Improve devd startup time, by tweaking some string handling routines that are

heavily used when parsing config files.  Mostly these changes avoid making
temporary copies of the strings, and avoid doing byte at a time append
operations, on the most-used code path.

On a 1.2 GHz ARM processor this reduces the time to parse the config files
from 13 to 6 seconds.

Reviewed by:	imp
Approved by:	cognet (mentor)

2 files changed, 32 insertions, 25 deletions

diff --git a/sbin/devd/devd.cc b/sbin/devd/devd.cc
index c91430f..46f3623 100644
--- a/sbin/devd/devd.cc
+++ b/sbin/devd/devd.cc
@@ -137,7 +137,7 @@ config cfg;
 
 event_proc::event_proc() : _prio(-1)
 {
-	// nothing
+	_epsvec.reserve(4);
 }
 
 event_proc::~event_proc()
@@ -241,25 +241,18 @@ my_system(const char *command)
 bool
 action::do_action(config &c)
 {
-	string s = c.expand_string(_cmd);
+	string s = c.expand_string(_cmd.c_str());
 	if (Dflag)
 		fprintf(stderr, "Executing '%s'\n", s.c_str());
 	my_system(s.c_str());
 	return (true);
 }
 
-match::match(config &c, const char *var, const char *re)
-	: _var(var), _re("^")
+match::match(config &c, const char *var, const char *re) :
+	_inv(re[0] == '!'),
+	_var(var),
+	_re(c.expand_string(_inv ? re + 1 : re, "^", "$"))
 {
-	if (!c.expand_string(string(re)).empty() &&
-	    c.expand_string(string(re)).at(0) == '!') {
-		_re.append(c.expand_string(string(re)).substr(1));
-		_inv = 1;
-	} else {
-		_re.append(c.expand_string(string(re)));
-		_inv = 0;
-	}
-	_re.append("$");
 	regcomp(&_regex, _re.c_str(), REG_EXTENDED | REG_NOSUB | REG_ICASE);
 }
 
@@ -624,24 +617,37 @@ config::expand_one(const char *&src, string &dst)
 	do {
 		buffer.append(src++, 1);
 	} while (is_id_char(*src));
-	buffer.append("", 1);
 	dst.append(get_variable(buffer.c_str()));
 }
 
 const string
-config::expand_string(const string &s)
+config::expand_string(const char *src, const char *prepend, const char *append)
 {
-	const char *src;
+	const char *var_at;
 	string dst;
 
-	src = s.c_str();
-	while (*src) {
-		if (*src == '$')
-			expand_one(src, dst);
-		else
-			dst.append(src++, 1);
+	/*
+	 * 128 bytes is enough for 2427 of 2438 expansions that happen
+	 * while parsing config files, as tested on 2013-01-30.
+	 */
+	dst.reserve(128);
+
+	if (prepend != NULL)
+		dst = prepend;
+
+	for (;;) {
+		var_at = strchr(src, '$');
+		if (var_at == NULL) {
+			dst.append(src);
+			break;
+		}
+		dst.append(src, var_at - src);
+		src = var_at;
+		expand_one(src, dst);
 	}
-	dst.append("", 1);
+
+	if (append != NULL)
+		dst.append(append);
 
 	return (dst);
 }
diff --git a/sbin/devd/devd.hh b/sbin/devd/devd.hh
index 3613216..a48d07b 100644
--- a/sbin/devd/devd.hh
+++ b/sbin/devd/devd.hh
@@ -90,9 +90,9 @@ public:
 	virtual bool do_match(config &);
 	virtual bool do_action(config &) { return true; }
 private:
+	bool _inv;
 	std::string _var;
 	std::string _re;
-	bool _inv;
 	regex_t _regex;
 };
 
@@ -162,7 +162,8 @@ public:
 	void pop_var_table();
 	void set_variable(const char *var, const char *val);
 	const std::string &get_variable(const std::string &var);
-	const std::string expand_string(const std::string &var);
+	const std::string expand_string(const char * var, 
+	    const char * prepend = NULL, const char * append = NULL);
 	char *set_vars(char *);
 	void find_and_execute(char);
 protected: