ftrace: Allow to remove a single function from function graph filter

I don't see why we can only clear all functions from the filter.

After patching:

  # echo sys_open > set_graph_function
  # echo sys_close >> set_graph_function
  # cat set_graph_function
  sys_open
  sys_close
  # echo '!sys_close' >> set_graph_function
  # cat set_graph_function
  sys_open
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
LKML-Reference: <4B726388.2000408@cn.fujitsu.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

kernel/trace/ftrace.c

@@ -2426,6 +2426,7 @@ static const struct file_operations ftrace_notrace_fops = {
 static DEFINE_MUTEX(graph_lock);
 
 int ftrace_graph_count;
+int ftrace_graph_filter_enabled;
 unsigned long ftrace_graph_funcs[FTRACE_GRAPH_MAX_FUNCS] __read_mostly;
 
 static void *
@@ -2448,7 +2449,7 @@ static void *g_start(struct seq_file *m, loff_t *pos)
 	mutex_lock(&graph_lock);
 
 	/* Nothing, tell g_show to print all functions are enabled */
-	if (!ftrace_graph_count && !*pos)
+	if (!ftrace_graph_filter_enabled && !*pos)
 		return (void *)1;
 
 	return __g_next(m, pos);
@@ -2494,6 +2495,7 @@ ftrace_graph_open(struct inode *inode, struct file *file)
 	mutex_lock(&graph_lock);
 	if ((file->f_mode & FMODE_WRITE) &&
 	    (file->f_flags & O_TRUNC)) {
+		ftrace_graph_filter_enabled = 0;
 		ftrace_graph_count = 0;
 		memset(ftrace_graph_funcs, 0, sizeof(ftrace_graph_funcs));
 	}
@@ -2519,7 +2521,7 @@ ftrace_set_func(unsigned long *array, int *idx, char *buffer)
 	struct dyn_ftrace *rec;
 	struct ftrace_page *pg;
 	int search_len;
-	int found = 0;
+	int fail = 1;
 	int type, not;
 	char *search;
 	bool exists;
@@ -2530,37 +2532,51 @@ ftrace_set_func(unsigned long *array, int *idx, char *buffer)
 
 	/* decode regex */
 	type = filter_parse_regex(buffer, strlen(buffer), &search, &not);
-	if (not)
-		return -EINVAL;
+	if (!not && *idx >= FTRACE_GRAPH_MAX_FUNCS)
+		return -EBUSY;
 
 	search_len = strlen(search);
 
 	mutex_lock(&ftrace_lock);
 	do_for_each_ftrace_rec(pg, rec) {
 
-		if (*idx >= FTRACE_GRAPH_MAX_FUNCS)
-			break;
-
 		if (rec->flags & (FTRACE_FL_FAILED | FTRACE_FL_FREE))
 			continue;
 
 		if (ftrace_match_record(rec, search, search_len, type)) {
-			/* ensure it is not already in the array */
+			/* if it is in the array */
 			exists = false;
-			for (i = 0; i < *idx; i++)
+			for (i = 0; i < *idx; i++) {
 				if (array[i] == rec->ip) {
 					exists = true;
 					break;
 				}
-			if (!exists)
-				array[(*idx)++] = rec->ip;
-			found = 1;
+			}
+
+			if (!not) {
+				fail = 0;
+				if (!exists) {
+					array[(*idx)++] = rec->ip;
+					if (*idx >= FTRACE_GRAPH_MAX_FUNCS)
+						goto out;
+				}
+			} else {
+				if (exists) {
+					array[i] = array[--(*idx)];
+					array[*idx] = 0;
+					fail = 0;
+				}
+			}
 		}
 	} while_for_each_ftrace_rec();
-
+out:
 	mutex_unlock(&ftrace_lock);
 
-	return found ? 0 : -EINVAL;
+	if (fail)
+		return -EINVAL;
+
+	ftrace_graph_filter_enabled = 1;
+	return 0;
 }
 
 static ssize_t
@@ -2570,16 +2586,11 @@ ftrace_graph_write(struct file *file, const char __user *ubuf,
 	struct trace_parser parser;
 	ssize_t read, ret;
 
-	if (!cnt || cnt < 0)
+	if (!cnt)
 		return 0;
 
 	mutex_lock(&graph_lock);
 
-	if (ftrace_graph_count >= FTRACE_GRAPH_MAX_FUNCS) {
-		ret = -EBUSY;
-		goto out_unlock;
-	}
-
 	if (trace_parser_get_init(&parser, FTRACE_BUFF_MAX)) {
 		ret = -ENOMEM;
 		goto out_unlock;

kernel/trace/trace.h

@@ -497,6 +497,7 @@ trace_print_graph_duration(unsigned long long duration, struct trace_seq *s);
 #ifdef CONFIG_DYNAMIC_FTRACE
 /* TODO: make this variable */
 #define FTRACE_GRAPH_MAX_FUNCS		32
+extern int ftrace_graph_filter_enabled;
 extern int ftrace_graph_count;
 extern unsigned long ftrace_graph_funcs[FTRACE_GRAPH_MAX_FUNCS];
 
@@ -504,7 +505,7 @@ static inline int ftrace_graph_addr(unsigned long addr)
 {
 	int i;
 
-	if (!ftrace_graph_count)
+	if (!ftrace_graph_filter_enabled)
 		return 1;
 
 	for (i = 0; i < ftrace_graph_count; i++) {