Commit 80765597 authored by Steven Rostedt (VMware)'s avatar Steven Rostedt (VMware)
Browse files

tracing: Rewrite filter logic to be simpler and faster

Al Viro reviewed the filter logic of ftrace trace events and found it to be
very troubling. It creates a binary tree based on the logic operators and
walks it during tracing. He sent myself and Tom Zanussi a long explanation
(and formal proof) of how to do the string parsing better and end up with a
program array that can be simply iterated to come up with the correct

I took his ideas and his pseudo code and rewrote the filter logic based on
them. In doing so, I was able to remove a lot of code, and have a much more
condensed filter logic in the process. I wrote a very long comment
describing the methadology that Al proposed in my own words. For more info
on how this works, read the comment above predicate_parse().
Suggested-by: default avatarAl Viro <>
Signed-off-by: default avatarSteven Rostedt (VMware) <>
parent 478325f1
......@@ -1216,12 +1216,11 @@ struct ftrace_event_field {
int is_signed;
struct prog_entry;
struct event_filter {
int n_preds; /* Number assigned */
int a_preds; /* allocated */
struct filter_pred __rcu *preds;
struct filter_pred __rcu *root;
char *filter_string;
struct prog_entry __rcu *prog;
char *filter_string;
struct event_subsystem {
......@@ -1413,12 +1412,8 @@ struct filter_pred {
unsigned short *ops;
struct ftrace_event_field *field;
int offset;
int not;
int not;
int op;
unsigned short index;
unsigned short parent;
unsigned short left;
unsigned short right;
static inline bool is_string_field(struct ftrace_event_field *field)
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