1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
|
/* SPDX-License-Identifier: MIT-0 */
/* Implements the LogControl1 interface as per specification:
* https://www.freedesktop.org/software/systemd/man/org.freedesktop.LogControl1.html
*
* Compile with 'cc logcontrol-example.c $(pkg-config --libs --cflags libsystemd)'
*
* To get and set properties via busctl:
*
* $ busctl --user get-property org.freedesktop.Example \
* /org/freedesktop/LogControl1 \
* org.freedesktop.LogControl1 \
* SyslogIdentifier
* s "example"
* $ busctl --user get-property org.freedesktop.Example \
* /org/freedesktop/LogControl1 \
* org.freedesktop.LogControl1 \
* LogTarget
* s "journal"
* $ busctl --user get-property org.freedesktop.Example \
* /org/freedesktop/LogControl1 \
* org.freedesktop.LogControl1 \
* LogLevel
* s "info"
* $ busctl --user set-property org.freedesktop.Example \
* /org/freedesktop/LogControl1 \
* org.freedesktop.LogControl1 \
* LogLevel \
* "s" debug
* $ busctl --user get-property org.freedesktop.Example \
* /org/freedesktop/LogControl1 \
* org.freedesktop.LogControl1 \
* LogLevel
* s "debug"
*/
#include <errno.h>
#include <stdlib.h>
#include <stdio.h>
#include <syslog.h>
#include <systemd/sd-bus.h>
#include <systemd/sd-journal.h>
#define _cleanup_(f) __attribute__((cleanup(f)))
#define check(log_level, x) ({ \
int _r = (x); \
errno = _r < 0 ? -_r : 0; \
sd_journal_print((log_level), #x ": %m"); \
if (_r < 0) \
return EXIT_FAILURE; \
})
typedef enum LogTarget {
LOG_TARGET_JOURNAL,
LOG_TARGET_KMSG,
LOG_TARGET_SYSLOG,
LOG_TARGET_CONSOLE,
_LOG_TARGET_MAX,
} LogTarget;
static const char* const log_target_table[_LOG_TARGET_MAX] = {
[LOG_TARGET_JOURNAL] = "journal",
[LOG_TARGET_KMSG] = "kmsg",
[LOG_TARGET_SYSLOG] = "syslog",
[LOG_TARGET_CONSOLE] = "console",
};
static const char* const log_level_table[LOG_DEBUG + 1] = {
[LOG_EMERG] = "emerg",
[LOG_ALERT] = "alert",
[LOG_CRIT] = "crit",
[LOG_ERR] = "err",
[LOG_WARNING] = "warning",
[LOG_NOTICE] = "notice",
[LOG_INFO] = "info",
[LOG_DEBUG] = "debug",
};
typedef struct object {
const char *syslog_identifier;
LogTarget log_target;
int log_level;
} object;
static int property_get(
sd_bus *bus,
const char *path,
const char *interface,
const char *property,
sd_bus_message *reply,
void *userdata,
sd_bus_error *error) {
object *o = userdata;
if (strcmp(property, "LogLevel") == 0)
return sd_bus_message_append(reply, "s", log_level_table[o->log_level]);
if (strcmp(property, "LogTarget") == 0)
return sd_bus_message_append(reply, "s", log_target_table[o->log_target]);
if (strcmp(property, "SyslogIdentifier") == 0)
return sd_bus_message_append(reply, "s", o->syslog_identifier);
return sd_bus_error_setf(error,
SD_BUS_ERROR_UNKNOWN_PROPERTY,
"Unknown property '%s'",
property);
}
static int property_set(
sd_bus *bus,
const char *path,
const char *interface,
const char *property,
sd_bus_message *message,
void *userdata,
sd_bus_error *error) {
object *o = userdata;
const char *value;
int r;
r = sd_bus_message_read(message, "s", &value);
if (r < 0)
return r;
if (strcmp(property, "LogLevel") == 0) {
for (int i = 0; i < LOG_DEBUG + 1; i++)
if (strcmp(value, log_level_table[i]) == 0) {
o->log_level = i;
setlogmask(LOG_UPTO(i));
return 0;
}
return sd_bus_error_setf(error,
SD_BUS_ERROR_INVALID_ARGS,
"Invalid value for LogLevel: '%s'",
value);
}
if (strcmp(property, "LogTarget") == 0) {
for (LogTarget i = 0; i < _LOG_TARGET_MAX; i++)
if (strcmp(value, log_target_table[i]) == 0) {
o->log_target = i;
return 0;
}
return sd_bus_error_setf(error,
SD_BUS_ERROR_INVALID_ARGS,
"Invalid value for LogTarget: '%s'",
value);
}
return sd_bus_error_setf(error,
SD_BUS_ERROR_UNKNOWN_PROPERTY,
"Unknown property '%s'",
property);
}
/* https://www.freedesktop.org/software/systemd/man/sd_bus_add_object.html
*/
static const sd_bus_vtable vtable[] = {
SD_BUS_VTABLE_START(0),
SD_BUS_WRITABLE_PROPERTY(
"LogLevel", "s",
property_get, property_set,
0,
0),
SD_BUS_WRITABLE_PROPERTY(
"LogTarget", "s",
property_get, property_set,
0,
0),
SD_BUS_PROPERTY(
"SyslogIdentifier", "s",
property_get,
0,
SD_BUS_VTABLE_PROPERTY_CONST),
SD_BUS_VTABLE_END
};
int main(int argc, char **argv) {
/* The bus should be relinquished before the program terminates. The cleanup
* attribute allows us to do it nicely and cleanly whenever we exit the
* block.
*/
_cleanup_(sd_bus_flush_close_unrefp) sd_bus *bus = NULL;
object o = {
.log_level = LOG_INFO,
.log_target = LOG_TARGET_JOURNAL,
.syslog_identifier = "example",
};
/* https://man7.org/linux/man-pages/man3/setlogmask.3.html
* Programs using syslog() instead of sd_journal can use this API to cut logs
* emission at the source.
*/
setlogmask(LOG_UPTO(o.log_level));
/* Acquire a connection to the bus, letting the library work out the details.
* https://www.freedesktop.org/software/systemd/man/sd_bus_default.html
*/
check(o.log_level, sd_bus_default(&bus));
/* Publish an interface on the bus, specifying our well-known object access
* path and public interface name.
* https://www.freedesktop.org/software/systemd/man/sd_bus_add_object.html
* https://dbus.freedesktop.org/doc/dbus-tutorial.html
*/
check(o.log_level, sd_bus_add_object_vtable(bus, NULL,
"/org/freedesktop/LogControl1",
"org.freedesktop.LogControl1",
vtable,
&o));
/* By default the service is assigned an ephemeral name. Also add a fixed
* one, so that clients know whom to call.
* https://www.freedesktop.org/software/systemd/man/sd_bus_request_name.html
*/
check(o.log_level, sd_bus_request_name(bus, "org.freedesktop.Example", 0));
for (;;) {
/* https://www.freedesktop.org/software/systemd/man/sd_bus_wait.html
*/
check(o.log_level, sd_bus_wait(bus, UINT64_MAX));
/* https://www.freedesktop.org/software/systemd/man/sd_bus_process.html
*/
check(o.log_level, sd_bus_process(bus, NULL));
}
/* https://www.freedesktop.org/software/systemd/man/sd_bus_release_name.html
*/
check(o.log_level, sd_bus_release_name(bus, "org.freedesktop.Example"));
return 0;
}
|
