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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | NOTES | SEE ALSO | NOTES | COLOPHON |
SD_BUS_NEW(3) sd_bus_new SD_BUS_NEW(3)
sd_bus_new, sd_bus_ref, sd_bus_unref, sd_bus_unrefp - Create a new
bus object and create or destroy references to it
#include <systemd/sd-bus.h>
int sd_bus_new(sd_bus **bus);
sd_bus *sd_bus_ref(sd_bus *bus);
sd_bus *sd_bus_unref(sd_bus *bus);
void sd_bus_unrefp(sd_bus **bus);
sd_bus_new() creates a new bus object. This object is
reference-counted, and will be destroyed when all references are
gone. Initially, the caller of this function owns the sole reference
and the bus object will not be connected to any bus. To connect it to
a bus, make sure to set an address with sd_bus_set_address(3) or a
related call, and then start the connection with sd_bus_start(3).
In most cases, it is a better idea to invoke sd_bus_default_user(3),
sd_bus_default_system(3) or related calls instead of the more
low-level sd_bus_new() and sd_bus_start(). The higher-level calls not
only allocate a bus object but also start the connection to a
well-known bus in a single function invocation.
sd_bus_ref() increases the reference counter of bus by one.
sd_bus_unref() decreases the reference counter of bus by one. Once
the reference count has dropped to zero, bus is destroyed and cannot
be used anymore, so further calls to sd_bus_ref() or sd_bus_unref()
are illegal.
sd_bus_unrefp() is similar to sd_bus_unref() but takes a pointer to a
pointer to an sd_bus object. This call is useful in conjunction with
GCC's and LLVM's Clean-up Variable Attribute[1]. Note that this
function is defined as inline function. Use a declaration like the
following, in order to allocate a bus object that is freed
automatically as the code block is left:
{
__attribute__((cleanup(sd_bus_unrefp)) sd_bus *bus = NULL;
int r;
...
r = sd_bus_default(&bus);
if (r < 0)
fprintf(stderr, "Failed to allocate bus: %s\n", strerror(-r));
...
}
sd_bus_ref(), sd_bus_unref() and sd_bus_unrefp() execute no operation
if the passed in bus object is NULL.
On success, sd_bus_new() returns 0 or a positive integer. On failure,
it returns a negative errno-style error code.
sd_bus_ref() always returns the argument.
sd_bus_unref() always returns NULL.
Returned errors may indicate the following problems:
-ENOMEM
Memory allocation failed.
sd_bus_new() and other functions described here are available as a
shared library, which can be compiled and linked to with the
libsystemd pkg-config(1) file.
systemd(1), sd-bus(3), sd_bus_default_user(3),
sd_bus_default_system(3), sd_bus_open_user(3), sd_bus_open_system(3)
1. Clean-up Variable Attribute
https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html
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systemd 234 SD_BUS_NEW(3)
Pages that refer to this page: sd-bus(3), sd_bus_default(3), sd_bus_message_get_cookie(3), sd_bus_message_get_monotonic_usec(3), sd_bus_request_name(3), systemd.directives(7), systemd.index(7)