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.
To enumerate all field names currently in use (and thus all suitable field parameters for
sd_journal_query_unique()
), use the
sd_journal_enumerate_fields(3)
call.
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.
All functions listed here are thread-agnostic and only a single specific thread may operate on a given object during its entire lifetime. It's safe to allocate multiple independent objects and use each from a specific thread in parallel. However, it's 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't operate on it at the very same time.
These APIs are implemented 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; }