SD_JOURNAL_GET_DATA(3)sd_journal_get_dataSD_JOURNAL_GET_DATA(3)NAME
sd_journal_get_data, sd_journal_enumerate_data,
sd_journal_restart_data, SD_JOURNAL_FOREACH_DATA,
sd_journal_set_data_threshold, sd_journal_get_data_threshold - Read
data fields from the current journal entry
SYNOPSIS
#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);
void sd_journal_restart_data(sd_journal* j);
SD_JOURNAL_FOREACH_DATA(sd_journal* j, const void* data,
size_t length);
int sd_journal_set_data_threshold(sd_journal* j, size_t sz);
int sd_journal_get_data_threshold(sd_journal* j, size_t* sz);
DESCRIPTIONsd_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 '='. Also
note that by default data fields larger than 64K might get truncated to
64K. This threshold may be changed and turned off with
sd_journal_set_data_threshold() (see below).
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 handy
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_set_data_threshold() may be used to change the data field
size threshold for data returned by sd_journal_get_data(),
sd_journal_enumerate_data() and sd_journal_enumerate_unique(). This
threshold is a hint only: it indicates that the client program is
interested only in the initial parts of the data fields, up to the
threshold in size -- but the library might still return larger data
objects. That means applications should not rely exclusively on this
setting to limit the size of the data fields returned, but need to
apply a explicit size limit on the returned data as well. This
threshold defaults to 64K by default. To retrieve the complete data
fields this threshold should be turned off by setting it to 0, so that
the library always returns the complete data objects. It is recommended
to set this threshold as low as possible since this relieves the
library from having to decompress large compressed data objects in
full.
sd_journal_get_data_threshold() returns the currently configured data
field size threshold.
RETURN VALUEsd_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.
sd_journal_set_data_threshold() and sd_journal_get_threshold() return 0
on success or a negative errno-style error code.
NOTES
The sd_journal_get_data(), sd_journal_enumerate_data(),
sd_journal_restart_data(), sd_journal_set_data_threshold() and
sd_journal_get_data_threshold() interfaces are available as a shared
library, which can be compiled and linked to with the
libsystemd-journal pkg-config(1) file.
EXAMPLES
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 length;
SD_JOURNAL_FOREACH_DATA(j, data, length)
printf("%.*s\n", (int) length, data);
}
...
SEE ALSOsystemd(1), systemd.journal-fields(7), sd-journal(3),
sd_journal_open(3), sd_journal_next(3),
sd_journal_get_realtime_usec(3), sd_journal_query_unique(3)systemd 208SD_JOURNAL_GET_DATA(3)
