tracing/filters: support for filters of dynamic sized arrays

Currently the filtering infrastructure supports well the
numeric types and fixed sized array types.

But the recently added __string() field uses a specific
indirect offset mechanism which requires a specific
predicate. Until now it wasn't supported.

This patch adds this support and implies very few changes,
only a new predicate is needed, the management of this specific
field can be done through the usual string helpers in the
filtering infrastructure.

[ Impact: support all kinds of strings in the tracing filters ]

Cc: Tom Zanussi <tzanussi@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Zhaolei <zhaolei@cn.fujitsu.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>

diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index 7ac6910..01c76eb 100644 (file)
--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -151,6 +151,7 @@ static int filter_pred_or(struct filter_pred *pred __attribute((unused)),
        return val1 || val2;
 }
 
+/* Filter predicate for fixed sized arrays of characters */
 static int filter_pred_string(struct filter_pred *pred, void *event,
                              int val1, int val2)
 {
@@ -164,6 +165,30 @@ static int filter_pred_string(struct filter_pred *pred, void *event,
        return match;
 }
 
+/*
+ * Filter predicate for dynamic sized arrays of characters.
+ * These are implemented through a list of strings at the end
+ * of the entry.
+ * Also each of these strings have a field in the entry which
+ * contains its offset from the beginning of the entry.
+ * We have then first to get this field, dereference it
+ * and add it to the address of the entry, and at last we have
+ * the address of the string.
+ */
+static int filter_pred_strloc(struct filter_pred *pred, void *event,
+                             int val1, int val2)
+{
+       int str_loc = *(int *)(event + pred->offset);
+       char *addr = (char *)(event + str_loc);
+       int cmp, match;
+
+       cmp = strncmp(addr, pred->str_val, pred->str_len);
+
+       match = (!cmp) ^ pred->not;
+
+       return match;
+}
+
 static int filter_pred_none(struct filter_pred *pred, void *event,
                            int val1, int val2)
 {
@@ -446,10 +471,18 @@ static int filter_add_pred_fn(struct filter_parse_state *ps,
        return 0;
 }
 
+enum {
+       FILTER_STATIC_STRING = 1,
+       FILTER_DYN_STRING
+};
+
 static int is_string_field(const char *type)
 {
        if (strchr(type, '[') && strstr(type, "char"))
-               return 1;
+               return FILTER_STATIC_STRING;
+
+       if (!strcmp(type, "__str_loc"))
+               return FILTER_DYN_STRING;
 
        return 0;
 }
@@ -512,6 +545,7 @@ static int filter_add_pred(struct filter_parse_state *ps,
        struct ftrace_event_field *field;
        filter_pred_fn_t fn;
        unsigned long long val;
+       int string_type;
 
        pred->fn = filter_pred_none;
 
@@ -536,8 +570,12 @@ static int filter_add_pred(struct filter_parse_state *ps,
                return -EINVAL;
        }
 
-       if (is_string_field(field->type)) {
-               fn = filter_pred_string;
+       string_type = is_string_field(field->type);
+       if (string_type) {
+               if (string_type == FILTER_STATIC_STRING)
+                       fn = filter_pred_string;
+               else
+                       fn = filter_pred_strloc;
                pred->str_len = field->size;
                if (pred->op == OP_NE)
                        pred->not = 1;