sd_bus_call(3) — Linux manual page


SD_BUS_CALL(3)                 sd_bus_call                SD_BUS_CALL(3)

NAME         top

       sd_bus_call, sd_bus_call_async - Invoke a D-Bus method call

SYNOPSIS         top

       #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         top

       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         top

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

       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:

           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

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

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

           The bus connection was closed while waiting for the response.

           A response was not received within the given timeout.

           The message m is addressed to its own client.

           Memory allocation failed.

NOTES         top

       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

HISTORY         top

       sd_bus_call() and sd_bus_call_async() were added in version 221.

SEE ALSO         top

       systemd(1), sd-bus(3), sd_bus_call_method(3),
       sd_bus_call_method_async(3), sd_bus_message_new_method_call(3),
       sd_bus_message_append(3), sd_bus_error(3)

COLOPHON         top

       This page is part of the systemd (systemd system and service
       manager) project.  Information about the project can be found at
       ⟨⟩.  If you have
       a bug report for this manual page, see
       This page was obtained from the project's upstream Git repository
       ⟨⟩ on 2024-06-14.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2024-06-13.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to

systemd 257~devel                                         SD_BUS_CALL(3)

Pages that refer to this page: sd-bus(3)sd_bus_call_method(3)sd_bus_message_new_method_call(3)sd_bus_message_seal(3)sd_bus_pending_method_calls(3)sd_bus_set_method_call_timeout(3)sd_bus_set_watch_bind(3)sd_bus_slot_set_userdata(3)sd_bus_start(3)systemd.directives(7)systemd.index(7)