DNSTABLE_MERGE_FUNC(3)DNSTABLE_MERGE_FUNC(3)NAMEdnstable_merge_func - libmtbl merge function for dnstable key-value
entries
SYNOPSIS
#include <dnstable.h>
void
dnstable_merge_func(void *clos,
const uint8_t *key, size_t len_key,
const uint8_t *val0, size_t len_val0,
const uint8_t *val1, size_t len_val1,
uint8_t **merged_val, size_t *len_merged_val);
DESCRIPTION
This is the libmtbl merging function for dnstable key-value entries.
dnstable is built on libmtbl, and libmtbl requires a “merge function”
to resolve conflicting values between identical keys. The symbol
dnstable_merge_func can be provided to libmtbl functions requiring a
merge function when dealing with dnstable key-value data.
There are four dnstable MTBL key-value entry types. dnstable_merge_func
handles them in the following manner:
ENTRY_TYPE_RRSET_NAME_FWD and ENTRY_TYPE_RDATA_NAME_REV entries have no
associated value (that is, the values for these types is zero length).
A zero-length byte array is provided as the merged value.
ENTRY_TYPE_RRSET and ENTRY_TYPE_RDATA entries have an identical
encoding format. These types encode a triplet of varint-encoded
integers representing the time_first, time_last, and count value
fields. A new triplet of varint-encoded integers is generated as the
merged value as follows:
· The earliest (that is, smallest) of the two time_first values is
taken as the merged time_first value.
· The latest (that is, largest) of the two time_last values is taken
as the merged time_last value.
· The two count values are added together.
SEE ALSOdnstable-encoding(5), mtbl_merger(3)
11/10/2015 DNSTABLE_MERGE_FUNC(3)
