tracing: create generic trace parser

Create a "trace_parser" that can parse the user space input for
separate words.

struct trace_parser is the descriptor.

Generic "trace_get_user" function that can be a helper to read multiple
words passed in by user space.

Signed-off-by: Jiri Olsa <jolsa@redhat.com>
LKML-Reference: <1252682969-3366-2-git-send-email-jolsa@redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

2 files changed, 141 insertions, 0 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 3b918283cf94..45c3f0352d78 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -339,6 +339,112 @@ static struct {
 
 int trace_clock_id;
 
+/*
+ * trace_parser_get_init - gets the buffer for trace parser
+ */
+int trace_parser_get_init(struct trace_parser *parser, int size)
+{
+        memset(parser, 0, sizeof(*parser));
+
+        parser->buffer = kmalloc(size, GFP_KERNEL);
+        if (!parser->buffer)
+                return 1;
+
+        parser->size = size;
+        return 0;
+}
+
+/*
+ * trace_parser_put - frees the buffer for trace parser
+ */
+void trace_parser_put(struct trace_parser *parser)
+{
+        kfree(parser->buffer);
+}
+
+/*
+ * trace_get_user - reads the user input string separated by  space
+ * (matched by isspace(ch))
+ *
+ * For each string found the 'struct trace_parser' is updated,
+ * and the function returns.
+ *
+ * Returns number of bytes read.
+ *
+ * See kernel/trace/trace.h for 'struct trace_parser' details.
+ */
+int trace_get_user(struct trace_parser *parser, const char __user *ubuf,
+        size_t cnt, loff_t *ppos)
+{
+        char ch;
+        size_t read = 0;
+        ssize_t ret;
+
+        if (!*ppos)
+                trace_parser_clear(parser);
+
+        ret = get_user(ch, ubuf++);
+        if (ret)
+                goto out;
+
+        read++;
+        cnt--;
+
+        /*
+         * The parser is not finished with the last write,
+         * continue reading the user input without skipping spaces.
+         */
+        if (!parser->cont) {
+                /* skip white space */
+                while (cnt && isspace(ch)) {
+                        ret = get_user(ch, ubuf++);
+                        if (ret)
+                                goto out;
+                        read++;
+                        cnt--;
+                }
+
+                /* only spaces were written */
+                if (isspace(ch)) {
+                        *ppos += read;
+                        ret = read;
+                        goto out;
+                }
+
+                parser->idx = 0;
+        }
+
+        /* read the non-space input */
+        while (cnt && !isspace(ch)) {
+                if (parser->idx < parser->size)
+                        parser->buffer[parser->idx++] = ch;
+                else {
+                        ret = -EINVAL;
+                        goto out;
+                }
+                ret = get_user(ch, ubuf++);
+                if (ret)
+                        goto out;
+                read++;
+                cnt--;
+        }
+
+        /* We either got finished input or we have to wait for another call. */
+        if (isspace(ch)) {
+                parser->buffer[parser->idx] = 0;
+                parser->cont = false;
+        } else {
+                parser->cont = true;
+                parser->buffer[parser->idx++] = ch;
+        }
+
+        *ppos += read;
+        ret = read;
+
+out:
+        return ret;
+}
+
 ssize_t trace_seq_to_user(struct trace_seq *s, char __user *ubuf, size_t cnt)
 {
         int len;
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index b69697b4b846..28247cecd955 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -616,6 +616,41 @@ static inline int ftrace_trace_task(struct task_struct *task)
 #endif
 
 /*
+ * struct trace_parser - servers for reading the user input separated by spaces
+ * @cont: set if the input is not complete - no final space char was found
+ * @buffer: holds the parsed user input
+ * @idx: user input lenght
+ * @size: buffer size
+ */
+struct trace_parser {
+        bool            cont;
+        char            *buffer;
+        unsigned        idx;
+        unsigned        size;
+};
+
+static inline bool trace_parser_loaded(struct trace_parser *parser)
+{
+        return (parser->idx != 0);
+}
+
+static inline bool trace_parser_cont(struct trace_parser *parser)
+{
+        return parser->cont;
+}
+
+static inline void trace_parser_clear(struct trace_parser *parser)
+{
+        parser->cont = false;
+        parser->idx = 0;
+}
+
+extern int trace_parser_get_init(struct trace_parser *parser, int size);
+extern void trace_parser_put(struct trace_parser *parser);
+extern int trace_get_user(struct trace_parser *parser, const char __user *ubuf,
+        size_t cnt, loff_t *ppos);
+
+/*
  * trace_iterator_flags is an enumeration that defines bit
  * positions into trace_flags that controls the output.
  *