Ubuntu Manpage: sd_bus_call, sd_bus_call_async

Provided by: libsystemd-dev_257.4-1ubuntu3.2_amd64

NAME

       sd_bus_call, sd_bus_call_async - Invoke a D-Bus method call

SYNOPSIS

       #include <systemd/sd-bus.h>

       typedef int (*sd_bus_message_handler_t)(sd_bus_message *m, void *userdata, sd_bus_error *ret_error);

       int sd_bus_call(sd_bus *bus, sd_bus_message *m, uint64_t usec, sd_bus_error *ret_error,
                       sd_bus_message **reply);

       int sd_bus_call_async(sd_bus *bus, sd_bus_slot **slot, sd_bus_message *m,
                             sd_bus_message_handler_t callback, void *userdata, uint64_t usec);

DESCRIPTION

sd_bus_call() takes a complete bus message object and calls the corresponding D-Bus method. On success,
the response is stored in reply. usec indicates the timeout in microseconds. If ret_error is not NULL
and sd_bus_call() fails (either because of an internal error or because it received a D-Bus error reply),
ret_error is initialized to an instance of sd_bus_error describing the error.

sd_bus_call_async() is like sd_bus_call() but works asynchronously. The callback indicates the function
to call when the response arrives. The userdata pointer will be passed to the callback function, and may
be chosen freely by the caller. If slot is not NULL and sd_bus_call_async() succeeds, slot is set to a
slot object which can be used to cancel the method call at a later time using sd_bus_slot_unref(3). If
slot is NULL, the lifetime of the method call is bound to the lifetime of the bus object itself, and it
cannot be cancelled independently. See sd_bus_slot_set_floating(3) for details. callback is called when
a reply arrives with the reply, userdata and an sd_bus_error output parameter as its arguments. Unlike
sd_bus_call(), the sd_bus_error output parameter passed to the callback will be empty. To determine
whether the method call succeeded, use sd_bus_message_is_method_error(3) on the reply message passed to
the callback instead. If the callback returns zero and the sd_bus_error output parameter is still empty
when the callback finishes, other handlers registered with functions such as sd_bus_add_filter(3) or
sd_bus_add_match(3) are given a chance to process the message. If the callback returns a non-zero value
or the sd_bus_error output parameter is not empty when the callback finishes, no further processing of
the message is done. Generally, you want to return zero from the callback to give other registered
handlers a chance to process the reply as well. (Note that the sd_bus_error parameter is an output
parameter of the callback function, not an input parameter; it can be used to propagate errors from the
callback handler, it will not receive any error that was received as method reply.)

The message m passed to the callback is only borrowed, that is, the callback should not call
sd_bus_message_unref(3) on it. If the callback wants to hold on to the message beyond the lifetime of the
callback, it needs to call sd_bus_message_ref(3) to create a new reference.

If usec is zero, the default D-Bus method call timeout is used. See sd_bus_get_method_call_timeout(3).

RETURN VALUE

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

   Errors
       When sd_bus_call() internally receives a D-Bus error reply, it will set ret_error if it is not NULL, and
       will return a negative value mapped from the error reply, see sd_bus_error_get_errno(3).

       Returned errors may indicate the following problems:

       -EINVAL
           The input parameter m is NULL.

           The input parameter m is not a D-Bus method call. To create a new D-Bus method call, use
           sd_bus_message_new_method_call(3).

           The input parameter m has the BUS_MESSAGE_NO_REPLY_EXPECTED flag set.

           The input parameter error is non-NULL but was not set to SD_BUS_ERROR_NULL.

       -ECHILD
           The bus connection was allocated in a parent process and is being reused in a child process after
           fork().

       -ENOTCONN
           The input parameter bus is NULL or the bus is not connected.

       -ECONNRESET
           The bus connection was closed while waiting for the response.

       -ETIMEDOUT
           A response was not received within the given timeout.

       -ELOOP
           The message m is addressed to its own client.

       -ENOMEM
           Memory allocation failed.

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.

HISTORY