sd_is_fifo, sd_is_socket, sd_is_socket_inet, sd_is_socket_unix, sd_is_mq — Check the type of a file descriptor
#include <systemd/sd-daemon.h>
| int sd_is_fifo( | int fd, | 
| const char *path ); | 
| int sd_is_socket( | int fd, | 
| int family, | |
| int type, | |
| int listening ); | 
| int sd_is_socket_inet( | int fd, | 
| int family, | |
| int type, | |
| int listening, | |
| uint16_t port ); | 
| int sd_is_socket_unix( | int fd, | 
| int type, | |
| int listening, | |
| const char* path, | |
| size_t length ); | 
| int sd_is_mq( | int fd, | 
| const char *path ); | 
sd_is_fifo() may be called
                to check whether the specified file descriptor refers
                to a FIFO or pipe. If the path
                parameter is not NULL, it is checked whether the FIFO
                is bound to the specified file system path.
sd_is_socket() may be
                called to check whether the specified file descriptor
                refers to a socket. If the
                family parameter is not
                AF_UNSPEC it is checked whether the socket is of the
                specified family (AF_UNIX, AF_INET, ...). If the
                type parameter is not 0 it is
                checked whether the socket is of the specified type
                (SOCK_STREAM, SOCK_DGRAM, ...). If the
                listening parameter is positive
                it is checked whether the socket is in accepting mode,
                i.e. listen() has been called for
                it. If listening is 0, it is
                checked whether the socket is not in this mode. If the
                parameter is negative, no such check is made. The
                listening parameter should only
                be used for stream sockets and should be set to a
                negative value otherwise.
sd_is_socket_inet() is
                similar to sd_is_socket(), but
                optionally checks the IPv4 or IPv6 port number the
                socket is bound to, unless port
                is zero. For this call family
                must be passed as either AF_UNSPEC, AF_INET, or
                AF_INET6.
sd_is_socket_unix() is
                similar to sd_is_socket(), but
                optionally checks the AF_UNIX path the socket is bound
                to, unless the path parameter
                is NULL. For normal file system AF_UNIX sockets set
                the length parameter to 0. For
                Linux abstract namespace sockets set the
                length to the size of the
                address, including the initial 0 byte and set
                path to the initial 0 byte of
                the socket address.
sd_is_mq() may be called to
                check whether the specified file descriptor refers to
                a POSIX message queue. If the
                path parameter is not NULL, it
                is checked whether the message queue is bound to the
                specified name.
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.
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.
Internally, these function use a combination of
                fstat() and
                getsockname() to check the file
                descriptor type and where it is bound to.
For details about the algorithms check the liberally licensed reference implementation sources: http://cgit.freedesktop.org/systemd/systemd/plain/src/libsystemd-daemon/sd-daemon.c and http://cgit.freedesktop.org/systemd/systemd/plain/src/systemd/sd-daemon.h
sd_is_fifo() and the
                related functions are implemented in the reference
                implementation's sd-daemon.c and
                sd-daemon.h files. These
                interfaces are available as shared library, which can
                be compiled and linked to with the
                libsystemd-daemon
                pkg-config(1)
                file. Alternatively, applications consuming these APIs
                may copy the implementation into their source
                tree. For more details about the reference
                implementation see
                sd-daemon(3).
These functions continue to work as described, even if -DDISABLE_SYSTEMD is set during compilation.