Function kallsyms_on_each_symbol() traverses all symbols and submits each
symbol to the hook 'fn' for judgment and processing. For some cases, the
hook actually only handles the matched symbol, such as livepatch.

So that, we can first compress the name being looked up and then use
it for comparison when traversing 'kallsyms_names', this greatly reduces
the time consumed by traversing.

The pseudo code of the test case is as follows:
static int tst_find(void *data, const char *name,
		    struct module *mod, unsigned long addr)
{
	if (strcmp(name, "vmap") == 0)
		*(unsigned long *)data = addr;
        return 0;
}

static int tst_match(void *data, unsigned long addr)
{
        *(unsigned long *)data = addr;
        return 0;
}

start = sched_clock();
kallsyms_on_each_match_symbol(tst_match, "vmap", &addr);
end = sched_clock();

start = sched_clock();
kallsyms_on_each_symbol(tst_find, &addr);
end = sched_clock();

The test results are as follows (twice):
kallsyms_on_each_match_symbol:   557400,   583900
kallsyms_on_each_symbol      : 16659500, 16113950

kallsyms_on_each_match_symbol() consumes only 3.48% of
kallsyms_on_each_symbol()'s time.

--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c

@@ -305,6 +305,31 @@ int kallsyms_on_each_symbol(int (*fn)(void *, const char *, struct module *,
 	return 0;
 }
 
+int kallsyms_on_each_match_symbol(int (*fn)(void *, unsigned long),
+				  const char *name, void *data)
+{
+	unsigned int i, off;
+	int len, ret;
+	char namebuf[KSYM_NAME_LEN];
+
+	len = kallsyms_name_to_tokens(name, namebuf);
+	for (i = 0, off = 0; len && i < kallsyms_num_syms; i++) {
+		if ((i & 0xfff) == 0)
+			cond_resched();
+
+		if ((kallsyms_names[off] == len + 1) &&
+		    !memcmp(&kallsyms_names[off + 2], namebuf, len)) {
+			ret = fn(data, kallsyms_sym_address(i));
+			if (ret != 0)
+				return ret;
+			cond_resched();
+		}
+		off += kallsyms_names[off] + 1;