вызвать вызов метода D-Bus (Invoke a D-Bus method call)
Имя (Name)
sd_bus_call, sd_bus_call_async - Invoke a D-Bus method call
Синопсис (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);
Описание (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).
Возвращаемое значение (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.
Примечание (Note)
These APIs are implemented as a shared library, which can be
compiled and linked to with the libsystemd pkg-config(1) file.
Смотри также (See also)
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)
