1SD_BUS_ERROR(3)                  sd_bus_error                  SD_BUS_ERROR(3)
2
3
4

NAME

6       sd_bus_error, SD_BUS_ERROR_MAKE_CONST, SD_BUS_ERROR_NULL,
7       sd_bus_error_free, sd_bus_error_set, sd_bus_error_setf,
8       sd_bus_error_setfv, sd_bus_error_set_const, sd_bus_error_set_errno,
9       sd_bus_error_set_errnof, sd_bus_error_set_errnofv,
10       sd_bus_error_get_errno, sd_bus_error_copy, sd_bus_error_move,
11       sd_bus_error_is_set, sd_bus_error_has_name,
12       sd_bus_error_has_names_sentinel, sd_bus_error_has_names - sd-bus error
13       handling
14

SYNOPSIS

16       #include <systemd/sd-bus.h>
17
18       typedef struct {
19               const char *name;
20               const char *message;
21               ...
22       } sd_bus_error;
23
24       SD_BUS_ERROR_MAKE_CONST(name, message)
25
26       SD_BUS_ERROR_NULL
27
28       void sd_bus_error_free(sd_bus_error *e);
29
30       int sd_bus_error_set(sd_bus_error *e, const char *name,
31                            const char *message);
32
33       int sd_bus_error_setf(sd_bus_error *e, const char *name,
34                             const char *format, ...);
35
36       int sd_bus_error_setfv(sd_bus_error *e, const char *name,
37                              const char *format, va_list ap);
38
39       int sd_bus_error_set_const(sd_bus_error *e, const char *name,
40                                  const char *message);
41
42       int sd_bus_error_set_errno(sd_bus_error *e, int error);
43
44       int sd_bus_error_set_errnof(sd_bus_error *e, int error,
45                                   const char *format, ...);
46
47       int sd_bus_error_set_errnofv(sd_bus_error *e, int error,
48                                    const char *format, va_list ap);
49
50       int sd_bus_error_get_errno(const sd_bus_error *e);
51
52       int sd_bus_error_copy(sd_bus_error *dst, const sd_bus_error *e);
53
54       int sd_bus_error_move(sd_bus_error *dst, sd_bus_error *e);
55
56       int sd_bus_error_is_set(const sd_bus_error *e);
57
58       int sd_bus_error_has_name(const sd_bus_error *e, const char *name);
59
60       int sd_bus_error_has_names_sentinel(const sd_bus_error *e, ...);
61
62       #define sd_bus_error_has_names(e, ...)
63       sd_bus_error_has_names_sentinel(e, ..., NULL)
64

DESCRIPTION

66       The sd_bus_error structure carries information about a D-Bus error
67       condition, or lack thereof. The functions described below may be used
68       to set and query fields in this structure.
69
70       •   The name field contains a short identifier of an error. It should
71           follow the rules for error names described in the D-Bus
72           specification, subsection Valid Names[1]. A number of common,
73           standardized error names are described in sd-bus-errors(3), but
74           additional domain-specific errors may be defined by applications.
75
76       •   The message field usually contains a human-readable string
77           describing the details, but might be NULL.
78
79       An unset sd_bus_error structure should have both fields initialized to
80       NULL, and signifies lack of an error, i.e. success. Assign
81       SD_BUS_ERROR_NULL to the structure in order to initialize both fields
82       to NULL. When no longer necessary, resources held by the sd_bus_error
83       structure should be destroyed with sd_bus_error_free().
84
85       sd_bus_error_set() sets an error structure to the specified name and
86       message strings. The strings will be copied into internal, newly
87       allocated memory. It is essential to free the contents again when they
88       are not required anymore (see above). Do not use this call on error
89       structures that have already been set. If you intend to reuse an error
90       structure, free the old data stored in it with sd_bus_error_free()
91       first.
92
93       sd_bus_error_set() will return an errno-like value (see errno(3))
94       determined from the specified error name name. If name is NULL, it is
95       assumed that no error occurred, and 0 is returned. If name is nonnull,
96       a negative value is always returned. If e is NULL, no error structure
97       is initialized, but name is still converted into an errno-style value.
98
99       Various well-known D-Bus errors are converted to well-known errno
100       counterparts, and the other ones to -EIO. See sd-bus-errors(3) for a
101       list of well-known error names. Additional error mappings may be
102       defined with sd_bus_error_add_map(3).
103
104       sd_bus_error_set() is designed to be conveniently used in a return
105       statement. If message is NULL, no message is set. This call can fail if
106       no memory may be allocated for the name and message strings, in which
107       case an SD_BUS_ERROR_NO_MEMORY error will be set instead and -ENOMEM
108       returned.
109
110       sd_bus_error_setf() and sd_bus_error_setfv() are similar to
111       sd_bus_error_set(), but take a printf(3) format string and
112       corresponding arguments to generate the message field.
113       sd_bus_error_setf() uses variadic arguments, and sd_bus_error_setfv()
114       accepts the arguments as a va_arg(3) parameter list.
115
116       sd_bus_error_set_const() is similar to sd_bus_error_set(), but the
117       string parameters are not copied internally, and must hence remain
118       constant and valid for the lifetime of e. Use this call to avoid memory
119       allocations when setting error structures. Since this call does not
120       allocate memory, it will not fail with an out-of-memory condition as
121       sd_bus_error_set() may, as described above. Alternatively, the
122       SD_BUS_ERROR_MAKE_CONST() macro may be used to generate a literal,
123       constant bus error structure on-the-fly.
124
125       sd_bus_error_set_errno() will immediately return 0 if the specified
126       error parameter error is 0. Otherwise, it will set name from an
127       errno-like value that is converted to a D-Bus error.  strerror_r(3)
128       will be used to set message. Well-known D-Bus error names will be used
129       for name if applicable, otherwise a name in the "System.Error."
130       namespace will be generated. The sign of the specified error number is
131       ignored and the absolute value is used implicitly. If the specified
132       error error is non-zero, the call always returns a negative value, for
133       convenient usage in return statements. This call might fail due to lack
134       of memory, in which case an SD_BUS_ERROR_NO_MEMORY error is set
135       instead, and -ENOMEM is returned.
136
137       sd_bus_error_set_errnof() and sd_bus_error_set_errnof() are similar to
138       sd_bus_error_set_errno(), but in addition to error, take a printf(3)
139       format string and corresponding arguments. The message field will be
140       generated from format and the arguments.  sd_bus_error_set_errnof()
141       uses variadic arguments, and sd_bus_error_set_errnofv() accepts the
142       arguments as a va_arg(3) parameter list.
143
144       sd_bus_error_get_errno() converts the name field of an error structure
145       to an errno-like (positive) value using the same rules as
146       sd_bus_error_set(). If e is NULL, 0 will be returned.
147
148       sd_bus_error_copy() will initialize dst using the values in e, if e has
149       been set with an error value before. Otherwise, it will return
150       immediately. If the strings in e were set using
151       sd_bus_error_set_const(), they will be shared. Otherwise, they will be
152       copied. Before this call, dst must be unset, i.e. either freshly
153       initialized with NULL or reset using sd_bus_error_free().
154
155       sd_bus_error_copy() generally returns 0 or a negative errno-like value
156       based on the input parameter e: 0 if it was unset and a negative
157       integer if it was set to some error, similarly to sd_bus_error_set().
158       It may however also return an error generated internally, for example
159       -ENOMEM if a memory allocation fails.
160
161       sd_bus_error_move() is similar to sd_bus_error_copy(), but will move
162       any error information from e into dst, resetting the former. This
163       function cannot fail, as no new memory is allocated. Note that if e is
164       not set, dst is initialized to SD_BUS_ERROR_NULL. Moreover, if dst is
165       NULL no operation is executed on it and resources held by e are freed
166       and reset. Returns a converted errno-like, non-positive error value.
167
168       sd_bus_error_is_set() will return a non-zero value if e is non-NULL and
169       an error has been set, false otherwise.
170
171       sd_bus_error_has_name() will return a non-zero value if e is non-NULL
172       and an error with the same name has been set, false otherwise.
173
174       sd_bus_error_has_names_sentinel() is similar to
175       sd_bus_error_has_name(), but takes multiple names to check against. The
176       list must be terminated with NULL.  sd_bus_error_has_names() is a macro
177       wrapper around sd_bus_error_has_names_sentinel() that adds the NULL
178       sentinel automatically.
179
180       sd_bus_error_free() will destroy resources held by e. The parameter
181       itself will not be deallocated, and must be free(3)d by the caller if
182       necessary. The function may also be called safely on unset errors
183       (error structures with both fields set to NULL), in which case it
184       performs no operation. This call will reset the error structure after
185       freeing the data, so that all fields are set to NULL. The structure may
186       be reused afterwards.
187

REFERENCE OWNERSHIP

189       sd_bus_error is not reference-counted. Users should destroy resources
190       held by it by calling sd_bus_error_free(). Usually, error structures
191       are allocated on the stack or passed in as function parameters, but
192       they may also be allocated dynamically, in which case it is the duty of
193       the caller to free(3) the memory held by the structure itself after
194       freeing its contents with sd_bus_error_free().
195

RETURN VALUE

197       The functions sd_bus_error_set(), sd_bus_error_setf(), and
198       sd_bus_error_set_const() always return 0 when the specified error value
199       is NULL, and a negative errno-like value corresponding to the name
200       parameter otherwise. The functions sd_bus_error_set_errno(),
201       sd_bus_error_set_errnof() and sd_bus_error_set_errnofv(), return 0 when
202       the specified error value is 0, and a negative errno-like value
203       corresponding to the error parameter otherwise. If an error occurs
204       internally, one of the negative error values listed below will be
205       returned. This allows those functions to be conveniently used in a
206       return statement, see the example below.
207
208       sd_bus_error_get_errno() returns false when e is NULL, and a positive
209       errno value mapped from e->name otherwise.
210
211       sd_bus_error_copy() and sd_bus_error_move() return a negative error
212       value converted from the source error, and zero if the error has not
213       been set. This allows those functions to be conveniently used in a
214       return statement, see the example below.
215
216       sd_bus_error_is_set() returns a non-zero value when e and the name
217       field are non-NULL, zero otherwise.
218
219       sd_bus_error_has_name(), sd_bus_error_has_names(), and
220       sd_bus_error_has_names_sentinel() return a non-zero value when e is
221       non-NULL and the name field is equal to one of the given names, zero
222       otherwise.
223
224   Errors
225       Return value may indicate the following problems in the invocation of
226       the function itself:
227
228       -EINVAL
229           Error was already set in the sd_bus_error structure when one the
230           error-setting functions was called.
231
232       -ENOMEM
233           Memory allocation failed.
234
235       On success, sd_bus_error_set(), sd_bus_error_setf(),
236       sd_bus_error_set_const(), sd_bus_error_set_errno(),
237       sd_bus_error_set_errnof(), sd_bus_error_set_errnofv(),
238       sd_bus_error_copy(), and sd_bus_error_move() will return a negative
239       converted errno-style value, or 0 if the error parameter is NULL or
240       unset. D-Bus errors are converted to the integral errno-style value,
241       and the mapping mechanism is extensible, see the discussion above. This
242       effectively means that almost any negative errno-style value can be
243       returned.
244

EXAMPLES

246       Example 1. Using the negative return value to propagate an error
247
248           /* SPDX-License-Identifier: MIT-0 */
249
250           #include <errno.h>
251           #include <string.h>
252           #include <unistd.h>
253           #include <sd-bus.h>
254
255           int writer_with_negative_errno_return(int fd, sd_bus_error *error) {
256             const char *message = "Hello, World!\n";
257
258             ssize_t n = write(fd, message, strlen(message));
259             if (n >= 0)
260               return n; /* On success, return the number of bytes written, possibly 0. */
261
262             /* On error, initialize the error structure, and also propagate the errno
263              * value that write(2) set for us. */
264             return sd_bus_error_set_errnof(error, errno, "Failed to write to fd %i: %m", fd);
265           }
266

NOTES

268       These APIs are implemented as a shared library, which can be compiled
269       and linked to with the libsystemd pkg-config(1) file.
270

SEE ALSO

272       systemd(1), sd-bus(3), sd-bus-errors(3), sd_bus_error_add_map(3),
273       errno(3), strerror_r(3)
274

NOTES

276        1. Valid Names
277           https://dbus.freedesktop.org/doc/dbus-specification.html#message-protocol-names
278
279
280
281systemd 253                                                    SD_BUS_ERROR(3)
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