From 03ecdfcc404d4066dfae119d3ce27266fc0bfa88 Mon Sep 17 00:00:00 2001 From: Lennart Poettering Date: Wed, 27 Jan 2016 18:59:29 +0100 Subject: [PATCH 1/1] sd-journal: add an API to enumerate known field names of the journal This adds two new calls to get the list of all journal fields names currently in use. This is the low-level support to implement the feature requested in #2176 in a more optimized way. --- man/sd_journal_enumerate_fields.xml | 161 ++++++++++++++++++++++++++++ 1 file changed, 161 insertions(+) create mode 100644 man/sd_journal_enumerate_fields.xml diff --git a/man/sd_journal_enumerate_fields.xml b/man/sd_journal_enumerate_fields.xml new file mode 100644 index 000000000..7d43f6f5a --- /dev/null +++ b/man/sd_journal_enumerate_fields.xml @@ -0,0 +1,161 @@ + + + + + + + + + sd_journal_enumerate_fields + elogind + + + + Developer + Lennart + Poettering + lennart@poettering.net + + + + + + sd_journal_enumerate_fields + 3 + + + + sd_journal_enumerate_fields + sd_journal_restart_fields + SD_JOURNAL_FOREACH_FIELD + Read used field names from the journal + + + + + #include <elogind/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 + + + + + + + Description + + 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_unique3. + + + + Return Value + + 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. + + + + Notes + + The sd_journal_enumerate_fields() and sd_journal_restart_fields() + interfaces are available as a shared library, which can be compiled and linked to with the + libelogind pkg-config1 file. + + + + Examples + + Use the SD_JOURNAL_FOREACH_FIELD macro to iterate through all field names in use in the + current journal. + + #include <stdio.h> +#include <string.h> +#include <elogind/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; +} + + + + + See Also + + + elogind1, + elogind.journal-fields7, + sd-journal3, + sd_journal_open3, + sd_journal_query_unique3, + sd_journal_get_data3, + sd_journal_add_match3 + + + + -- 2.30.2