Ubuntu Manpage: sd_journal_get_data, sd_journal_enumerate_data, sd_journal_enumerate_available

Provided by: libsystemd-dev_256.5-2ubuntu4_amd64

NAME

       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

       #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

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 implementation.

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_available_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 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

       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.

   Errors
       Returned errors may indicate the following problems:

       -EINVAL
           One of the required parameters is NULL or invalid.

           Added in version 246.

       -ECHILD
           The journal object was created in a different process, library or module instance.

           Added in version 246.

       -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.

           Added in version 246.

       -ENOENT
           The current entry does not include the specified field.

           Added in version 246.

       -ENOMEM
           Memory allocation failed.

           Added in version 246.

       -ENOBUFS
           A compressed entry is too large.

           Added in version 246.

       -E2BIG
           The data field is too large for this computer architecture (e.g. above 4 GB on a
           32-bit architecture).

           Added in version 246.

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

           Added in version 246.

       -EBADMSG
           The journal is corrupted (possibly just the entry being iterated over).

           Added in version 246.

       -EIO
           An I/O error was reported by the kernel.

           Added in version 246.

NOTES

       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.

       Functions described here are available as a shared library, which can be compiled against
       and linked to with the libsystemd 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);
           }
           ...

HISTORY

       sd_journal_get_data(), sd_journal_enumerate_data(), sd_journal_restart_data(), and
       SD_JOURNAL_FOREACH_DATA() were added in version 187.

       sd_journal_set_data_threshold() and sd_journal_get_data_threshold() were added in version
       196.

       sd_journal_enumerate_available_data() was added in version 246.