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>

1 files changed, 41 insertions, 3 deletions

diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index 7ac691085276..01c76eb3e168 100644
--- 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;