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; }