SD_EVENT_ADD_IO(3)             sd_event_add_io            SD_EVENT_ADD_IO(3)

NAME         top

       sd_event_add_io, sd_event_source_get_io_events,
       sd_event_source_set_io_events, sd_event_source_get_io_revents,
       sd_event_source_get_io_fd, sd_event_source_set_io_fd,
       sd_event_source, sd_event_io_handler_t - Add an I/O event source to
       an event loop

SYNOPSIS         top

       #include <systemd/sd-event.h>

       typedef struct sd_event_source sd_event_source;

       typedef int (*sd_event_io_handler_t)(sd_event_source *s, int fd,
                                            uint32_t revents,
                                            void *userdata);

       int sd_event_add_io(sd_event *event, sd_event_source **source,
                           int fd, uint32_t events,
                           sd_event_io_handler_t handler, void *userdata);

       int sd_event_source_get_io_events(sd_event_source *source,
                                         uint32_t *events);

       int sd_event_source_set_io_events(sd_event_source *source,
                                         uint32_t events);

       int sd_event_source_get_io_revents(sd_event_source *source,
                                          uint32_t *revents);

       int sd_event_source_get_io_fd(sd_event_source *source);

       int sd_event_source_set_io_fd(sd_event_source *source, int fd);

DESCRIPTION         top

       sd_event_add_io() adds a new I/O event source to an event loop. The
       event loop object is specified in the event parameter, the event
       source object is returned in the source parameter. The fd parameter
       takes the UNIX file descriptor to watch, which may refer to a socket,
       a FIFO, a message queue, a serial connection, a character device, or
       any other file descriptor compatible with Linux epoll(7). The events
       parameter takes a bit mask of events to watch for, a combination of
       the following event flags: EPOLLIN, EPOLLOUT, EPOLLRDHUP, EPOLLPRI,
       and EPOLLET, see epoll_ctl(2) for details. The handler shall
       reference a function to call when the event source is triggered. The
       userdata pointer will be passed to the handler function, and may be
       chosen freely by the caller. The handler will also be passed the file
       descriptor the event was seen on, as well as the actual event flags.
       It's generally a subset of the events watched, however may
       additionally include EPOLLERR and EPOLLHUP.

       By default, an event source will stay enabled continuously
       (SD_EVENT_ON), but this may be changed with
       sd_event_source_set_enabled(3). If the handler function returns a
       negative error code, it will be disabled after the invocation, even
       if the SD_EVENT_ON mode was requested before. Note that an event
       source set to SD_EVENT_ON will fire continuously unless data is read
       from or written to the file descriptor to reset the mask of events

       Setting the I/O event mask to watch for to 0 does not mean that the
       event source won't be triggered anymore, as EPOLLHUP and EPOLLERR may
       be triggered even with a zero event mask. To temporarily disable an
       I/O event source use sd_event_source_set_enabled(3) with SD_EVENT_OFF

       To destroy an event source object use sd_event_source_unref(3), but
       note that the event source is only removed from the event loop when
       all references to the event source are dropped. To make sure an event
       source does not fire anymore, even if it is still referenced, disable
       the event source using sd_event_source_set_enabled(3) with

       If the second parameter of sd_event_add_io() is NULL no reference to
       the event source object is returned. In this case the event source is
       considered "floating", and will be destroyed implicitly when the
       event loop itself is destroyed.

       It is recommended to use sd_event_add_io() only in conjunction with
       file descriptors that have O_NONBLOCK set, to ensure that all I/O
       operations from invoked handlers are properly asynchronous and
       non-blocking. Using file descriptors without O_NONBLOCK might result
       in unexpected starvation of other event sources. See fcntl(2) for
       details on enabling O_NONBLOCK mode.

       sd_event_source_get_io_events() retrieves the configured mask of
       watched I/O events of an event source created previously with
       sd_event_add_io(). It takes the event source object and a pointer to
       a variable to store the mask in.

       sd_event_source_set_io_events() configures the mask of watched I/O
       events of an event source created previously with sd_event_add_io().
       It takes the event source object and the new event mask.

       sd_event_source_get_io_revents() retrieves the I/O event mask of
       currently seen but undispatched events from an event source created
       previously with sd_event_add_io(). It takes the event source object
       and a pointer to a variable to store the event mask in. When called
       from a handler function on the handler's event source object this
       will return the same mask as passed to the handler's revents
       parameter. This call is primarily useful to check for undispatched
       events of an event source from the handler of an unrelated (possibly
       higher priority) event source. Note the relation between
       sd_event_source_get_pending() and sd_event_source_get_io_revents():
       both functions will report non-zero results when there's an event
       pending for the event source, but the former applies to all event
       source types, the latter only to I/O event sources.

       sd_event_source_get_io_fd() retrieves the UNIX file descriptor of an
       event source created previously with sd_event_add_io(). It takes the
       event source object and returns the non-negative file descriptor or a
       negative error number on error (see below).

       sd_event_source_set_io_fd() changes the UNIX file descriptor of an
       I/O event source created previously with sd_event_add_io(). It takes
       the event source object and the new file descriptor.

RETURN VALUE         top

       On success, these functions return 0 or a positive integer. On
       failure, they return a negative errno-style error code.

ERRORS         top

       Returned values may indicate the following problems:

           Not enough memory to allocate an object.

           An invalid argument has been passed.

           The event loop is already terminated.

           The event loop has been created in a different process.

           The passed event source is not an I/O event source.

NOTES         top

       These APIs are implemented as a shared library, which can be compiled
       and linked to with the libsystemd pkg-config(1) file.

SEE ALSO         top

       systemd(1), sd-event(3), sd_event_new(3), sd_event_now(3),
       sd_event_add_time(3), sd_event_add_signal(3), sd_event_add_child(3),
       sd_event_add_defer(3), sd_event_source_set_enabled(3),
       sd_event_source_set_priority(3), sd_event_source_set_userdata(3),
       sd_event_source_set_description(3), sd_event_source_get_pending(3),
       epoll_ctl(3), epoll(7)

COLOPHON         top

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systemd 233                                               SD_EVENT_ADD_IO(3)