sd_journal_enumerate_fields, sd_journal_restart_fields, SD_JOURNAL_FOREACH_FIELD — Read used field names from the journal
#include <systemd/sd-journal.h>
int sd_journal_enumerate_fields( | sd_journal *j, |
const char **field) ; |
void sd_journal_restart_fields( | sd_journal *j) ; |
SD_JOURNAL_FOREACH_FIELD( | sd_journal *j, |
const char *field) ; |
sd_journal_enumerate_fields()
may be used to iterate through all field names used in the
opened journal files. On each invocation the next field name is returned. The order of the returned field names is
not defined. It takes two arguments: the journal context object, plus a pointer to a constant string pointer where
the field name is stored in. The returned data is in a read-only memory map and is only valid until the next
invocation of sd_journal_enumerate_fields()
. Note that this call is subject to the data field
size threshold as controlled by sd_journal_set_data_threshold()
.
sd_journal_restart_fields()
resets the field name enumeration index to the beginning of
the list. The next invocation of sd_journal_enumerate_fields()
will return the first field
name again.
The SD_JOURNAL_FOREACH_FIELD()
macro may be used as a handy wrapper around
sd_journal_restart_fields()
and sd_journal_enumerate_fields()
.
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 retrieve the possible values a specific field can take use sd_journal_query_unique(3).
sd_journal_enumerate_fields()
returns a
positive integer if the next field name has been read, 0 when no
more field names are known, or a negative errno-style error code.
sd_journal_restart_fields()
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.
Functions described here are available as a shared
library, which can be compiled against and linked to with the
libsystemd
pkg-config(1)
file.
Use the SD_JOURNAL_FOREACH_FIELD()
macro to iterate through all field names in use in the
current journal.
/* SPDX-License-Identifier: MIT-0 */ #include <errno.h> #include <stdio.h> #include <systemd/sd-journal.h> int main(int argc, char *argv[]) { sd_journal *j; const char *field; 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; } SD_JOURNAL_FOREACH_FIELD(j, field) printf("%s\n", field); sd_journal_close(j); return 0; }
sd_journal_enumerate_fields()
,
sd_journal_restart_fields()
, and
SD_JOURNAL_FOREACH_FIELD()
were added in version 229.