ModemManager1.Modem.Location">Location</link>
            interface will involve shutting down the location gathering; and disabling the
            <link linkend="gdbus-org.freedesktop.ModemManager1.Modem.Messaging">Messaging</link>
            interface will involve unexporting all SMS objects from DBus.
          </para>
        </listitem>
        <listitem>
          <para><emphasis>CDMA interface disabling</emphasis></para>
          <para>
            Modems with CDMA capabilities will disable the
            <link linkend="gdbus-org.freedesktop.ModemManager1.Modem.ModemCdma">CDMA interface</link>
            as part of the global disabling sequence. This sequence involves cancelling the
            <emphasis>periodic checks of registration</emphasis> in the CDMA network.
          </para>
        </listitem>
        <listitem>
          <para><emphasis>3GPP interface disabling</emphasis></para>
          <para>
            Modems with 3GPP capabilities will disable the
            <link linkend="gdbus-org.freedesktop.ModemManager1.Modem.Modem3gpp">3GPP interface</link>
            as part of the global disabling sequence. This sequence involves, among other things,
            cleaning up 3GPP specific <emphasis>indicators and unsolicited message handlers</emphasis>.
          </para>
        </listitem>
        <listitem>
          <para><emphasis>Modem interface disabling</emphasis></para>
          <para>
            The sequence to disable the
            <link linkend="gdbus-org.freedesktop.ModemManager1.Modem">Modem interface</link>
            takes care of different important steps, such as <emphasis>powering down the
            radio interface</emphasis>.
          </para>
        </listitem>

      </itemizedlist>
    </section>
  </chapter>

  <chapter id="ref-overview-plugin-specific-modems">
    <title>Plugin-specific Modems</title>
    <para>
      ModemManager plugins exist in order to handle all non-standard vendor-specific behaviour
      that needs to get supported.
    </para>
    <para>
      Plugins will provide their own Modem object implementations, usually subclassing the
      generic <structname>MMBroadbandModem</structname> object. As previously explained, this
      object implements every interface that may be exported by the Modem object in DBus; and
      then, depending on the per-interface support checks, the interface will end up being
      really exported or not.
    </para>
    <para>
      Each interface defines every step to be run during the initialization, enabling or
      disabling sequences. Then, the object implementing the interface may or may not provide
      the implementation of such step. By default, the generic
      <structname>MMBroadbandModem</structname> object implements already most of the steps
      in the interfaces providing common features:
    </para>
    <figure id="mm-modemmanager-interface-initialization-sequence">
      <title>Modem interface initialization sequence</title>
      <graphic fileref="ModemManager-interface-initialization-sequence.png" format="PNG"></graphic>
    </figure>
    <para>
      Vendor-specific subclasses of <structname>MMBroadbandModem</structname> are then able to
      either provide their own implementation of a given step (in the image below, a custom
      implementation for capabilities checking); or even completely disable the step if they
      know that there is no way to run it (in the image below, revision string loading is
      removed).
    </para>
    <figure id="mm-modemmanager-interface-initialization-sequence-subclassed">
      <title>Modem interface initialization sequence subclassed</title>
      <graphic fileref="ModemManager-interface-initialization-sequence-subclassed.png" format="PNG"></graphic>
    </figure>
    <para>
      These subclass-able steps are all implemented as standard GIO asynchronous functions,
      so subclassing a step involves implementing both the async method which receives the
      input arguments to the action and the corresponding <literal>_finish()</literal> method
      which provides the results of the action once the operation is ready.
    </para>
    <para>
      It is worth noting that these steps and the asynchronous methods implementing them
      don't assume that an AT port will be used to implement the real action. This means
      that any other kind of port may be really used (e.g. QCDM or QMI) in the implementation,
      or even that a static reply can be returned (e.g. Iridium modems will always report
      "Iridium" as current OperatorName).
    </para>
  </chapter>
</part>