sd_journal_query_unique, sd_journal_enumerate_unique, sd_journal_restart_unique, SD_JOURNAL_FOREACH_UNIQUE — Read unique data fields from the journal
#include <systemd/sd-journal.h>
int sd_journal_query_unique( | sd_journal *j, |
const char *field); |
int sd_journal_enumerate_unique( | sd_journal *j, |
| const void **data, | |
size_t *length); |
void sd_journal_restart_unique( | sd_journal *j); |
SD_JOURNAL_FOREACH_UNIQUE( | sd_journal *j, |
| const void *data, | |
size_t length); |
sd_journal_query_unique()
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
systemd.journal-fields(7). Field
names must be specified without a trailing '='. After
this function has been executed successfully the field
values may be queried using
sd_journal_enumerate_unique(). 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.
sd_journal_enumerate_unique()
may be used to iterate through all data fields which
match the previously selected field name as set with
sd_journal_query_unique(). 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
sd_journal_enumerate_unique(). Note
that the data returned will be prefixed with the field
name and '='. Note that this call is subject to the
data field size threshold as controlled by
sd_journal_set_data_threshold().
sd_journal_restart_unique()
resets the data enumeration index to the beginning of
the list. The next invocation of
sd_journal_enumerate_unique()
will return the first field data matching the field
name again.
Note that the
SD_JOURNAL_FOREACH_UNIQUE() macro
may be used as a handy wrapper around
sd_journal_restart_unique() and
sd_journal_enumerate_unique().
Note that these functions currently are not
influenced by matches set with
sd_journal_add_match() but this
might change in a later version of this
software.
sd_journal_query_unique()
returns 0 on success or a negative errno-style error
code. sd_journal_enumerate_unique()
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. sd_journal_restart_unique()
returns nothing.
The sd_journal_query_unique(),
sd_journal_enumerate_unique() and
sd_journal_restart_unique()
interfaces are available as a shared library, which can
be compiled and linked to with the
libsystemd pkg-config(1)
file.
Use the
SD_JOURNAL_FOREACH_UNIQUE macro
to iterate through all values a field of the journal
can take. The following example lists all unit names
referenced in the journal:
#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\n", strerror(-r));
return 1;
}
r = sd_journal_query_unique(j, "_SYSTEMD_UNIT");
if (r < 0) {
fprintf(stderr, "Failed to query journal: %s\n", strerror(-r));
return 1;
}
SD_JOURNAL_FOREACH_UNIQUE(j, d, l)
printf("%.*s\n", (int) l, (const char*) d);
sd_journal_close(j);
return 0;
}