sd_bus_call

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¶

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