bus: rework bloom filter logic to operate with variable bloom filter

sizes and numbers of hash functions

In order to make the bloom filter logic more future proof communicate
bloom filter parameters from the original bus creator to the clients,
and allow them to be variable within certain ranges.

1 files changed, 18 insertions, 4 deletions

diff --git a/src/libsystemd/sd-bus/bus-bloom.h b/src/libsystemd/sd-bus/bus-bloom.h
index 422eb4e01..0dad5db78 100644
--- a/src/libsystemd/sd-bus/bus-bloom.h
+++ b/src/libsystemd/sd-bus/bus-bloom.h
@@ -23,7 +23,21 @@
 
 #include <sys/types.h>
 
-#define BLOOM_SIZE 64
-
-void bloom_add_pair(uint64_t filter[BLOOM_SIZE/8], const char *a, const char *b);
-void bloom_add_prefixes(uint64_t filter[BLOOM_SIZE/8], const char *a, const char *b, char sep);
+/*
+ * Our default bloom filter has the following parameters:
+ *
+ * m=512   (bits in the filter)
+ * k=8     (hash functions)
+ *
+ * We use SipHash24 as hash function with a number of (originally
+ * randomized) but fixed hash keys.
+ *
+ */
+
+#define DEFAULT_BLOOM_SIZE (512/8) /* m: filter size */
+#define DEFAULT_BLOOM_N_HASH 8     /* k: number of hash functions */
+
+void bloom_add_pair(uint64_t filter[], size_t size, unsigned n_hash, const char *a, const char *b);
+void bloom_add_prefixes(uint64_t filter[], size_t size, unsigned n_hash, const char *a, const char *b, char sep);
+
+bool bloom_validate_parameters(size_t size, unsigned n_hash);