чтение уникальных полей данных из журнала (read unique data fields from the journal)
Имя (Name)
sd_journal_query_unique, sd_journal_enumerate_unique,
sd_journal_enumerate_available_unique, sd_journal_restart_unique,
SD_JOURNAL_FOREACH_UNIQUE - Read unique data fields from the
journal
Синопсис (Synopsis)
#include <systemd/sd-journal.h>
int sd_journal_query_unique(sd_journal *j, const char *field);
int sd_journal_enumerate_available_unique(sd_journal *j,
const void **data,
size_t *length);
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);
Описание (Description)
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), but any field can
be specified. 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() and
sd_journal_enumerate_available_unique(). Invoking one of those
calls 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 object, plus a pair of pointers to pointer/size
variables where the data object and its size shall be stored. 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() and
only the initial part of the field up to the threshold is
returned. An error is returned for fields which cannot be
retrieved. See the error list below for details.
sd_journal_enumerate_available_unique() is similar to
sd_journal_enumerate_unique(), but silently skips any fields
which may be valid, but are too large or not supported by current
implementation.
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_available_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.
Возвращаемое значение (Return value)
sd_journal_query_unique() returns 0 on success or a negative
errno-style error code. sd_journal_enumerate_unique() and
sd_journal_query_available_unique() return a positive integer if
the next field data has been read, 0 when no more fields remain,
or a negative errno-style error code.
sd_journal_restart_unique() doesn't return anything.
Errors
Returned errors may indicate the following problems:
-EINVAL
One of the required parameters is NULL or invalid.
-ECHILD
The journal object was created in a different process.
-EADDRNOTAVAIL
The read pointer is not positioned at a valid entry;
sd_journal_next(3) or a related call has not been called at
least once.
-ENOENT
The current entry does not include the specified field.
-ENOBUFS
A compressed entry is too large.
-E2BIG
The data field is too large for this computer architecture
(e.g. above 4 GB on a 32-bit architecture).
-EPROTONOSUPPORT
The journal is compressed with an unsupported method or the
journal uses an unsupported feature.
-EBADMSG
The journal is corrupted (possibly just the entry being
iterated over).
-EIO
An I/O error was reported by the kernel.
Примечание (Note)
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.
Примеры (Examples)
Use the SD_JOURNAL_FOREACH_UNIQUE() macro to iterate through all
values a field of the journal can take (and which can be accessed
on the given architecture and are not compressed with an
unsupported mechanism). 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;
}
Смотри также (See also)
systemd(1), systemd.journal-fields(7), sd-journal(3),
sd_journal_open(3), sd_journal_enumerate_fields(3),
sd_journal_get_data(3), sd_journal_add_match(3)
