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
Link: http://lkml.kernel.org/r/20141202120430.71979060@gandalf.local.home
Acked-by: Alexei Starovoitov <ast@plumgrid.com>
Suggested-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index 7a8c1528e141f871cc9047202f55b838e51c50f6..e6a33db8385622e238b016dc51d6d8442f7665cc 100644 (file)
--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -45,6 +45,7 @@ enum filter_op_ids
        OP_GT,
        OP_GE,
        OP_BAND,
+       OP_NOT,
        OP_NONE,
        OP_OPEN_PAREN,
 };
@@ -67,6 +68,7 @@ static struct filter_op filter_ops[] = {
        { OP_GT,        ">",            5 },
        { OP_GE,        ">=",           5 },
        { OP_BAND,      "&",            6 },
+       { OP_NOT,       "!",            6 },
        { OP_NONE,      "OP_NONE",      0 },
        { OP_OPEN_PAREN, "(",           0 },
 };
@@ -85,6 +87,7 @@ enum {
        FILT_ERR_MISSING_FIELD,
        FILT_ERR_INVALID_FILTER,
        FILT_ERR_IP_FIELD_ONLY,
+       FILT_ERR_ILLEGAL_NOT_OP,
 };
 
 static char *err_text[] = {
@@ -101,6 +104,7 @@ static char *err_text[] = {
        "Missing field name and/or value",
        "Meaningless filter expression",
        "Only 'ip' field is supported for function trace",
+       "Illegal use of '!'",
 };
 
 struct opstack_op {
@@ -139,6 +143,7 @@ struct pred_stack {
        int                     index;
 };
 
+/* If not of not match is equal to not of not, then it is a match */
 #define DEFINE_COMPARISON_PRED(type)                                   \
 static int filter_pred_##type(struct filter_pred *pred, void *event)   \
 {                                                                      \
@@ -166,7 +171,7 @@ 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 +1033,7 @@ 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 +1595,17 @@ static int replace_preds(struct ftrace_event_call *call,
                        continue;
                }
 
+               if (elt->op == OP_NOT) {
+                       if (!n_preds || operand1 || operand2) {
+                               parse_error(ps, FILT_ERR_ILLEGAL_NOT_OP, 0);
+                               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;