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| Copyright 2010 Lennart Poettering |
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| |
| <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> |