Ubuntu Manpage: sd_bus_call, sd_bus_call_async

Provided by: libsystemd-dev_255.4-1ubuntu8.4_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.

           Added in version 246.  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().

           Added in version 246.

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

           Added in version 246.

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

           Added in version 246.

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

           Added in version 246.

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

           Added in version 246.

       -ENOMEM
           Memory allocation failed.

           Added in version 246.

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