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Diffstat (limited to 'src/libsystemd/sd_listen_fds.xml')
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diff --git a/src/libsystemd/sd_listen_fds.xml b/src/libsystemd/sd_listen_fds.xml new file mode 100644 index 0000000000..93bf8d853f --- /dev/null +++ b/src/libsystemd/sd_listen_fds.xml @@ -0,0 +1,257 @@ +<?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="libsystemd-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> |