sd_bus_send, sd_bus_send_to, sd_bus_message_send — Queue a D-Bus message for transfer
#include <systemd/sd-bus.h>
int sd_bus_send( | sd_bus *bus, |
| sd_bus_message *m, | |
uint64_t *cookie); |
int sd_bus_send_to( | sd_bus *bus, |
| sd_bus_message *m, | |
| const char *destination, | |
uint64_t *cookie); |
int sd_bus_message_send( | sd_bus_message *m); |
sd_bus_send() queues the bus message object m for
transfer. If bus is NULL, the bus that
m is attached to is used. bus only needs to be set when the
message is sent to a different bus than the one it's attached to, for example when forwarding messages.
If the output parameter cookie is not NULL, it is set to the
message identifier. This value can later be used to match incoming replies to their corresponding
messages. If cookie is set to NULL and the message is not
sealed, sd_bus_send() assumes the message m doesn't expect a
reply and adds the necessary headers to indicate this.
Note that in most scenarios, sd_bus_send() should not be called
directly. Instead, use higher level functions such as
sd_bus_call_method(3) and
sd_bus_reply_method_return(3)
which call sd_bus_send() internally.
sd_bus_send_to() is a shorthand for sending a message to a specific
destination. It's main use case is to simplify sending unicast signal messages (signals that only have a
single receiver). It's behavior is similar to calling
sd_bus_message_set_destination(3)
followed by calling sd_bus_send().
sd_bus_send()/sd_bus_send_to() will write the message
directly to the underlying transport (e.g. kernel socket buffer) if possible. If the connection is not
set up fully yet the message is queued locally. If the transport buffers are congested any unwritten
message data is queued locally, too. If the connection has been closed or is currently being closed the
call fails.
sd_bus_process(3) should
be invoked to write out any queued message data to the transport.
sd_bus_message_send() is the same as sd_bus_send() but
without the first and last argument. sd_bus_message_send(m) is equivalent to
sd_bus_send(sd_bus_message_get_bus(m), m, NULL).
On success, these functions return a non-negative integer. On failure, they return a negative errno-style error code.
Returned errors may indicate the following problems:
-EINVAL¶The input parameter m is NULL.
-EOPNOTSUPP¶The bus connection does not support sending file descriptors.
-ECHILD¶The bus connection was allocated in a parent process and is being reused in a child
process after fork().
-ENOBUFS¶The bus connection's write queue is full.
-ENOTCONN¶The input parameter bus is
NULL or the bus is not connected.
-ECONNRESET¶The bus connection was closed while waiting for the response.
-ENOMEM¶Memory allocation failed.
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.