sd_is_fifo

Index · Directives · Python · libudev · gudev systemd 204

## Name

sd_is_fifo, sd_is_socket, sd_is_socket_inet, sd_is_socket_unix, sd_is_mq — Check the type of a file descriptor

## Synopsis

    #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`)`;

## Description

`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.

## Return Value

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.

## Notes

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.

## See Also

systemd(1), sd-daemon(3), sd_listen_fds(3), systemd.service(5), systemd.socket(5)