'\" t
.TH "SD_BUS_CALL" "3" "" "systemd 256.7" "sd_bus_call"
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.SH "NAME"
sd_bus_call, sd_bus_call_async \- Invoke a D\-Bus method call
.SH "SYNOPSIS"
.sp
.ft B
.nf
#include <systemd/sd\-bus\&.h>
.fi
.ft
.HP \w'typedef\ int\ (*sd_bus_message_handler_t)('u
.BI "typedef int (*sd_bus_message_handler_t)(sd_bus_message\ *" "m" ", void\ *" "userdata" ", sd_bus_error\ *" "ret_error" ");"
.HP \w'int\ sd_bus_call('u
.BI "int sd_bus_call(sd_bus\ *" "bus" ", sd_bus_message\ *" "m" ", uint64_t\ " "usec" ", sd_bus_error\ *" "ret_error" ", sd_bus_message\ **" "reply" ");"
.HP \w'int\ sd_bus_call_async('u
.BI "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" ");"
.SH "DESCRIPTION"
.PP
\fBsd_bus_call()\fR
takes a complete bus message object and calls the corresponding D\-Bus method\&. On success, the response is stored in
\fIreply\fR\&.
\fIusec\fR
indicates the timeout in microseconds\&. If
\fIret_error\fR
is not
\fBNULL\fR
and
\fBsd_bus_call()\fR
fails (either because of an internal error or because it received a D\-Bus error reply),
\fIret_error\fR
is initialized to an instance of
sd_bus_error
describing the error\&.
.PP
\fBsd_bus_call_async()\fR
is like
\fBsd_bus_call()\fR
but works asynchronously\&. The
\fIcallback\fR
indicates the function to call when the response arrives\&. The
\fIuserdata\fR
pointer will be passed to the callback function, and may be chosen freely by the caller\&. If
\fIslot\fR
is not
\fBNULL\fR
and
\fBsd_bus_call_async()\fR
succeeds,
\fIslot\fR
is set to a slot object which can be used to cancel the method call at a later time using
\fBsd_bus_slot_unref\fR(3)\&. If
\fIslot\fR
is
\fBNULL\fR, the lifetime of the method call is bound to the lifetime of the bus object itself, and it cannot be cancelled independently\&. See
\fBsd_bus_slot_set_floating\fR(3)
for details\&.
\fIcallback\fR
is called when a reply arrives with the reply,
\fIuserdata\fR
and an
sd_bus_error
output parameter as its arguments\&. Unlike
\fBsd_bus_call()\fR, the
sd_bus_error
output parameter passed to the callback will be empty\&. To determine whether the method call succeeded, use
\fBsd_bus_message_is_method_error\fR(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
\fBsd_bus_add_filter\fR(3)
or
\fBsd_bus_add_match\fR(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\&.)
.PP
The message
\fIm\fR
passed to the callback is only borrowed, that is, the callback should not call
\fBsd_bus_message_unref\fR(3)
on it\&. If the callback wants to hold on to the message beyond the lifetime of the callback, it needs to call
\fBsd_bus_message_ref\fR(3)
to create a new reference\&.
.PP
If
\fIusec\fR
is zero, the default D\-Bus method call timeout is used\&. See
\fBsd_bus_get_method_call_timeout\fR(3)\&.
.SH "RETURN VALUE"
.PP
On success, these functions return a non\-negative integer\&. On failure, they return a negative errno\-style error code\&.
.SS "Errors"
.PP
When
\fBsd_bus_call()\fR
internally receives a D\-Bus error reply, it will set
\fIret_error\fR
if it is not
\fBNULL\fR, and will return a negative value mapped from the error reply, see
\fBsd_bus_error_get_errno\fR(3)\&.
.PP
Returned errors may indicate the following problems:
.PP
\fB\-EINVAL\fR
.RS 4
The input parameter
\fIm\fR
is
\fBNULL\fR\&.
.sp
The input parameter
\fIm\fR
is not a D\-Bus method call\&. To create a new D\-Bus method call, use
\fBsd_bus_message_new_method_call\fR(3)\&.
.sp
The input parameter
\fIm\fR
has the
\fBBUS_MESSAGE_NO_REPLY_EXPECTED\fR
flag set\&.
.sp
The input parameter
\fIerror\fR
is non\-\fBNULL\fR
but was not set to
\fBSD_BUS_ERROR_NULL\fR\&.
.RE
.PP
\fB\-ECHILD\fR
.RS 4
The bus connection was allocated in a parent process and is being reused in a child process after
\fBfork()\fR\&.
.RE
.PP
\fB\-ENOTCONN\fR
.RS 4
The input parameter
\fIbus\fR
is
\fBNULL\fR
or the bus is not connected\&.
.RE
.PP
\fB\-ECONNRESET\fR
.RS 4
The bus connection was closed while waiting for the response\&.
.RE
.PP
\fB\-ETIMEDOUT\fR
.RS 4
A response was not received within the given timeout\&.
.RE
.PP
\fB\-ELOOP\fR
.RS 4
The message
\fIm\fR
is addressed to its own client\&.
.RE
.PP
\fB\-ENOMEM\fR
.RS 4
Memory allocation failed\&.
.RE
.SH "NOTES"
.PP
Functions described here are available as a shared library, which can be compiled against and linked to with the
\fBlibsystemd\fR\ \&\fBpkg-config\fR(1)
file\&.
.PP
The code described here uses
\fBgetenv\fR(3), which is declared to be not multi\-thread\-safe\&. This means that the code calling the functions described here must not call
\fBsetenv\fR(3)
from a parallel thread\&. It is recommended to only do calls to
\fBsetenv()\fR
from an early phase of the program when no other threads have been started\&.
.SH "HISTORY"
.PP
\fBsd_bus_call()\fR
and
\fBsd_bus_call_async()\fR
were added in version 221\&.
.SH "SEE ALSO"
.PP
\fBsystemd\fR(1), \fBsd-bus\fR(3), \fBsd_bus_call_method\fR(3), \fBsd_bus_call_method_async\fR(3), \fBsd_bus_message_new_method_call\fR(3), \fBsd_bus_message_append\fR(3), \fBsd_bus_error\fR(3)