sd_journal_get_data.3 6.5 KB
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.TH "SD_JOURNAL_GET_DATA" "3" "" "systemd 215" "sd_journal_get_data"
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.nh
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.\" * MAIN CONTENT STARTS HERE *
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.SH "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
.SH "SYNOPSIS"
.sp
.ft B
.nf
#include <systemd/sd\-journal\&.h>
.fi
.ft
.HP \w'int\ sd_journal_get_data('u
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.BI "int sd_journal_get_data(sd_journal\ *" "j" ", const\ char\ *" "field" ", const\ void\ **" "data" ", size_t\ *" "length" ");"
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.HP \w'int\ sd_journal_enumerate_data('u
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.BI "int sd_journal_enumerate_data(sd_journal\ *" "j" ", const\ void\ **" "data" ", size_t\ *" "length" ");"
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.HP \w'void\ sd_journal_restart_data('u
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.BI "void sd_journal_restart_data(sd_journal\ *" "j" ");"
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.HP \w'SD_JOURNAL_FOREACH_DATA('u
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.BI "SD_JOURNAL_FOREACH_DATA(sd_journal\ *" "j" ", const\ void\ *" "data" ", size_t\ " "length" ");"
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.HP \w'int\ sd_journal_set_data_threshold('u
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.BI "int sd_journal_set_data_threshold(sd_journal\ *" "j" ", size_t\ " "sz" ");"
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.HP \w'int\ sd_journal_get_data_threshold('u
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.BI "int sd_journal_get_data_threshold(sd_journal\ *" "j" ", size_t\ *" "sz" ");"
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.SH "DESCRIPTION"
.PP
\fBsd_journal_get_data()\fR
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
\fBsystemd.journal-fields\fR(7)\&. The returned data is in a read\-only memory map and is only valid until the next invocation of
\fBsd_journal_get_data()\fR
or
\fBsd_journal_enumerate_data()\fR, or the read pointer is altered\&. Note that the data returned will be prefixed with the field name and \*(Aq=\*(Aq\&. Also note that by default data fields larger than 64K might get truncated to 64K\&. This threshold may be changed and turned off with
\fBsd_journal_set_data_threshold()\fR
(see below)\&.
.PP
\fBsd_journal_enumerate_data()\fR
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
\fBsd_journal_get_data()\fR
and also follows the same life\-time semantics\&.
.PP
\fBsd_journal_restart_data()\fR
resets the data enumeration index to the beginning of the entry\&. The next invocation of
\fBsd_journal_enumerate_data()\fR
will return the first field of the entry again\&.
.PP
Note that the
\fBSD_JOURNAL_FOREACH_DATA()\fR
macro may be used as a handy wrapper around
\fBsd_journal_restart_data()\fR
and
\fBsd_journal_enumerate_data()\fR\&.
.PP
Note that these functions will not work before
\fBsd_journal_next\fR(3)
(or related call) has been called at least once, in order to position the read pointer at a valid entry\&.
.PP
\fBsd_journal_set_data_threshold()\fR
may be used to change the data field size threshold for data returned by
\fBsd_journal_get_data()\fR,
\fBsd_journal_enumerate_data()\fR
and
\fBsd_journal_enumerate_unique()\fR\&. 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\&.
.PP
\fBsd_journal_get_data_threshold()\fR
returns the currently configured data field size threshold\&.
.SH "RETURN VALUE"
.PP
\fBsd_journal_get_data()\fR
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
\fBsd_journal_next\fR(3)
has not been called at least once, \-EADDRNOTAVAIL is returned\&.
\fBsd_journal_enumerate_data()\fR
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\&.
\fBsd_journal_restart_data()\fR
returns nothing\&.
\fBsd_journal_set_data_threshold()\fR
and
\fBsd_journal_get_threshold()\fR
return 0 on success or a negative errno\-style error code\&.
.SH "NOTES"
.PP
The
\fBsd_journal_get_data()\fR,
\fBsd_journal_enumerate_data()\fR,
\fBsd_journal_restart_data()\fR,
\fBsd_journal_set_data_threshold()\fR
and
\fBsd_journal_get_data_threshold()\fR
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interfaces are available as a shared library, which can be compiled and linked to with the
\fBlibsystemd\fR\ \&\fBpkg-config\fR(1)
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file\&.
.SH "EXAMPLES"
.PP
See
\fBsd_journal_next\fR(3)
for a complete example how to use
\fBsd_journal_get_data()\fR\&.
.PP
Use the
\fBSD_JOURNAL_FOREACH_DATA\fR
macro to iterate through all fields of the current journal entry:
.sp
.if n \{\
.RS 4
.\}
.nf
\&.\&.\&.
int print_fields(sd_journal *j) {
        const void *data;
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        size_t length;
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        SD_JOURNAL_FOREACH_DATA(j, data, length)
                printf("%\&.*s\en", (int) length, data);
}
\&.\&.\&.
.fi
.if n \{\
.RE
.\}
.SH "SEE ALSO"
.PP
\fBsystemd\fR(1),
\fBsystemd.journal-fields\fR(7),
\fBsd-journal\fR(3),
\fBsd_journal_open\fR(3),
\fBsd_journal_next\fR(3),
\fBsd_journal_get_realtime_usec\fR(3),
\fBsd_journal_query_unique\fR(3)