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Subject[PATCH 2/3 v2] tracing: Clean up and document pred_funcs_##type creation and use
From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>

The pred_funcs_##type arrays consist of five functions that are assigned
based on the ops. The array must be in the same order of the ops each
function represents. The PRED_FUNC_START macro denotes the op enum that
starts the op that maps to the pred_funcs_##type arrays. This is all very
subtle and prone to bugs if the code is changed.

Add comments describing how PRED_FUNC_START and pred_funcs_##type array is
used, and also a PRED_FUNC_MAX that is the maximum number of functions in
the arrays.

Clean up select_comparison_fn() that assigns the predicates to the
pred_funcs_##type array function as well as add protection in case an op is
passed in that does not map correctly to the array.

Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
kernel/trace/trace_events_filter.c | 46 ++++++++++++++++++++++++++------------
1 file changed, 32 insertions(+), 14 deletions(-)

diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index a2ef393b3bb2..9d383f4383dc 100644
--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -65,6 +65,13 @@ struct filter_op {

static struct filter_op filter_ops[] = { OPS };

+/*
+ * pred functions are OP_LT, OP_LE, OP_GT, OP_GE, and OP_BAND
+ * pred_funcs_##type below must match the order of them above.
+ */
+#define PRED_FUNC_START OP_LT
+#define PRED_FUNC_MAX (OP_BAND - PRED_FUNC_START)
+
#define ERRORS \
C( NONE, "No error"), \
C( INVALID_OP, "Invalid operator"), \
@@ -172,8 +179,6 @@ static const filter_pred_fn_t pred_funcs_##type[] = { \
filter_pred_BAND_##type, \
};

-#define PRED_FUNC_START OP_LT
-
#define DEFINE_EQUALITY_PRED(size) \
static int filter_pred_##size(struct filter_pred *pred, void *event) \
{ \
@@ -946,39 +951,52 @@ static filter_pred_fn_t select_comparison_fn(enum filter_op_ids op,
int field_size, int field_is_signed)
{
filter_pred_fn_t fn = NULL;
+ int pred_func_index = -1;
+
+ switch (op) {
+ case OP_EQ:
+ case OP_NE:
+ break;
+ default:
+ if (WARN_ON_ONCE(op < PRED_FUNC_START))
+ return NULL;
+ pred_func_index = op - PRED_FUNC_START;
+ if (WARN_ON_ONCE(pred_func_index > PRED_FUNC_MAX))
+ return NULL;
+ }

switch (field_size) {
case 8:
- if (op == OP_EQ || op == OP_NE)
+ if (pred_func_index < 0)
fn = filter_pred_64;
else if (field_is_signed)
- fn = pred_funcs_s64[op - PRED_FUNC_START];
+ fn = pred_funcs_s64[pred_func_index];
else
- fn = pred_funcs_u64[op - PRED_FUNC_START];
+ fn = pred_funcs_u64[pred_func_index];
break;
case 4:
- if (op == OP_EQ || op == OP_NE)
+ if (pred_func_index < 0)
fn = filter_pred_32;
else if (field_is_signed)
- fn = pred_funcs_s32[op - PRED_FUNC_START];
+ fn = pred_funcs_s32[pred_func_index];
else
- fn = pred_funcs_u32[op - PRED_FUNC_START];
+ fn = pred_funcs_u32[pred_func_index];
break;
case 2:
- if (op == OP_EQ || op == OP_NE)
+ if (pred_func_index < 0)
fn = filter_pred_16;
else if (field_is_signed)
- fn = pred_funcs_s16[op - PRED_FUNC_START];
+ fn = pred_funcs_s16[pred_func_index];
else
- fn = pred_funcs_u16[op - PRED_FUNC_START];
+ fn = pred_funcs_u16[pred_func_index];
break;
case 1:
- if (op == OP_EQ || op == OP_NE)
+ if (pred_func_index < 0)
fn = filter_pred_8;
else if (field_is_signed)
- fn = pred_funcs_s8[op - PRED_FUNC_START];
+ fn = pred_funcs_s8[pred_func_index];
else
- fn = pred_funcs_u8[op - PRED_FUNC_START];
+ fn = pred_funcs_u8[pred_func_index];
break;
}

--
2.15.1

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