1SD_BUS_ERROR(3) sd_bus_error SD_BUS_ERROR(3)
2
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_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
16 #include <systemd/sd-bus.h>
17 typedef struct {
19 const char *name;
20 const char *message;
21 ...
22 } sd_bus_error;
23 SD_BUS_ERROR_MAKE_CONST(name, message)
25 SD_BUS_ERROR_NULL
27 void sd_bus_error_free(sd_bus_error *e);
29 int sd_bus_error_set(sd_bus_error *e, const char *name,
31 const char *message);
32 int sd_bus_error_setf(sd_bus_error *e, const char *name,
34 const char *format, ...);
35 int sd_bus_error_set_const(sd_bus_error *e, const char *name,
37 const char *message);
38 int sd_bus_error_set_errno(sd_bus_error *e, int error);
40 int sd_bus_error_set_errnof(sd_bus_error *e, int error,
42 const char *format, ...);
43 int sd_bus_error_set_errnofv(sd_bus_error *e, int error,
45 const char *format, va_list ap);
46 int sd_bus_error_get_errno(const sd_bus_error *e);
48 int sd_bus_error_copy(sd_bus_error *dst, const sd_bus_error *e);
50 int sd_bus_error_move(sd_bus_error *dst, sd_bus_error *e);
52 int sd_bus_error_is_set(const sd_bus_error *e);
54 int sd_bus_error_has_name(const sd_bus_error *e, const char *name);
56 int sd_bus_error_has_names_sentinel(const sd_bus_error *e, ...);
58 #define sd_bus_error_has_names(e, ...)
60 sd_bus_error_has_names_sentinel(e, ..., NULL)
61
63 The sd_bus_error structure carries information about a D-Bus error
64 condition, or lack thereof. The functions described below may be used
65 to set and query fields in this structure.
66 • The name field contains a short identifier of an error. It should
68 follow the rules for error names described in the D-Bus
69 specification, subsection Valid Names[1]. A number of common,
70 standardized error names are described in sd-bus-errors(3), but
71 additional domain-specific errors may be defined by applications.
72 • The message field usually contains a human-readable string
74 describing the details, but might be NULL.
75 An unset sd_bus_error structure should have both fields initialized to
77 NULL, and signifies lack of an error, i.e. success. Assign
78 SD_BUS_ERROR_NULL to the structure in order to initialize both fields
79 to NULL. When no longer necessary, resources held by the sd_bus_error
80 structure should be destroyed with sd_bus_error_free().
81 sd_bus_error_set() sets an error structure to the specified name and
83 message strings. The strings will be copied into internal, newly
84 allocated memory. It is essential to free the contents again when they
85 are not required anymore (see above). Do not use this call on error
86 structures that have already been set. If you intend to reuse an error
87 structure, free the old data stored in it with sd_bus_error_free()
88 first.
89 sd_bus_error_set() will return an errno-like value (see errno(3))
91 determined from the specified error name name. If name is NULL, it is
92 assumed that no error occurred, and 0 is returned. If name is nonnull,
93 a negative value is always returned. If e is NULL, no error structure
94 is initialized, but name is still converted into an errno-style value.
95 Various well-known D-Bus errors are converted to well-known errno
97 counterparts, and the other ones to -EIO. See sd-bus-errors(3) for a
98 list of well-known error names. Additional error mappings may be
99 defined with sd_bus_error_add_map(3).
100 sd_bus_error_set() is designed to be conveniently used in a return
102 statement. If message is NULL, no message is set. This call can fail if
103 no memory may be allocated for the name and message strings, in which
104 case an SD_BUS_ERROR_NO_MEMORY error will be set instead and -ENOMEM
105 returned.
106 sd_bus_error_setf() is similar to sd_bus_error_set(), but takes a
108 printf(3) format string and corresponding arguments to generate the
109 message field.
110 sd_bus_error_set_const() is similar to sd_bus_error_set(), but the
112 string parameters are not copied internally, and must hence remain
113 constant and valid for the lifetime of e. Use this call to avoid memory
114 allocations when setting error structures. Since this call does not
115 allocate memory, it will not fail with an out-of-memory condition as
116 sd_bus_error_set() may, as described above. Alternatively, the
117 SD_BUS_ERROR_MAKE_CONST() macro may be used to generate a literal,
118 constant bus error structure on-the-fly.
119 sd_bus_error_set_errno() will immediately return 0 if the specified
121 error parameter error is 0. Otherwise, it will set name from an
122 errno-like value that is converted to a D-Bus error. strerror_r(3)
123 will be used to set message. Well-known D-Bus error names will be used
124 for name if applicable, otherwise a name in the "System.Error."
125 namespace will be generated. The sign of the specified error number is
126 ignored and the absolute value is used implicitly. If the specified
127 error error is non-zero, the call always returns a negative value, for
128 convenient usage in return statements. This call might fail due to lack
129 of memory, in which case an SD_BUS_ERROR_NO_MEMORY error is set
130 instead, and -ENOMEM is returned.
131 sd_bus_error_set_errnof() is similar to sd_bus_error_set_errno(), but
133 in addition to error, takes a printf(3) format string and corresponding
134 arguments. The message field will be generated from format and the
135 arguments.
136 sd_bus_error_set_errnofv() is similar to sd_bus_error_set_errnof(), but
138 takes the format string parameters as va_arg(3) parameter list.
139 sd_bus_error_get_errno() converts the name field of an error structure
141 to an errno-like (positive) value using the same rules as
142 sd_bus_error_set(). If e is NULL, 0 will be returned.
143 sd_bus_error_copy() will initialize dst using the values in e, if e has
145 been set with an error value before. Otherwise, it will return
146 immediately. If the strings in e were set using
147 sd_bus_error_set_const(), they will be shared. Otherwise, they will be
148 copied. Before this call, dst must be unset, i.e. either freshly
149 initialized with NULL or reset using sd_bus_error_free().
150 sd_bus_error_copy() generally returns 0 or a negative errno-like value
152 based on the input parameter e: 0 if it was unset and a negative
153 integer if it was set to some error, similarly to sd_bus_error_set().
154 It may however also return an error generated internally, for example
155 -ENOMEM if a memory allocation fails.
156 sd_bus_error_move() is similar to sd_bus_error_copy(), but will move
158 any error information from e into dst, resetting the former. This
159 function cannot fail, as no new memory is allocated. Note that if e is
160 not set, dst is initialized to SD_BUS_ERROR_NULL. Moreover, if dst is
161 NULL no operation is executed on it and resources held by e are freed
162 and reset. Returns a converted errno-like, non-positive error value.
163 sd_bus_error_is_set() will return a non-zero value if e is non-NULL and
165 an error has been set, false otherwise.
166 sd_bus_error_has_name() will return a non-zero value if e is non-NULL
168 and an error with the same name has been set, false otherwise.
169 sd_bus_error_has_names_sentinel() is similar to
171 sd_bus_error_has_name(), but takes multiple names to check against. The
172 list must be terminated with NULL. sd_bus_error_has_names() is a macro
173 wrapper around sd_bus_error_has_names_sentinel() that adds the NULL
174 sentinel automatically.
175 sd_bus_error_free() will destroy resources held by e. The parameter
177 itself will not be deallocated, and must be free(3)d by the caller if
178 necessary. The function may also be called safely on unset errors
179 (error structures with both fields set to NULL), in which case it
180 performs no operation. This call will reset the error structure after
181 freeing the data, so that all fields are set to NULL. The structure may
182 be reused afterwards.
183
185 sd_bus_error is not reference-counted. Users should destroy resources
186 held by it by calling sd_bus_error_free(). Usually, error structures
187 are allocated on the stack or passed in as function parameters, but
188 they may also be allocated dynamically, in which case it is the duty of
189 the caller to free(3) the memory held by the structure itself after
190 freeing its contents with sd_bus_error_free().
191
193 The functions sd_bus_error_set(), sd_bus_error_setf(), and
194 sd_bus_error_set_const() always return 0 when the specified error value
195 is NULL, and a negative errno-like value corresponding to the name
196 parameter otherwise. The functions sd_bus_error_set_errno(),
197 sd_bus_error_set_errnof() and sd_bus_error_set_errnofv(), return 0 when
198 the specified error value is 0, and a negative errno-like value
199 corresponding to the error parameter otherwise. If an error occurs
200 internally, one of the negative error values listed below will be
201 returned. This allows those functions to be conveniently used in a
202 return statement, see the example below.
203 sd_bus_error_get_errno() returns false when e is NULL, and a positive
205 errno value mapped from e->name otherwise.
206 sd_bus_error_copy() and sd_bus_error_move() return a negative error
208 value converted from the source error, and zero if the error has not
209 been set. This allows those functions to be conveniently used in a
210 return statement, see the example below.
211 sd_bus_error_is_set() returns a non-zero value when e and the name
213 field are non-NULL, zero otherwise.
214 sd_bus_error_has_name(), sd_bus_error_has_names(), and
216 sd_bus_error_has_names_sentinel() return a non-zero value when e is
217 non-NULL and the name field is equal to one of the given names, zero
218 otherwise.
219 Errors
221 Return value may indicate the following problems in the invocation of
222 the function itself:
223 -EINVAL
225 Error was already set in the sd_bus_error structure when one the
226 error-setting functions was called.
227 -ENOMEM
229 Memory allocation failed.
230 On success, sd_bus_error_set(), sd_bus_error_setf(),
232 sd_bus_error_set_const(), sd_bus_error_set_errno(),
233 sd_bus_error_set_errnof(), sd_bus_error_set_errnofv(),
234 sd_bus_error_copy(), and sd_bus_error_move() will return a negative
235 converted errno-style value, or 0 if the error parameter is NULL or
236 unset. D-Bus errors are converted to the integral errno-style value,
237 and the mapping mechanism is extensible, see the discussion above. This
238 effectively means that almost any negative errno-style value can be
239 returned.
240
242 Example 1. Using the negative return value to propagate an error
243 /* SPDX-License-Identifier: CC0-1.0 */
245 #include <errno.h>
247 #include <string.h>
248 #include <unistd.h>
249 #include <sd-bus.h>
250 int writer_with_negative_errno_return(int fd, sd_bus_error *error) {
252 const char *message = "Hello, World!\n";
253 ssize_t n = write(fd, message, strlen(message));
255 if (n >= 0)
256 return n; /* On success, return the number of bytes written, possibly 0. */
257 /* On error, initialize the error structure, and also propagate the errno
259 * value that write(2) set for us. */
260 return sd_bus_error_set_errnof(error, errno, "Failed to write to fd %i: %m", fd);
261 }
262
264 These APIs are implemented as a shared library, which can be compiled
265 and linked to with the libsystemd pkg-config(1) file.
266
268 systemd(1), sd-bus(3), sd-bus-errors(3), sd_bus_error_add_map(3),
269 errno(3), strerror_r(3)
270
272 1. Valid Names
273 http://dbus.freedesktop.org/doc/dbus-specification.html#message-protocol-names
274systemd 251 SD_BUS_ERROR(3)