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
|
'\" t
.TH "SD_JOURNAL_QUERY_UNIQUE" "3" "" "systemd 241" "sd_journal_query_unique"
.\" -----------------------------------------------------------------
.\" * Define some portability stuff
.\" -----------------------------------------------------------------
.\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
.\" http://bugs.debian.org/507673
.\" http://lists.gnu.org/archive/html/groff/2009-02/msg00013.html
.\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
.ie \n(.g .ds Aq \(aq
.el .ds Aq '
.\" -----------------------------------------------------------------
.\" * set default formatting
.\" -----------------------------------------------------------------
.\" disable hyphenation
.nh
.\" disable justification (adjust text to left margin only)
.ad l
.\" -----------------------------------------------------------------
.\" * MAIN CONTENT STARTS HERE *
.\" -----------------------------------------------------------------
.SH "NAME"
sd_journal_query_unique, sd_journal_enumerate_unique, sd_journal_restart_unique, SD_JOURNAL_FOREACH_UNIQUE \- Read unique data fields from the journal
.SH "SYNOPSIS"
.sp
.ft B
.nf
#include <systemd/sd\-journal\&.h>
.fi
.ft
.HP \w'int\ sd_journal_query_unique('u
.BI "int sd_journal_query_unique(sd_journal\ *" "j" ", const\ char\ *" "field" ");"
.HP \w'int\ sd_journal_enumerate_unique('u
.BI "int sd_journal_enumerate_unique(sd_journal\ *" "j" ", const\ void\ **" "data" ", size_t\ *" "length" ");"
.HP \w'void\ sd_journal_restart_unique('u
.BI "void sd_journal_restart_unique(sd_journal\ *" "j" ");"
.HP \w'SD_JOURNAL_FOREACH_UNIQUE('u
.BI "SD_JOURNAL_FOREACH_UNIQUE(sd_journal\ *" "j" ", const\ void\ *" "data" ", size_t\ " "length" ");"
.SH "DESCRIPTION"
.PP
\fBsd_journal_query_unique()\fR
queries the journal for all unique values the specified field can take\&. It takes two arguments: the journal to query and the field name to look for\&. Well\-known field names are listed on
\fBsystemd.journal-fields\fR(7)\&. Field names must be specified without a trailing \*(Aq=\*(Aq\&. After this function has been executed successfully the field values may be queried using
\fBsd_journal_enumerate_unique()\fR\&. Invoking this call a second time will change the field name being queried and reset the enumeration index to the first field value that matches\&.
.PP
\fBsd_journal_enumerate_unique()\fR
may be used to iterate through all data fields which match the previously selected field name as set with
\fBsd_journal_query_unique()\fR\&. On each invocation the next field data matching the field name is returned\&. The order of the returned data fields is not defined\&. It takes three arguments: the journal context object, plus a pair of pointers to pointer/size variables where the data object and its size shall be stored in\&. The returned data is in a read\-only memory map and is only valid until the next invocation of
\fBsd_journal_enumerate_unique()\fR\&. Note that the data returned will be prefixed with the field name and \*(Aq=\*(Aq\&. Note that this call is subject to the data field size threshold as controlled by
\fBsd_journal_set_data_threshold()\fR\&.
.PP
\fBsd_journal_restart_unique()\fR
resets the data enumeration index to the beginning of the list\&. The next invocation of
\fBsd_journal_enumerate_unique()\fR
will return the first field data matching the field name again\&.
.PP
Note that the
\fBSD_JOURNAL_FOREACH_UNIQUE()\fR
macro may be used as a handy wrapper around
\fBsd_journal_restart_unique()\fR
and
\fBsd_journal_enumerate_unique()\fR\&.
.PP
Note that these functions currently are not influenced by matches set with
\fBsd_journal_add_match()\fR
but this might change in a later version of this software\&.
.PP
To enumerate all field names currently in use (and thus all suitable field parameters for
\fBsd_journal_query_unique()\fR), use the
\fBsd_journal_enumerate_fields\fR(3)
call\&.
.SH "RETURN VALUE"
.PP
\fBsd_journal_query_unique()\fR
returns 0 on success or a negative errno\-style error code\&.
\fBsd_journal_enumerate_unique()\fR
returns a positive integer if the next field data has been read, 0 when no more fields are known, or a negative errno\-style error code\&.
\fBsd_journal_restart_unique()\fR
returns nothing\&.
.SH "NOTES"
.PP
All functions listed here are thread\-agnostic and only a single specific thread may operate on a given object during its entire lifetime\&. It\*(Aqs safe to allocate multiple independent objects and use each from a specific thread in parallel\&. However, it\*(Aqs not safe to allocate such an object in one thread, and operate or free it from any other, even if locking is used to ensure these threads don\*(Aqt operate on it at the very same time\&.
.PP
These APIs are implemented as a shared library, which can be compiled and linked to with the
\fBlibsystemd\fR\ \&\fBpkg-config\fR(1)
file\&.
.SH "EXAMPLES"
.PP
Use the
\fBSD_JOURNAL_FOREACH_UNIQUE\fR
macro to iterate through all values a field of the journal can take\&. The following example lists all unit names referenced in the journal:
.sp
.if n \{\
.RS 4
.\}
.nf
#include <stdio\&.h>
#include <string\&.h>
#include <systemd/sd\-journal\&.h>
int main(int argc, char *argv[]) {
sd_journal *j;
const void *d;
size_t l;
int r;
r = sd_journal_open(&j, SD_JOURNAL_LOCAL_ONLY);
if (r < 0) {
fprintf(stderr, "Failed to open journal: %s\en", strerror(\-r));
return 1;
}
r = sd_journal_query_unique(j, "_SYSTEMD_UNIT");
if (r < 0) {
fprintf(stderr, "Failed to query journal: %s\en", strerror(\-r));
return 1;
}
SD_JOURNAL_FOREACH_UNIQUE(j, d, l)
printf("%\&.*s\en", (int) l, (const char*) d);
sd_journal_close(j);
return 0;
}
.fi
.if n \{\
.RE
.\}
.SH "SEE ALSO"
.PP
\fBsystemd\fR(1),
\fBsystemd.journal-fields\fR(7),
\fBsd-journal\fR(3),
\fBsd_journal_open\fR(3),
\fBsd_journal_enumerate_fields\fR(3),
\fBsd_journal_get_data\fR(3),
\fBsd_journal_add_match\fR(3)
|
