1SD_BUS_NEW(3) sd_bus_new SD_BUS_NEW(3)
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6 sd_bus_new, sd_bus_ref, sd_bus_unref, sd_bus_unrefp,
7 sd_bus_close_unref, sd_bus_close_unrefp, sd_bus_flush_close_unref,
8 sd_bus_flush_close_unrefp - Create a new bus object and create or
9 destroy references to it
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12 #include <systemd/sd-bus.h>
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14 int sd_bus_new(sd_bus **bus);
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16 sd_bus *sd_bus_ref(sd_bus *bus);
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18 sd_bus *sd_bus_unref(sd_bus *bus);
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20 sd_bus *sd_bus_close_unref(sd_bus *bus);
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22 sd_bus *sd_bus_flush_close_unref(sd_bus *bus);
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24 void sd_bus_unrefp(sd_bus **busp);
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26 void sd_bus_close_unrefp(sd_bus **busp);
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28 void sd_bus_flush_close_unrefp(sd_bus **busp);
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31 sd_bus_new() creates a new bus object. This object is
32 reference-counted, and will be destroyed when all references are gone.
33 Initially, the caller of this function owns the sole reference and the
34 bus object will not be connected to any bus. To connect it to a bus,
35 make sure to set an address with sd_bus_set_address(3) or a related
36 call, and then start the connection with sd_bus_start(3).
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38 In most cases, it is better to use sd_bus_default_user(3),
39 sd_bus_default_system(3) or related calls instead of the more low-level
40 sd_bus_new() and sd_bus_start(). The higher-level functions not only
41 allocate a bus object but also start the connection to a well-known bus
42 in a single function call.
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44 sd_bus_ref() increases the reference counter of bus by one.
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46 sd_bus_unref() decreases the reference counter of bus by one. Once the
47 reference count has dropped to zero, bus is destroyed and cannot be
48 used anymore, so further calls to sd_bus_ref() or sd_bus_unref() are
49 illegal.
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51 sd_bus_unrefp() is similar to sd_bus_unref() but takes a pointer to a
52 pointer to an sd_bus object. This call is useful in conjunction with
53 GCC's and LLVM's Clean-up Variable Attribute[1]. Note that this
54 function is defined as an inline function. Use a declaration like the
55 following, in order to allocate a bus object that is freed
56 automatically as the code block is left:
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58 {
59 __attribute__((cleanup(sd_bus_unrefp))) sd_bus *bus = NULL;
60 int r;
61 ...
62 r = sd_bus_default(&bus);
63 if (r < 0)
64 fprintf(stderr, "Failed to allocate bus: %s\n", strerror(-r));
65 ...
66 }
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68 sd_bus_ref() and sd_bus_unref() execute no operation if the argument is
69 NULL. sd_bus_unrefp() will first dereference its argument, which must
70 not be NULL, and will execute no operation if that is NULL.
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72 sd_bus_close_unref() is similar to sd_bus_unref(), but first executes
73 sd_bus_close(3), ensuring that the connection is terminated before the
74 reference to the connection is dropped and possibly the object freed.
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76 sd_bus_flush_close_unref() is similar to sd_bus_unref(), but first
77 executes sd_bus_flush(3) as well as sd_bus_close(3), ensuring that any
78 pending messages are synchronously flushed out before the reference to
79 the connection is dropped and possibly the object freed. This call is
80 particularly useful immediately before exiting from a program as it
81 ensures that any pending outgoing messages are written out, and
82 unprocessed but queued incoming messages released before the connection
83 is terminated and released.
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85 sd_bus_close_unrefp() is similar to sd_bus_close_unref(), but may be
86 used in GCC's and LLVM's Clean-up Variable Attribute, see above.
87 Similarly, sd_bus_flush_close_unrefp() is similar to
88 sd_bus_flush_close_unref().
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91 On success, sd_bus_new() returns 0 or a positive integer. On failure,
92 it returns a negative errno-style error code.
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94 sd_bus_ref() always returns the argument.
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96 sd_bus_unref() and sd_bus_flush_close_unref() always return NULL.
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98 Errors
99 Returned errors may indicate the following problems:
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101 -ENOMEM
102 Memory allocation failed.
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105 These APIs are implemented as a shared library, which can be compiled
106 and linked to with the libsystemd pkg-config(1) file.
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109 systemd(1), sd-bus(3), sd_bus_default_user(3),
110 sd_bus_default_system(3), sd_bus_open_user(3), sd_bus_open_system(3),
111 sd_bus_close(3)
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114 1. Clean-up Variable Attribute
115 https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html
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119systemd 251 SD_BUS_NEW(3)