sd_journal_get_data, sd_journal_enumerate_data, sd_journal_restart_data, SD_JOURNAL_FOREACH_DATA — Read data fields from the current journal entry
#include <systemd/sd-journal.h>
int sd_journal_get_data( | sd_journal* j, |
const char* field, | |
const void** data, | |
size_t* length) ; |
int sd_journal_enumerate_data( | sd_journal* j, |
const void** data, | |
size_t* length) ; |
int sd_journal_restart_data( | sd_journal* j) ; |
SD_JOURNAL_FOREACH_DATA( | sd_journal* j, |
const void* data, | |
size_t length) ; |
sd_journal_get_data()
gets
the data object associated with a specific field from
the current journal entry. It takes four arguments:
the journal context object, a string with the field
name to request, plus a pair of pointers to
pointer/size variables where the data object and its
size shall be stored in. The field name should be an
entry field name. Well-known field names are listed in
systemd.journal-fields(7). The
returned data is in a read-only memory map and is only
valid until the next invocation of
sd_journal_get_data()
or
sd_journal_enumerate_data()
, or
the read pointer is altered. Note that the data
returned will be prefixed with the field name and
'='.
sd_journal_enumerate_data()
may be used to iterate through all fields of the
current entry. On each invocation the data for the
next field is returned. The order of these fields is
not defined. The data returned is in the same format
as with sd_journal_get_data()
and
also follows the same life-time semantics.
sd_journal_restart_data()
resets the data enumeration index to the beginning of
the entry. The next invocation of
sd_journal_enumerate_data()
will return the first
field of the entry again.
Note that the
SD_JOURNAL_FOREACH_DATA()
macro
may be used as a wrapper around
sd_journal_restart_data()
and
sd_journal_enumerate_data()
.
Note that these functions will not work before sd_journal_next(3) (or related call) has been called at least once, in order to position the read pointer at a valid entry.
sd_journal_get_data()
returns 0 on success or a negative errno-style error
code. If the current entry does not include the
specified field -ENOENT is returned. If
sd_journal_next(3)
has not been called at least once -EADDRNOTAVAIL is
returned. sd_journal_enumerate_data()
returns a positive integer if the next field has been
read, 0 when no more fields are known, or a negative
errno-style error
code. sd_journal_restart_data()
returns nothing.
The sd_journal_get_data()
,
sd_journal_enumerate_data()
and
sd_journal_restart_data()
interfaces are available as shared library, which can
be compiled and linked to with the
libsystemd-journal
pkg-config(1)
file.
See
sd_journal_next(3)
for a complete example how to use
sd_journal_get_data()
.
Use the
SD_JOURNAL_FOREACH_DATA
macro to
iterate through all fields of the current journal
entry:
... int print_fields(sd_journal *j) { const void *data; size_t l; SD_JOURNAL_FOREACH_DATA(j, data, length) printf("%.*s\n", (int) length, data); } ...