[DTrace-devel] [PATCH 1/6] bpf: add 'agggen' BPF map

[Kris Van Hees]

The 'agggen' BPF map associates a generation counter with an aggregation
ID.  It will be used to determine whether the aggregation data in the
'aggs' map for aggregations associated with a given aggregation ID is
valid or stale.

The initial generation counter for each aggregation is 1 (because 0 is
used to indicate a no-data condition).

Signed-off-by: Kris Van Hees <kris.van.hees at oracle.com>
---
 libdtrace/dt_bpf.c                  | 38 +++++++++++++++++++++++------
 libdtrace/dt_dlibs.c                |  1 +
 libdtrace/dt_impl.h                 |  1 +
 test/stress/buffering/err.resize2.r |  2 +-
 4 files changed, 33 insertions(+), 9 deletions(-)

diff --git a/libdtrace/dt_bpf.c b/libdtrace/dt_bpf.c
index f0f46c5c..6587ea95 100644
--- a/libdtrace/dt_bpf.c
+++ b/libdtrace/dt_bpf.c
@@ -477,18 +477,23 @@ gmap_create_state(dtrace_hdl_t *dtp)
 }
 
 /*
- * Create the 'aggs' BPF map.
+ * Create the 'aggs' BPF map (and its companion 'agggen' BPF map).
  *
- * Aggregation data buffer map, associated with each CPU.  The map is
- * implemented as a global array-of-maps indexed by CPU id.  The associated
- * value is a map with a singleton element (key 0).
+ * - aggs:	Aggregation data buffer map, associated with each CPU.  The map
+ *		is implemented as a global array-of-maps indexed by CPU id.
+ *		The associated value is a map with a singleton element (key 0).
+ * - agggen:	Aggregation generation counters.  The map associates a
+ *		generation counter with each aggregation ID.  The counter is
+ *		used to determine whether the aggregation data is valid.  The
+ *		initial value is 1.
  */
 static int
 gmap_create_aggs(dtrace_hdl_t *dtp)
 {
-	size_t	ncpus = dtp->dt_conf.max_cpuid + 1;
-	size_t	nelems = 0;
-	int	i;
+	size_t		ncpus = dtp->dt_conf.max_cpuid + 1;
+	size_t		nelems = 0;
+	uint32_t	aggc =  dt_idhash_peekid(dtp->dt_aggs);
+	uint32_t	i;
 
 	/* Only create the map if it is used. */
 	if (dtp->dt_maxaggdsize == 0)
@@ -508,6 +513,8 @@ gmap_create_aggs(dtrace_hdl_t *dtp)
 						BPF_MAP_TYPE_HASH,
 						dtp->dt_maxtuplesize,
 						dtp->dt_maxaggdsize, nelems);
+	if (dtp->dt_aggmap_fd == -1)
+		return -1;
 
 	for (i = 0; i < dtp->dt_conf.num_online_cpus; i++) {
 		int	cpu = dtp->dt_conf.cpus[i].cpu_id;
@@ -524,8 +531,23 @@ gmap_create_aggs(dtrace_hdl_t *dtp)
 		dt_bpf_map_update(dtp->dt_aggmap_fd, &cpu, &fd);
 	}
 
+	/* Create the agg generation value array. */
+	dtp->dt_genmap_fd = create_gmap(dtp, "agggen", BPF_MAP_TYPE_ARRAY,
+					sizeof(uint32_t), sizeof(uint64_t),
+					aggc);
+	if (dtp->dt_genmap_fd == -1)
+		 return -1;
+
+	for (i = 0; i < aggc; i++) {
+		uint64_t	val = 1;
 
-	return dtp->dt_aggmap_fd;
+		if (dt_bpf_map_update(dtp->dt_genmap_fd, &i, &val) == -1)
+			return dt_bpf_error(dtp,
+					    "cannot update BPF map 'agggen': %s\n",
+					    strerror(errno));
+	}
+
+	return 0;
 }
 
 /*
diff --git a/libdtrace/dt_dlibs.c b/libdtrace/dt_dlibs.c
index c302b19c..eea0ba41 100644
--- a/libdtrace/dt_dlibs.c
+++ b/libdtrace/dt_dlibs.c
@@ -57,6 +57,7 @@ static const dt_ident_t		dt_bpf_symbols[] = {
 
 	/* BPF maps */
 	DT_BPF_SYMBOL(aggs, DT_IDENT_PTR),
+	DT_BPF_SYMBOL(agggen, DT_IDENT_PTR),
 	DT_BPF_SYMBOL(buffers, DT_IDENT_PTR),
 	DT_BPF_SYMBOL(cpuinfo, DT_IDENT_PTR),
 	DT_BPF_SYMBOL(dvars, DT_IDENT_PTR),
diff --git a/libdtrace/dt_impl.h b/libdtrace/dt_impl.h
index 3e14d69d..32b0c923 100644
--- a/libdtrace/dt_impl.h
+++ b/libdtrace/dt_impl.h
@@ -380,6 +380,7 @@ struct dtrace_hdl {
 	int dt_proc_fd;		/* file descriptor for proc eventfd */
 	int dt_stmap_fd;	/* file descriptor for the 'state' BPF map */
 	int dt_aggmap_fd;	/* file descriptor for the 'aggs' BPF map */
+	int dt_genmap_fd;	/* file descriptor for the 'agggen' BPF map */
 	dtrace_handle_err_f *dt_errhdlr; /* error handler, if any */
 	void *dt_errarg;	/* error handler argument */
 	dtrace_handle_drop_f *dt_drophdlr; /* drop handler, if any */
diff --git a/test/stress/buffering/err.resize2.r b/test/stress/buffering/err.resize2.r
index a4fbe390..2b5728ca 100644
--- a/test/stress/buffering/err.resize2.r
+++ b/test/stress/buffering/err.resize2.r
@@ -1,3 +1,3 @@
 -- @@stderr --
 dtrace: script 'test/stress/buffering/err.resize2.d' matched 1 probe
-dtrace: could not enable tracing: failed to create BPF map 'aggs_0': Too big
+dtrace: could not enable tracing: failed to create BPF map 'aggs': Too big
-- 
2.39.1