x SuSE Linux 13.1-RELEASE x
x SuSE Linux 13.1-RELEASEx
SD_EVENT_ADD_IO(3) sd_event_add_io SD_EVENT_ADD_IO(3)
NAME
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_get_io_fd_own, sd_event_source_set_io_fd_own,
sd_event_source, sd_event_io_handler_t - Add an I/O event source to an
event loop
SYNOPSIS
#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);
int sd_event_source_get_io_fd_own(sd_event_source *source);
int sd_event_source_set_io_fd_own(sd_event_source *source, int b);
DESCRIPTION
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 is a function to call when the event source is triggered or
NULL. 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. The handler may return
negative to signal an error (see below), other return values are
ignored. If handler is NULL, a default handler that calls
sd_event_exit(3) will be used.
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 either be disabled after the invocation,
even if the SD_EVENT_ON mode was requested before, or it will cause the
loop to terminate, see sd_event_source_set_exit_on_failure(3). 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 seen.
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
instead.
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
SD_EVENT_OFF.
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.
If the handler to sd_event_add_io() is NULL, and the event source
fires, this will be considered a request to exit the event loop. In
this case, the userdata parameter, cast to an integer, is passed as the
exit code parameter to sd_event_exit(3).
Note that this call does not take possession of the file descriptor
passed in, ownership (and thus the duty to close it when it is no
longer needed) remains with the caller. However, with the
sd_event_source_set_io_fd_own() call (see below) the event source may
optionally take ownership of the file descriptor after the event source
has been created. In that case the file descriptor is closed
automatically as soon as the event source is released.
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. If the event source
takes the ownership of the previous file descriptor, that is,
sd_event_source_set_io_fd_own() was called for the event source with a
non-zero value, then the previous file descriptor will be closed and
the event source will also take the ownership of the new file
descriptor on success.
sd_event_source_set_io_fd_own() controls whether the file descriptor of
the event source shall be closed automatically when the event source is
freed (or when the file descriptor assigned to the event source is
replaced by sd_event_source_set_io_fd()), i.e. whether it shall be
considered 'owned' by the event source object. By default it is not
closed automatically, and the application has to do this on its own.
The b parameter is a boolean parameter: if zero, the file descriptor is
not closed automatically when the event source is freed, otherwise it
is closed.
sd_event_source_get_io_fd_own() may be used to query the current
setting of the file descriptor ownership boolean flag as set with
sd_event_source_set_io_fd_own(). It returns positive if the file
descriptor is closed automatically when the event source is destroyed,
zero if not, and negative on error.
RETURN VALUE
On success, these functions return 0 or a positive integer. On failure,
they return a negative errno-style error code.
Errors
Returned values may indicate the following problems:
-ENOMEM
Not enough memory to allocate an object.
-EINVAL
An invalid argument has been passed.
-ESTALE
The event loop is already terminated.
-ECHILD
The event loop has been created in a different process, library or
module instance.
-EDOM
The passed event source is not an I/O event source.
NOTES
Functions described here are available as a shared library, which can
be compiled against and linked to with the libsystemd pkg-config(1)
file.
The code described here uses getenv(3), which is declared to be not
multi-thread-safe. This means that the code calling the functions
described here must not call setenv(3) from a parallel thread. It is
recommended to only do calls to setenv() from an early phase of the
program when no other threads have been started.
SEE ALSO
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_inotify(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), sd_event_source_set_floating(3),
epoll_ctl(2), epoll(7)
systemd 254 SD_EVENT_ADD_IO(3)
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