sd_bus_send - Man Page

Queue a D-Bus message for transfer

Synopsis

#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);

Description

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.

Return Value

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

Errors

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.

Notes

These APIs are implemented as a shared library, which can be compiled and linked to with the libsystemd pkg-config(1) file.

See Also

systemd(1), sd-bus(3), sd_bus_call_method(3), sd_bus_message_set_destination(3), sd_bus_reply_method_return(3), sd_bus_process(3)

Referenced By

sd-bus(3), sd_bus_default(3), sd_bus_emit_signal(3), sd_bus_enqueue_for_read(3), sd_bus_get_n_queued_read(3), sd_bus_message_seal(3), sd_bus_set_watch_bind(3), sd_bus_start(3), systemd.directives(7), systemd.index(7).

The man page sd_bus_send_to(3) is an alias of sd_bus_send(3).

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