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Subject[PATCH 1/2] tracing/filters: support for filters of dynamic sized arrays
Date
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>
---
kernel/trace/trace_events_filter.c | 44 +++++++++++++++++++++++++++++++++--
1 files changed, 41 insertions(+), 3 deletions(-)
diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index f494866..4f0a128 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)
{
@@ -436,10 +461,18 @@ 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;
}
@@ -502,6 +535,7 @@ 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;

@@ -526,8 +560,12 @@ 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;
--
1.6.2.3


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