--- /dev/null
+<?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
+ "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
+
+<!--
+ This file is part of systemd.
+
+ Copyright 2010 Lennart Poettering
+
+ systemd is free software; you can redistribute it and/or modify it
+ under the terms of the GNU Lesser General Public License as published by
+ the Free Software Foundation; either version 2.1 of the License, or
+ (at your option) any later version.
+
+ systemd is distributed in the hope that it will be useful, but
+ WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public License
+ along with systemd; If not, see <http://www.gnu.org/licenses/>.
+-->
+
+<refentry id="sd_listen_fds"
+ xmlns:xi="http://www.w3.org/2001/XInclude">
+
+ <refentryinfo>
+ <title>sd_listen_fds</title>
+ <productname>systemd</productname>
+
+ <authorgroup>
+ <author>
+ <contrib>Developer</contrib>
+ <firstname>Lennart</firstname>
+ <surname>Poettering</surname>
+ <email>lennart@poettering.net</email>
+ </author>
+ </authorgroup>
+ </refentryinfo>
+
+ <refmeta>
+ <refentrytitle>sd_listen_fds</refentrytitle>
+ <manvolnum>3</manvolnum>
+ </refmeta>
+
+ <refnamediv>
+ <refname>sd_listen_fds</refname>
+ <refname>sd_listen_fds_with_names</refname>
+ <refname>SD_LISTEN_FDS_START</refname>
+ <refpurpose>Check for file descriptors passed by the system manager</refpurpose>
+ </refnamediv>
+
+ <refsynopsisdiv>
+ <funcsynopsis>
+ <funcsynopsisinfo>#include <systemd/sd-daemon.h></funcsynopsisinfo>
+
+ <funcsynopsisinfo>#define SD_LISTEN_FDS_START 3</funcsynopsisinfo>
+
+ <funcprototype>
+ <funcdef>int <function>sd_listen_fds</function></funcdef>
+ <paramdef>int <parameter>unset_environment</parameter></paramdef>
+ </funcprototype>
+
+ <funcprototype>
+ <funcdef>int <function>sd_listen_fds_with_names</function></funcdef>
+ <paramdef>int <parameter>unset_environment</parameter></paramdef>
+ <paramdef>char*** <parameter>names</parameter></paramdef>
+ </funcprototype>
+ </funcsynopsis>
+ </refsynopsisdiv>
+
+ <refsect1>
+ <title>Description</title>
+
+ <para><function>sd_listen_fds()</function> may be invoked by a
+ daemon to check for file descriptors passed by the service manager as
+ part of the socket-based activation logic. It returns the number
+ of received file descriptors. If no file descriptors have been
+ received, zero is returned. The first file descriptor may be found
+ at file descriptor number 3
+ (i.e. <constant>SD_LISTEN_FDS_START</constant>), the remaining
+ descriptors follow at 4, 5, 6, …, if any.</para>
+
+ <para>If a daemon receives more than one file descriptor, they
+ will be passed in the same order as configured in the systemd
+ socket unit file (see
+ <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+ for details). Nonetheless, it is recommended to verify the correct
+ socket types before using them. To simplify this checking, the
+ functions
+ <citerefentry><refentrytitle>sd_is_fifo</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd_is_socket</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd_is_socket_inet</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd_is_socket_unix</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ are provided. In order to maximize flexibility, it is recommended
+ to make these checks as loose as possible without allowing
+ incorrect setups. i.e. often, the actual port number a socket is
+ bound to matters little for the service to work, hence it should
+ not be verified. On the other hand, whether a socket is a datagram
+ or stream socket matters a lot for the most common program logics
+ and should be checked.</para>
+
+ <para>This function call will set the FD_CLOEXEC flag for all
+ passed file descriptors to avoid further inheritance to children
+ of the calling process.</para>
+
+ <para>If multiple socket units activate the same service, the order
+ of the file descriptors passed to its main process is undefined.
+ If additional file descriptors have been passed to the service
+ manager using
+ <citerefentry><refentrytitle>sd_pid_notify_with_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>'s
+ <literal>FDSTORE=1</literal> messages, these file descriptors are
+ passed last, in arbitrary order, and with duplicates
+ removed.</para>
+
+ <para>If the <parameter>unset_environment</parameter> parameter is
+ non-zero, <function>sd_listen_fds()</function> will unset the
+ <varname>$LISTEN_FDS</varname>, <varname>$LISTEN_PID</varname> and
+ <varname>$LISTEN_FDNAMES</varname> environment variables before
+ returning (regardless of whether the function call itself
+ succeeded or not). Further calls to
+ <function>sd_listen_fds()</function> will then return zero, but the
+ variables are no longer inherited by child processes.</para>
+
+ <para><function>sd_listen_fds_with_names()</function> is like
+ <function>sd_listen_fds()</function>, but optionally also returns
+ an array of strings with identification names for the passed file
+ descriptors, if that is available and the
+ <parameter>names</parameter> parameter is non-NULL. This
+ information is read from the <varname>$LISTEN_FDNAMES</varname>
+ variable, which may contain a colon-separated list of names. For
+ socket-activated services, these names may be configured with the
+ <varname>FileDescriptorName=</varname> setting in socket unit
+ files, see
+ <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+ for details. For file descriptors pushed into the file descriptor
+ store (see above), the name is set via the
+ <varname>FDNAME=</varname> field transmitted via
+ <function>sd_pid_notify_with_fds()</function>. The primary usecase
+ for these names are services which accept a variety of file
+ descriptors which are not recognizable with functions like
+ <function>sd_is_socket()</function> alone, and thus require
+ identification via a name. It is recommended to rely on named file
+ descriptors only if identification via
+ <function>sd_is_socket()</function> and related calls is not
+ sufficient. Note that the names used are not unique in any
+ way. The returned array of strings has as many entries as file
+ descriptors have been received, plus a final NULL pointer
+ terminating the array. The caller needs to free the array itself
+ and each of its elements with libc's <function>free()</function>
+ call after use. If the <parameter>names</parameter> parameter is
+ NULL, the call is entirely equivalent to
+ <function>sd_listen_fds()</function>.</para>
+
+ <para>Under specific conditions, the following automatic file
+ descriptor names are returned:
+
+ <table>
+ <title>
+ <command>Special names</command>
+ </title>
+
+ <tgroup cols='2'>
+ <thead>
+ <row>
+ <entry>Name</entry>
+ <entry>Description</entry>
+ </row>
+ </thead>
+ <tbody>
+ <row>
+ <entry><literal>unknown</literal></entry>
+ <entry>The process received no name for the specific file descriptor from the service manager.</entry>
+ </row>
+
+ <row>
+ <entry><literal>stored</literal></entry>
+ <entry>The file descriptor originates in the service manager's per-service file descriptor store, and the <varname>FDNAME=</varname> field was absent when the file descriptor was submitted to the service manager.</entry>
+ </row>
+
+ <row>
+ <entry><literal>connection</literal></entry>
+ <entry>The service was activated in per-connection style using <varname>Accept=yes</varname> in the socket unit file, and the file descriptor is the connection socket.</entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </table>
+ </para>
+ </refsect1>
+
+ <refsect1>
+ <title>Return Value</title>
+
+ <para>On failure, these calls returns a negative errno-style error
+ code. If
+ <varname>$LISTEN_FDS</varname>/<varname>$LISTEN_PID</varname> was
+ not set or was not correctly set for this daemon and hence no file
+ descriptors were received, 0 is returned. Otherwise, the number of
+ file descriptors passed is returned. The application may find them
+ starting with file descriptor SD_LISTEN_FDS_START, i.e. file
+ descriptor 3.</para>
+ </refsect1>
+
+ <refsect1>
+ <title>Notes</title>
+
+ <xi:include href="libelogind-pkgconfig.xml" xpointer="pkgconfig-text"/>
+
+ <para>Internally, <function>sd_listen_fds()</function> checks
+ whether the <varname>$LISTEN_PID</varname> environment variable
+ equals the daemon PID. If not, it returns immediately. Otherwise,
+ it parses the number passed in the <varname>$LISTEN_FDS</varname>
+ environment variable, then sets the FD_CLOEXEC flag for the parsed
+ number of file descriptors starting from SD_LISTEN_FDS_START.
+ Finally, it returns the parsed
+ number. <function>sd_listen_fds_with_names()</function> does the
+ same but also parses <varname>$LISTEN_FDNAMES</varname> if
+ set.</para>
+ </refsect1>
+
+ <refsect1>
+ <title>Environment</title>
+
+ <variablelist class='environment-variables'>
+ <varlistentry>
+ <term><varname>$LISTEN_PID</varname></term>
+ <term><varname>$LISTEN_FDS</varname></term>
+ <term><varname>$LISTEN_FDNAMES</varname></term>
+
+ <listitem><para>Set by the service manager for supervised
+ processes that use socket-based activation. This environment
+ variable specifies the data
+ <function>sd_listen_fds()</function> and
+ <function>sd_listen_fds_with_names()</function> parses. See
+ above for details.</para></listitem>
+ </varlistentry>
+ </variablelist>
+ </refsect1>
+
+ <refsect1>
+ <title>See Also</title>
+
+ <para>
+ <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd_is_fifo</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd_is_socket</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd_is_socket_inet</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd_is_socket_unix</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd_pid_notify_with_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+ </para>
+ </refsect1>
+
+</refentry>
~ianmdlvl / elogind.git / blobdiff