[PATCH 4/7] tracing/filters: allow user to specify a filter val to be string

[Li Zefan <lizf@cn.fujitsu.com>]

Suppose we would like to trace all tasks named '123', but this
will fail:
 # echo 'parent_comm == 123' > events/sched/sched_process_fork/filter
 bash: echo: write error: Invalid argument

With this patch, we allow it by:
 # echo 'parent_comm == \123' > events/sched/sched_process_fork/filter
 # cat events/sched/sched_process_fork/filter
 parent_comm == 123

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
---
 kernel/trace/trace_events_filter.c |   11 ++++++++++-
 1 files changed, 10 insertions(+), 1 deletions(-)

diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index 49b3ef5..2bf4481 100644
--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -351,12 +351,19 @@ oom:
 	return -ENOMEM;
 }
 
+/*
+ * The filter format can be
+ *   - 0, which means remove all filter preds
+ *   - [||/&&] <field> ==/!= [\]<val>
+ *
+ * Note: '\' prevent a string type value beginning with a digit to
+ *       be treated as a number
+ */
 int filter_parse(char **pbuf, struct filter_pred *pred)
 {
 	char *tmp, *tok, *val_str = NULL;
 	int tok_n = 0;
 
-	/* field ==/!= number, or/and field ==/!= number, number */
 	while ((tok = strsep(pbuf, " \n"))) {
 		if (tok_n == 0) {
 			if (!strcmp(tok, "0")) {
@@ -421,6 +428,8 @@ int filter_parse(char **pbuf, struct filter_pred *pred)
 
 	pred->val = simple_strtoull(val_str, &tmp, 0);
 	if (tmp == val_str) {
+		if (*val_str == '\\')
+			val_str++;
 		pred->str_val = kstrdup(val_str, GFP_KERNEL);
 		if (!pred->str_val)
 			return -ENOMEM;
-- 
1.5.4.rc3