[RFC][PATCH v2 5/7] trace: make filter_parse_regex() provide the length of substring to compare with

[Al Viro]

From: Al Viro <viro@xxxxxxxxxxxxxxxxxx>

	By this point the only thing that cares about
NUL-termination of substring found by filter_parse_regex() is
strlen() done immediately by all its callers.  Once we have found
the length, that's it - we won't be looking at more than that
many bytes in the substring in question.

	This commit consolidates those strlen() calls into one
done by filter_parse_regex() itself.  To report the length to the
callers, we switch to passing 'len' argument of filter_parse_regex()
by address and use it to pass the length of our substring on the
way out.

	The next commit will eliminate modifying the string
completely - filter_parse_regex() has enough information to find
the length of the substring without bothering with this strlen()
call.

Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
---
 kernel/trace/ftrace.c              | 24 +++++++++---------------
 kernel/trace/trace.h               |  2 +-
 kernel/trace/trace_events_filter.c | 10 +++++-----
 3 files changed, 15 insertions(+), 21 deletions(-)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index a369a54..f640458 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -3441,7 +3441,6 @@ static int
 match_records(struct ftrace_hash *hash, char *buff,
 	      int len, char *mod, int not)
 {
-	unsigned search_len = 0;
 	struct ftrace_page *pg;
 	struct dyn_ftrace *rec;
 	int type = MATCH_FULL;
@@ -3449,10 +3448,8 @@ match_records(struct ftrace_hash *hash, char *buff,
 	int found = 0;
 	int ret;
 
-	if (len) {
-		type = filter_parse_regex(buff, len, &search, &not);
-		search_len = strlen(search);
-	}
+	if (len)
+		type = filter_parse_regex(buff, &len, &search, &not);
 
 	mutex_lock(&ftrace_lock);
 
@@ -3460,7 +3457,7 @@ match_records(struct ftrace_hash *hash, char *buff,
 		goto out_unlock;
 
 	do_for_each_ftrace_rec(pg, rec) {
-		if (ftrace_match_record(rec, mod, search, search_len, type)) {
+		if (ftrace_match_record(rec, mod, search, len, type)) {
 			ret = enter_record(hash, rec, not);
 			if (ret < 0) {
 				found = ret;
@@ -3648,14 +3645,13 @@ register_ftrace_function_probe(char *glob, struct ftrace_probe_ops *ops,
 	struct ftrace_hash *hash;
 	struct ftrace_page *pg;
 	struct dyn_ftrace *rec;
-	int type, len, not;
+	int type, len = strlen(glob), not;
 	unsigned long key;
 	int count = 0;
 	char *search;
 	int ret;
 
-	type = filter_parse_regex(glob, strlen(glob), &search, &not);
-	len = strlen(search);
+	type = filter_parse_regex(glob, &len, &search, &not);
 
 	/* we do not support '!' for function probes */
 	if (WARN_ON(not))
@@ -3768,9 +3764,9 @@ __unregister_ftrace_function_probe(char *glob, struct ftrace_probe_ops *ops,
 
 	if (glob && *glob && strcmp(glob, "*") != 0) {
 		int not;
+		len = strlen(glob);
 
-		type = filter_parse_regex(glob, strlen(glob), &search, &not);
-		len = strlen(search);
+		type = filter_parse_regex(glob, &len, &search, &not);
 
 		/* we do not support '!' for function probes */
 		if (WARN_ON(not))
@@ -4549,7 +4545,7 @@ ftrace_set_func(unsigned long *array, int *idx, int size, char *buffer)
 {
 	struct dyn_ftrace *rec;
 	struct ftrace_page *pg;
-	int search_len;
+	int search_len = strlen(buffer);
 	int fail = 1;
 	int type, not;
 	char *search;
@@ -4557,12 +4553,10 @@ ftrace_set_func(unsigned long *array, int *idx, int size, char *buffer)
 	int i;
 
 	/* decode regex */
-	type = filter_parse_regex(buffer, strlen(buffer), &search, &not);
+	type = filter_parse_regex(buffer, &search_len, &search, &not);
 	if (!not && *idx >= size)
 		return -EBUSY;
 
-	search_len = strlen(search);
-
 	mutex_lock(&ftrace_lock);
 
 	if (unlikely(ftrace_disabled)) {
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 8de48ba..7483205 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -1051,7 +1051,7 @@ struct filter_pred {
 };
 
 extern enum regex_type
-filter_parse_regex(char *buff, int len, char **search, int *not);
+filter_parse_regex(char *buff, int *len, char **search, int *not);
 extern void print_event_filter(struct ftrace_event_file *file,
 			       struct trace_seq *s);
 extern int apply_event_filter(struct ftrace_event_file *file,
diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index 6c4a96b..6a659e1 100644
--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -321,7 +321,7 @@ static int regex_match_end(char *str, struct regex *r, int len)
  *  not returns 1 if buff started with a '!'
  *     0 otherwise.
  */
-enum regex_type filter_parse_regex(char *buff, int len, char **search, int *not)
+enum regex_type filter_parse_regex(char *buff, int *len, char **search, int *not)
 {
 	int type = MATCH_FULL;
 	int i;
@@ -329,13 +329,13 @@ enum regex_type filter_parse_regex(char *buff, int len, char **search, int *not)
 	if (buff[0] == '!') {
 		*not = 1;
 		buff++;
-		len--;
+		(*len)--;
 	} else
 		*not = 0;
 
 	*search = buff;
 
-	for (i = 0; i < len; i++) {
+	for (i = 0; i < *len; i++) {
 		if (buff[i] == '*') {
 			if (!i) {
 				*search = buff + 1;
@@ -350,6 +350,7 @@ enum regex_type filter_parse_regex(char *buff, int len, char **search, int *not)
 			}
 		}
 	}
+	*len = strlen(*search);
 
 	return type;
 }
@@ -362,8 +363,7 @@ static void filter_build_regex(struct filter_pred *pred)
 	int not = 0;
 
 	if (pred->op == OP_GLOB) {
-		type = filter_parse_regex(r->pattern, r->len, &search, &not);
-		r->len = strlen(search);
+		type = filter_parse_regex(r->pattern, &r->len, &search, &not);
 		memmove(r->pattern, search, r->len+1);
 	}
 
-- 
2.1.4

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