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Subject[PATCH] tracing: Add NOT to filtering logic

Ted noticed that he could not filter on an event for a bit being cleared.
That's because the filtering logic only tests event fields with a limited
number of comparisons which, for bit logic, only include "&", which can
test if a bit is set, but there's no good way to see if a bit is clear.

This adds a way to do: !(field & 2048)

Which returns true if the bit is not set, and false otherwise.

Note, currently !(field1 == 10 && field2 == 15) is not supported.
That is, the 'not' only works for direct comparisons, not for the
AND and OR logic.

Link: http://lkml.kernel.org/r/20141202021912.GA29096@thunk.org

Suggested-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
kernel/trace/trace_events_filter.c | 16 ++++++++++++++--
1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index 7a8c1528e141..9ddbf0c05340 100644
--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -37,6 +37,7 @@ enum filter_op_ids
{
OP_OR,
OP_AND,
+ OP_NOT,
OP_GLOB,
OP_NE,
OP_EQ,
@@ -59,6 +60,7 @@ struct filter_op {
static struct filter_op filter_ops[] = {
{ OP_OR, "||", 1 },
{ OP_AND, "&&", 2 },
+ { OP_NOT, "!", 3 },
{ OP_GLOB, "~", 4 },
{ OP_NE, "!=", 4 },
{ OP_EQ, "==", 4 },
@@ -166,7 +168,7 @@ static int filter_pred_##type(struct filter_pred *pred, void *event) \
break; \
} \
\
- return match; \
+ return match == !pred->not; \
}

#define DEFINE_EQUALITY_PRED(size) \
@@ -1028,7 +1030,7 @@ static int init_pred(struct filter_parse_state *ps,
}

if (pred->op == OP_NE)
- pred->not = 1;
+ pred->not ^= 1;

pred->fn = fn;
return 0;
@@ -1590,6 +1592,16 @@ static int replace_preds(struct ftrace_event_call *call,
continue;
}

+ if (elt->op == OP_NOT) {
+ if (!n_preds) {
+ err = -EINVAL;
+ goto fail;
+ }
+ if (!dry_run)
+ filter->preds[n_preds - 1].not ^= 1;
+ continue;
+ }
+
if (WARN_ON(n_preds++ == MAX_FILTER_PRED)) {
parse_error(ps, FILT_ERR_TOO_MANY_PREDS, 0);
err = -ENOSPC;
--
1.8.1.4


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