[DTrace-devel] [PATCH 2/6] bpf: add agggen handling to get_agg()

[Kris Van Hees]

The get_agg() function will now consult the generation value for the
aggregation id.  If existing data is of an earlier generation, the
data is reset.

Signed-off-by: Kris Van Hees <kris.van.hees at oracle.com>
---
 bpf/get_agg.c | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/bpf/get_agg.c b/bpf/get_agg.c
index aba8a229..37ac420e 100644
--- a/bpf/get_agg.c
+++ b/bpf/get_agg.c
@@ -11,6 +11,8 @@
 # define noinline	__attribute__((noinline))
 #endif
 
+extern struct bpf_map_def agggen;
+
 /*
  * Get a pointer to the data storage for an aggregation.  Regular aggregations
  * are stored as an indexed aggregation with an empty key.  The 'id' parameter
@@ -21,16 +23,22 @@
 noinline uint64_t *dt_get_agg(const dt_dctx_t *dctx, uint32_t id,
 			      const char *key, uint64_t ival, const char *dflt)
 {
+	uint64_t	*genp;
 	uint64_t	*valp;
 
+	/* get the gen value */
+	genp = bpf_map_lookup_elem(&agggen, &id);
+	if (genp == 0)
+		return 0;
+
 	/* place the variable ID at the beginning of the key */
 	*(uint32_t *)key = id;
 
 	/* try to look up the key */
 	valp = bpf_map_lookup_elem(dctx->agg, key);
 
-	/* if not found, create it */
-	if (valp == 0) {
+	/* if not found, or older gen, set initial values */
+	if (valp == 0 || valp[0] < *genp) {
 		/* start with all zeroes */
 		if (bpf_map_update_elem(dctx->agg, key, dflt, BPF_ANY) < 0)
 			return 0;
@@ -42,10 +50,10 @@ noinline uint64_t *dt_get_agg(const dt_dctx_t *dctx, uint32_t id,
 		/* ival is nonzero only for min() and max() */
 		if (ival)
 			valp[1] = ival;
-	}
 
-	/* increment the data counter */
-	valp[0] += 1;
+		/* set the gen value */
+		valp[0] = *genp;
+	}
 
 	/* advance past the data counter */
 	valp += 1;
-- 
2.39.1