man: various documentation improvements for sd-bus

man/sd_bus_default.xml

@@ -109,26 +109,30 @@
     <title>Description</title>
 
     <para><function>sd_bus_default()</function> acquires a bus
-    connection object to the user bus when invoked in user context or
+    connection object to the user bus when invoked in user context, or
     to the system bus otherwise. The connection object is associated
     to the calling thread. Each time the function is invoked from the
     same thread the same object is returned, but its reference count
-    increased by one, as long as at least one reference is kept. When
+    is increased by one, as long as at least one reference is
-    the last reference to the connection is dropped (using the
+    kept. When the last reference to the connection is dropped (using
-    <function>sd_bus_unref()</function> call), the connection is
+    the
-    terminated. Note that the connection is not automatically
+    <citerefentry><refentrytitle>sd_bus_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>
-    terminated when the associated thread ends. It is important to
+    call), the connection is terminated. Note that the connection is
-    drop the last reference to the bus connection explicitly before
+    not automatically terminated when the associated thread ends. It
-    the thread ends or otherwise the connection will be leaked.</para>
+    is important to drop the last reference to the bus connection
+    explicitly before the thread ends or otherwise the connection will
+    be leaked.</para>
 
     <para><function>sd_bus_default_user()</function> returns a user
     bus connection object associated to the calling thread.
     <function>sd_bus_default_system()</function> is similar, but
-    connects to the system bus.</para>
+    connects to the system bus. Note that
+    <function>sd_bus_default()</function> is identical to these two
+    calls, depending on the execution context.</para>
 
     <para><function>sd_bus_open()</function> creates a new,
     independent bus connection to the user bus when invoked in user
-    context or the system bus
+    context, or the system bus
     otherwise. <function>sd_bus_open_user()</function> is similar, but
     connects only to the user bus.
     <function>sd_bus_open_system()</function> does the same, but
@@ -162,8 +166,10 @@
 
     <para><function>sd_bus_open_system_remote()</function> connects to
     the system bus on the specified <parameter>host</parameter> using
-    SSH. <parameter>host</parameter> consists of an optional user name
+    <citerefentry
-    followed by the <literal>@</literal> symbol, and the hostname.
+    project='die-net'><refentrytitle>ssh</refentrytitle><manvolnum>1</manvolnum></citerefentry>. <parameter>host</parameter>
+    consists of an optional user name followed by the
+    <literal>@</literal> symbol, and the hostname.
     </para>
 
     <para><function>sd_bus_open_system_container()</function> connects
@@ -171,7 +177,18 @@
     where <parameter>machine</parameter> is the name of a local
     container.  See
     <citerefentry><refentrytitle>machinectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
-    for more information about "machines".</para>
+    for more information about the "machine" concept. Note that
+    connections into local containers are only available to privileged
+    processes at this time.</para>
+
+    <para>These calls allocate a bus connection object and initiate
+    the connection ot a well-known bus of some form. An alternative to
+    using these high-level calls is to create an unconnected bus
+    object with
+    <citerefentry><refentrytitle>sd_bus_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+    and to connect it with
+    <citerefentry><refentrytitle>sd_bus_start</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
+    </para>
 
   </refsect1>
 
@@ -185,8 +202,8 @@
 
   <refsect1>
     <title>Reference ownership</title>
-    <para>The functions <function>sd_bus_open_user()</function>,
+    <para>The functions <function>sd_bus_open()</function>,
-    <function>sd_bus_open()</function>,
+    <function>sd_bus_open_user()</function>,
     <function>sd_bus_open_system()</function>,
     <function>sd_bus_open_system_remote()</function>, and
     <function>sd_bus_open_system_machine()</function> return a new

man/sd_bus_negotiate_fds.xml

@@ -70,7 +70,7 @@
         <funcdef>int <function>sd_bus_negotiate_creds</function></funcdef>
         <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
         <paramdef>int <parameter>b</parameter></paramdef>
-        <paramdef>uint64_t <parameter>flags</parameter></paramdef>
+        <paramdef>uint64_t <parameter>mask</parameter></paramdef>
       </funcprototype>
     </funcsynopsis>
   </refsynopsisdiv>
@@ -81,10 +81,11 @@
     <para><function>sd_bus_negotiate_fds()</function> controls whether
     file descriptor passing shall be negotiated for the specified bus
     connection. It takes a bus object and a boolean, which, when true,
-    enables file descriptor passing, and, when false, disables it. Note
+    enables file descriptor passing, and, when false, disables
-    that not all transports and servers support file descriptor
+    it. Note that not all transports and servers support file
-    passing. To find out whether file descriptor passing is available
+    descriptor passing. In particular, networked transports generally
-    after negotiation, use
+    do not support file descriptor passing. To find out whether file
+    descriptor passing is available after negotiation, use
     <citerefentry><refentrytitle>sd_bus_can_send</refentrytitle><manvolnum>3</manvolnum></citerefentry>
     and pass <constant>SD_BUS_TYPE_UNIX_FD</constant>. Note that file
     descriptor passing is always enabled for both sending and
@@ -101,34 +102,44 @@
     <para><function>sd_bus_negotiate_timestamps()</function> controls
     whether implicit sender timestamps shall be attached automatically
     to all incoming messages. Takes a bus object and a boolean, which,
-    when true, enables timestamping, and, when false, disables it. If
+    when true, enables timestamping, and, when false, disables it.
-    this is disabled,
+    Use
     <citerefentry><refentrytitle>sd_bus_message_get_monotonic_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
     <citerefentry><refentrytitle>sd_bus_message_get_realtime_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
     <citerefentry><refentrytitle>sd_bus_message_get_seqnum</refentrytitle><manvolnum>3</manvolnum></citerefentry>
-    fail with <constant>-ENODATA</constant> on incoming messages. Note
+    to query the timestamps of incoming messages. If negotiation is
-    that not all transports support timestamping of messages. On local
+    disabled or not supported these calls will fail with
-    transports, the timestamping is applied by the kernel and cannot
+    <constant>-ENODATA</constant>. Note that not all transports
-    be manipulated by userspace. By default, message timestamping is
+    support timestamping of messages. Specifically, timestamping is
-    not negotiated for all connections.</para>
+    only available on the kdbus transport, but not on dbus1. The
+    timestamping is applied by the kernel and cannot be manipulated by
+    userspace. By default, message timestamping is not negotiated for
+    connections.</para>
 
     <para><function>sd_bus_negotiate_creds()</function> controls
-    whether implicit sender credentials shall be attached
+    whether and which implicit sender credentials shall be attached
     automatically to all incoming messages. Takes a bus object, a
     boolean indicating whether to enable or disable the credential
     parts encoded in the bit mask value argument. Note that not all
     transports support attaching sender credentials to messages, or do
     not support all types of sender credential parameters, or might
     suppress them under certain circumstances for individual
-    messages. On local transports, the sender credentials are attached
+    messages. Specifically, implicit sender credentials on messages
-    by the kernel and cannot be manipulated by userspace. By default,
+    are only fully supported on kdbus transports, and dbus1 only
-    no sender credentials are attached.</para>
+    supports <constant>SD_BUS_CREDS_UNIQUE_NAME</constant>. The sender
+    credentials are attached by the kernel and cannot be manipulated
+    by userspace, and are thus suitable for authorization
+    decisions. By default, only
+    <constant>SD_BUS_CREDS_WELL_KNOWN_NAMES</constant> and
+    <constant>SD_BUS_CREDS_UNIQUE_NAME</constant> are enabled. In
+    fact, these two credential fields are always sent along and cannot
+    be turned off.</para>
 
     <para>The <function>sd_bus_negotiate_fds()</function> function may
     be called only before the connection has been started with
     <citerefentry><refentrytitle>sd_bus_start</refentrytitle><manvolnum>3</manvolnum></citerefentry>. Both
     <function>sd_bus_negotiate_timestamp()</function> and
-    <function>sd_bus_negotiate_creds()</function> also may be called
+    <function>sd_bus_negotiate_creds()</function> may also be called
     after a connection has been set up. Note that when operating on a
     connection that is shared between multiple components of the same
     program (for example via
@@ -163,7 +174,7 @@
   <refsect1>
     <title>Notes</title>
 
-    <para><function>sd_bus_negotiate_fs()</function> and the other
+    <para><function>sd_bus_negotiate_fds()</function> and the other
     functions described here are available as a shared library, which
     can be compiled and linked to with the
     <constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
@@ -179,6 +190,8 @@
       <citerefentry><refentrytitle>sd_bus_start</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
       <citerefentry><refentrytitle>sd_bus_message_can_send</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
       <citerefentry><refentrytitle>sd_bus_message_get_monotonic_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>sd_bus_message_get_realtime_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>sd_bus_message_get_seqnum</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
       <citerefentry><refentrytitle>sd_bus_message_get_creds</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
       <citerefentry><refentrytitle>systemd.busname</refentrytitle><manvolnum>5</manvolnum></citerefentry>
     </para>

man/sd_bus_new.xml

@@ -77,7 +77,21 @@
     <para><function>sd_bus_new()</function> creates a new bus
     object. This object is reference-counted, and will be destroyed
     when all references are gone. Initially, the caller of this
-    function owns the sole reference.</para>
+    function owns the sole reference. The bus object will not be
+    connected to any bus initially. To connect it to a bus, make sure
+    to set an address with
+    <citerefentry><refentrytitle>sd_bus_set_address</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+    or a related call, and then start the connection with
+    <citerefentry><refentrytitle>sd_bus_start</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
+
+    <para>In most cases it's a better idea to invoke
+    <citerefentry><refentrytitle>sd_bus_default_user</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+    <citerefentry><refentrytitle>sd_bus_default_system</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+    or related calls instead of the more low-level
+    <function>sd_bus_new()</function> and
+    <function>sd_bus_start()</function>. The higher-level calls not
+    only allocate a bus object but also start the connection to a
+    well-known bus in a single function invocation.</para>
 
     <para><function>sd_bus_ref()</function> creates a new reference to
     <parameter>bus</parameter>. This bus object will not be destroyed
@@ -135,10 +149,10 @@
     <para>
       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
       <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
-      <citerefentry><refentrytitle>sd_bus_open_user</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
-      <citerefentry><refentrytitle>sd_bus_open_system</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
       <citerefentry><refentrytitle>sd_bus_default_user</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
-      <citerefentry><refentrytitle>sd_bus_default_system</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+      <citerefentry><refentrytitle>sd_bus_default_system</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>sd_bus_open_user</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>sd_bus_open_system</refentrytitle><manvolnum>3</manvolnum></citerefentry>
     </para>
   </refsect1>