systemd/man/sd_is_fifo.xml

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<refentry id="sd_is_fifo">

        <refentryinfo>
                <title>sd_is_fifo</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_is_fifo</refentrytitle>
                <manvolnum>3</manvolnum>
        </refmeta>

        <refnamediv>
                <refname>sd_is_fifo</refname>
                <refname>sd_is_socket</refname>
                <refname>sd_is_socket_inet</refname>
                <refname>sd_is_socket_unix</refname>
                <refname>sd_is_mq</refname>
                <refpurpose>Check the type of a file descriptor</refpurpose>
        </refnamediv>

        <refsynopsisdiv>
                <funcsynopsis>
                        <funcsynopsisinfo>#include &lt;systemd/sd-daemon.h&gt;</funcsynopsisinfo>

                        <funcprototype>
                                <funcdef>int <function>sd_is_fifo</function></funcdef>
                                <paramdef>int <parameter>fd</parameter></paramdef>
                                <paramdef>const char *<parameter>path</parameter></paramdef>
                        </funcprototype>

                        <funcprototype>
                                <funcdef>int <function>sd_is_socket</function></funcdef>
                                <paramdef>int <parameter>fd</parameter></paramdef>
                                <paramdef>int <parameter>family</parameter></paramdef>
                                <paramdef>int <parameter>type</parameter></paramdef>
                                <paramdef>int <parameter>listening</parameter></paramdef>
                        </funcprototype>

                        <funcprototype>
                                <funcdef>int <function>sd_is_socket_inet</function></funcdef>
                                <paramdef>int <parameter>fd</parameter></paramdef>
                                <paramdef>int <parameter>family</parameter></paramdef>
                                <paramdef>int <parameter>type</parameter></paramdef>
                                <paramdef>int <parameter>listening</parameter></paramdef>
                                <paramdef>uint16_t <parameter>port</parameter></paramdef>
                        </funcprototype>

                        <funcprototype>
                                <funcdef>int <function>sd_is_socket_unix</function></funcdef>
                                <paramdef>int <parameter>fd</parameter></paramdef>
                                <paramdef>int <parameter>type</parameter></paramdef>
                                <paramdef>int <parameter>listening</parameter></paramdef>
                                <paramdef>const char* <parameter>path</parameter></paramdef>
                                <paramdef>size_t <parameter>length</parameter></paramdef>
                        </funcprototype>

                        <funcprototype>
                                <funcdef>int <function>sd_is_mq</function></funcdef>
                                <paramdef>int <parameter>fd</parameter></paramdef>
                                <paramdef>const char *<parameter>path</parameter></paramdef>
                        </funcprototype>

                </funcsynopsis>
        </refsynopsisdiv>

        <refsect1>
                <title>Description</title>

                <para><function>sd_is_fifo()</function> may be called
                to check whether the specified file descriptor refers
                to a FIFO or pipe. If the <parameter>path</parameter>
                parameter is not NULL, it is checked whether the FIFO
                is bound to the specified file system path.</para>

                <para><function>sd_is_socket()</function> may be
                called to check whether the specified file descriptor
                refers to a socket. It the
                <parameter>family</parameter> parameter is not
                AF_UNSPEC it is checked whether the socket is of the
                specified family (AF_UNIX, AF_INET, ...). If the
                <parameter>type</parameter> parameter is not 0 it is
                checked whether the socket is of the specified type
                (SOCK_STREAM, SOCK_DGRAM, ...). If the
                <parameter>listening</parameter> parameter is positive
                it is checked whether the socket is in accepting mode,
                i.e. <function>listen()</function> has been called for
                it. If <parameter>listening</parameter> is 0, it is
                checked whether the socket is not in this mode. If the
                parameter is negative, no such check is made. The
                <parameter>listening</parameter> parameter should only
                be used for stream sockets and should be set to a
                negative value otherwise.</para>

                <para><function>sd_is_socket_inet()</function> is
                similar to <function>sd_is_socket()</function>, but
                optionally checks the IPv4 or IPv6 port number the
                socket is bound to, unless <parameter>port</parameter>
                is zero. For this call <parameter>family</parameter>
                must be passed as either AF_UNSPEC, AF_INET or
                AF_INET6.</para>

                <para><function>sd_is_socket_unix()</function> is
                similar to <function>sd_is_socket()</function>, but
                optionally checks the AF_UNIX path the socket is bound
                to, unless the <parameter>path</parameter> parameter
                is NULL. For normal file system AF_UNIX sockets set
                the <parameter>length</parameter> parameter to 0. For
                Linux abstract namespace sockets set the
                <parameter>length</parameter> to the size of the
                address, including the initial 0 byte and set
                <parameter>path</parameter> to the initial 0 byte of
                the socket address.</para>

                <para><function>sd_is_mq()</function> may be called to
                check whether the specified file descriptor refers to
                a POSIX message queue. If the
                <parameter>path</parameter> parameter is not NULL, it
                is checked whether the message queue is bound to the
                specified name.</para>
        </refsect1>

        <refsect1>
                <title>Return Value</title>

                <para>On failure, these calls return a negative
                errno-style error code. If the file descriptor is of
                the specified type and bound to the specified address
                a positive return value is returned, otherwise
                zero.</para>
        </refsect1>

        <refsect1>
                <title>Notes</title>

                <para>These functions are provided by the reference
                implementation of APIs for new-style daemons and
                distributed with the systemd package. The algorithms
                they implement are simple, and can easily be
                reimplemented in daemons if it is important to support
                this interface without using the reference
                implementation.</para>

                <para>Internally, these function use a combination of
                <filename>fstat()</filename> and
                <filename>getsockname()</filename> to check the file
                descriptor type and where it is bound to.</para>

                <para>For details about the algorithms check the
                liberally licensed reference implementation sources:
                <ulink url="http://cgit.freedesktop.org/systemd/systemd/plain/src/sd-daemon.c"/>
                resp. <ulink
                url="http://cgit.freedesktop.org/systemd/systemd/plain/src/systemd/sd-daemon.h"/></para>

                <para><function>sd_is_fifo()</function> and the
                related functions are implemented in the reference
                implementation's <filename>sd-daemon.c</filename> and
                <filename>sd-daemon.h</filename> files. These
                interfaces are available as shared library, which can
                be compiled and linked to with the
                <literal>libsystemd-daemon</literal>
                <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
                file. Alternatively, applications consuming these APIs
                may copy the implementation into their source
                tree. For more details about the reference
                implementation see
                <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>

                <para>These functions continue to work as described,
                even if -DDISABLE_SYSTEMD is set during
                compilation.</para>
        </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_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>
                </para>
        </refsect1>

</refentry>