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tracing: Rewrite filter logic to be simpler and faster
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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
results.

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: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
rostedt committed Mar 14, 2018
1 parent 478325f commit 8076559
Showing 2 changed files with 1,054 additions and 1,272 deletions.
15 changes: 5 additions & 10 deletions kernel/trace/trace.h
Original file line number Diff line number Diff line change
@@ -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)
2,311 changes: 1,049 additions & 1,262 deletions kernel/trace/trace_events_filter.c

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