sd_journal_foreach_data(3) — Linux manual page


SD_JOURNAL_GET_DATA(3)       sd_journal_get_data      SD_JOURNAL_GET_DATA(3)

NAME         top

       sd_journal_get_data, sd_journal_enumerate_data,
       sd_journal_enumerate_available_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         top

       #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_enumerate_available_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);

DESCRIPTION         top

       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), but any field can be specified. The
       returned data is in a read-only memory map and is only valid until
       the next invocation of sd_journal_get_data(),
       sd_journal_enumerate_data(), sd_journal_enumerate_available_data(),
       or when 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_enumerate_available_data() is similar to
       sd_journal_enumerate_data(), but silently skips any fields which may
       be valid, but are too large or not supported by current

       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

       Note that the SD_JOURNAL_FOREACH_DATA() macro may be used as a handy
       wrapper around sd_journal_restart_data() and

       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 an 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 VALUE         top

       sd_journal_get_data() returns 0 on success or a negative errno-style
       error code.  sd_journal_enumerate_data() and
       sd_journal_enumerate_available_data() return a positive integer if
       the next field has been read, 0 when no more fields remain, or a
       negative errno-style error code.  sd_journal_restart_data() doesn't
       return anything.  sd_journal_set_data_threshold() and
       sd_journal_get_threshold() return 0 on success or a negative
       errno-style error code.

       Returned errors may indicate the following problems:

           One of the required parameters is NULL or invalid.

           The journal object was created in a different process.

           The read pointer is not positioned at a valid entry;
           sd_journal_next(3) or a related call has not been called at least

           The current entry does not include the specified field.

           Memory allocation failed.

           A compressed entry is too large.

           The data field is too large for this computer architecture (e.g.
           above 4 GB on a 32-bit architecture).

           The journal is compressed with an unsupported method or the
           journal uses an unsupported feature.

           The journal is corrupted (possibly just the entry being iterated

           An I/O error was reported by the kernel.

NOTES         top

       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.

EXAMPLES         top

       See sd_journal_next(3) for a complete example how to use

       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 ALSO         top

       systemd(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)

COLOPHON         top

       This page is part of the systemd (systemd system and service manager)
       project.  Information about the project can be found at 
       ⟨⟩.  If you have a bug
       report for this manual page, see
       ⟨⟩.  This
       page was obtained from the project's upstream Git repository
       ⟨⟩ on 2020-11-01.  (At that
       time, the date of the most recent commit that was found in the repos‐
       itory was 2020-11-01.)  If you discover any rendering problems in
       this HTML version of the page, or you believe there is a better or
       more up-to-date source for the page, or you have corrections or im‐
       provements to the information in this COLOPHON (which is not part of
       the original manual page), send a mail to

systemd 247                                           SD_JOURNAL_GET_DATA(3)