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Diffstat (limited to 'Documentation/kdbus/kdbus.bus.xml')
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diff --git a/Documentation/kdbus/kdbus.bus.xml b/Documentation/kdbus/kdbus.bus.xml new file mode 100644 index 000000000..83f1198bc --- /dev/null +++ b/Documentation/kdbus/kdbus.bus.xml @@ -0,0 +1,344 @@ +<?xml version='1.0'?> <!--*-nxml-*--> +<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" + "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> + +<refentry id="kdbus.bus"> + + <refentryinfo> + <title>kdbus.bus</title> + <productname>kdbus.bus</productname> + </refentryinfo> + + <refmeta> + <refentrytitle>kdbus.bus</refentrytitle> + <manvolnum>7</manvolnum> + </refmeta> + + <refnamediv> + <refname>kdbus.bus</refname> + <refpurpose>kdbus bus</refpurpose> + </refnamediv> + + <refsect1> + <title>Description</title> + + <para> + A bus is a resource that is shared between connections in order to + transmit messages (see + <citerefentry> + <refentrytitle>kdbus.message</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry>). + Each bus is independent, and operations on the bus will not have any + effect on other buses. A bus is a management entity that controls the + addresses of its connections, their policies and message transactions + performed via this bus. + </para> + <para> + Each bus is bound to the mount instance it was created on. It has a + custom name that is unique across all buses of a domain. In + <citerefentry> + <refentrytitle>kdbus.fs</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + a bus is presented as a directory. No operations can be performed on + the bus itself; instead you need to perform the operations on an endpoint + associated with the bus. Endpoints are accessible as files underneath the + bus directory. A default endpoint called <constant>bus</constant> is + provided on each bus. + </para> + <para> + Bus names may be chosen freely except for one restriction: the name must + be prefixed with the numeric effective UID of the creator and a dash. This + is required to avoid namespace clashes between different users. When + creating a bus, the name that is passed in must be properly formatted, or + the kernel will refuse creation of the bus. Example: + <literal>1047-foobar</literal> is an acceptable name for a bus + registered by a user with UID 1047. However, + <literal>1024-foobar</literal> is not, and neither is + <literal>foobar</literal>. The UID must be provided in the + user-namespace of the bus owner. + </para> + <para> + To create a new bus, you need to open the control file of a domain and + employ the <constant>KDBUS_CMD_BUS_MAKE</constant> ioctl. The control + file descriptor that was used to issue + <constant>KDBUS_CMD_BUS_MAKE</constant> must not previously have been + used for any other control-ioctl and must be kept open for the entire + life-time of the created bus. Closing it will immediately cleanup the + entire bus and all its associated resources and endpoints. Every control + file descriptor can only be used to create a single new bus; from that + point on, it is not used for any further communication until the final + <citerefentry> + <refentrytitle>close</refentrytitle> + <manvolnum>2</manvolnum> + </citerefentry> + . + </para> + <para> + Each bus will generate a random, 128-bit UUID upon creation. This UUID + will be returned to creators of connections through + <varname>kdbus_cmd_hello.id128</varname> and can be used to uniquely + identify buses, even across different machines or containers. The UUID + will have its variant bits set to <literal>DCE</literal>, and denote + version 4 (random). For more details on UUIDs, see <ulink + url="https://en.wikipedia.org/wiki/Universally_unique_identifier"> + the Wikipedia article on UUIDs</ulink>. + </para> + + </refsect1> + + <refsect1> + <title>Creating buses</title> + <para> + To create a new bus, the <constant>KDBUS_CMD_BUS_MAKE</constant> + command is used. It takes a <type>struct kdbus_cmd</type> argument. + </para> + <programlisting> +struct kdbus_cmd { + __u64 size; + __u64 flags; + __u64 return_flags; + struct kdbus_item items[0]; +}; + </programlisting> + + <para>The fields in this struct are described below.</para> + + <variablelist> + <varlistentry> + <term><varname>size</varname></term> + <listitem><para> + The overall size of the struct, including its items. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>flags</varname></term> + <listitem><para>The flags for creation.</para> + <variablelist> + <varlistentry> + <term><constant>KDBUS_MAKE_ACCESS_GROUP</constant></term> + <listitem> + <para>Make the bus file group-accessible.</para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_MAKE_ACCESS_WORLD</constant></term> + <listitem> + <para>Make the bus file world-accessible.</para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_FLAG_NEGOTIATE</constant></term> + <listitem> + <para> + Requests a set of valid flags for this ioctl. When this bit is + set, no action is taken; the ioctl will return + <errorcode>0</errorcode>, and the <varname>flags</varname> + field will have all bits set that are valid for this command. + The <constant>KDBUS_FLAG_NEGOTIATE</constant> bit will be + cleared by the operation. + </para> + </listitem> + </varlistentry> + </variablelist> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>return_flags</varname></term> + <listitem><para> + Flags returned by the kernel. Currently unused and always set to + <constant>0</constant> by the kernel. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>items</varname></term> + <listitem> + <para> + The following items (see + <citerefentry> + <refentrytitle>kdbus.item</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry>) + are expected for <constant>KDBUS_CMD_BUS_MAKE</constant>. + </para> + <variablelist> + <varlistentry> + <term><constant>KDBUS_ITEM_MAKE_NAME</constant></term> + <listitem> + <para> + Contains a null-terminated string that identifies the + bus. The name must be unique across the kdbus domain and + must start with the effective UID of the caller, followed by + a '<literal>-</literal>' (dash). This item is mandatory. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_BLOOM_PARAMETER</constant></term> + <listitem> + <para> + Bus-wide bloom parameters passed in a + <type>struct kdbus_bloom_parameter</type>. These settings are + copied back to new connections verbatim. This item is + mandatory. See + <citerefentry> + <refentrytitle>kdbus.item</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for a more detailed description of this item. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_ATTACH_FLAGS_SEND</constant></term> + <listitem> + <para> + An optional item that contains a set of attach flags that are + returned to connections when they query the bus creator + metadata. If not set, no metadata is returned. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_NEGOTIATE</constant></term> + <listitem><para> + With this item, programs can <emphasis>probe</emphasis> the + kernel for known item types. See + <citerefentry> + <refentrytitle>kdbus.item</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for more details. + </para></listitem> + </varlistentry> + </variablelist> + </listitem> + </varlistentry> + </variablelist> + + <para> + Unrecognized items are rejected, and the ioctl will fail with + <varname>errno</varname> set to <constant>EINVAL</constant>. + </para> + </refsect1> + + <refsect1> + <title>Return value</title> + <para> + On success, all mentioned ioctl commands return <errorcode>0</errorcode>; + on error, <errorcode>-1</errorcode> is returned, and + <varname>errno</varname> is set to indicate the error. + If the issued ioctl is illegal for the file descriptor used, + <varname>errno</varname> will be set to <constant>ENOTTY</constant>. + </para> + + <refsect2> + <title> + <constant>KDBUS_CMD_BUS_MAKE</constant> may fail with the following + errors + </title> + + <variablelist> + <varlistentry> + <term><constant>EBADMSG</constant></term> + <listitem><para> + A mandatory item is missing. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>EINVAL</constant></term> + <listitem><para> + The flags supplied in the <constant>struct kdbus_cmd</constant> + are invalid or the supplied name does not start with the current + UID and a '<literal>-</literal>' (dash). + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>EEXIST</constant></term> + <listitem><para> + A bus of that name already exists. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>ESHUTDOWN</constant></term> + <listitem><para> + The kdbus mount instance for the bus was already shut down. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>EMFILE</constant></term> + <listitem><para> + The maximum number of buses for the current user is exhausted. + </para></listitem> + </varlistentry> + </variablelist> + </refsect2> + </refsect1> + + <refsect1> + <title>See Also</title> + <simplelist type="inline"> + <member> + <citerefentry> + <refentrytitle>kdbus</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.connection</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.endpoint</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.fs</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.item</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.message</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.name</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.pool</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + </simplelist> + </refsect1> +</refentry> |