[PATCH nft 3/4] src: cache result of time() during parsing/output

[Thomas Haller <thaller@xxxxxxxxxx>]

When we parse/output a larger set of data, we should only call time()
once. With every call of time(), the value keeps ticking (and is subject
to time reset). Previously, one parse/output operation will make
decisions on potentially different timestamps.

Add a cache to the parse/output context, and only fetch time() once
per operation.

Signed-off-by: Thomas Haller <thaller@xxxxxxxxxx>
---
 include/datatype.h |  6 ++++++
 src/datatype.c     | 16 ++++++++++++++++
 src/meta.c         |  4 ++--
 3 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/include/datatype.h b/include/datatype.h
index 79d996edd348..abd093765703 100644
--- a/include/datatype.h
+++ b/include/datatype.h
@@ -2,6 +2,7 @@
 #define NFTABLES_DATATYPE_H
 
 #include <json.h>
+#include <time.h>
 
 /**
  * enum datatypes
@@ -121,12 +122,17 @@ enum byteorder {
 struct expr;
 
 struct ops_cache {
+	time_t		time;
+	bool		has_time;
 };
 
 #define CTX_CACHE_INIT() \
 	{ \
+		.has_time = false, \
 	}
 
+extern time_t ops_cache_get_time(struct ops_cache *cache);
+
 /**
  * enum datatype_flags
  *
diff --git a/src/datatype.c b/src/datatype.c
index dd6a5fbf5df8..933d832c4f4d 100644
--- a/src/datatype.c
+++ b/src/datatype.c
@@ -35,6 +35,22 @@
 
 #include <netinet/ip_icmp.h>
 
+time_t ops_cache_get_time(struct ops_cache *cache)
+{
+	time_t t;
+
+	if (!cache || !cache->has_time) {
+		t = time(NULL);
+		if (cache) {
+			cache->has_time = true;
+			cache->time = time(NULL);
+		}
+	} else
+		t = cache->time;
+
+	return t;
+}
+
 static const struct datatype *datatypes[TYPE_MAX + 1] = {
 	[TYPE_INVALID]		= &invalid_type,
 	[TYPE_VERDICT]		= &verdict_type,
diff --git a/src/meta.c b/src/meta.c
index 4f383269d032..1d853b219fe6 100644
--- a/src/meta.c
+++ b/src/meta.c
@@ -496,7 +496,7 @@ static void hour_type_print(const struct expr *expr, struct output_ctx *octx)
 	time_t ts;
 
 	/* Obtain current tm, so that we can add tm_gmtoff */
-	ts = time(NULL);
+	ts = ops_cache_get_time(octx->ops_cache);
 	if (ts != ((time_t) -1) && localtime_r(&ts, &cur_tm))
 		seconds = (seconds + cur_tm.tm_gmtoff) % SECONDS_PER_DAY;
 
@@ -534,7 +534,7 @@ static struct error_record *hour_type_parse(struct parse_ctx *ctx,
 	result = 0;
 
 	/* Obtain current tm, so that we can substract tm_gmtoff */
-	ts = time(NULL);
+	ts = ops_cache_get_time(ctx->ops_cache);
 	if (ts != ((time_t) -1) && localtime_r(&ts, &cur_tm_data))
 		cur_tm = &cur_tm_data;
 	else
-- 
2.41.0