[RFC PATCH 1/5] tracing: add trace_seq_vprint interface

[Steven Rostedt <rostedt@goodmis.org>]

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From: Steven Rostedt <srostedt@redhat.com>

The code to update the print formats for events requires a vprintf
format in the trace_seq. This patch adds that interface.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 include/linux/trace_seq.h   |    2 ++
 kernel/trace/trace_output.c |   32 ++++++++++++++++++++++++++++++++
 2 files changed, 34 insertions(+), 0 deletions(-)

diff --git a/include/linux/trace_seq.h b/include/linux/trace_seq.h
index ba9627f..c68bccb 100644
--- a/include/linux/trace_seq.h
+++ b/include/linux/trace_seq.h
@@ -27,6 +27,8 @@ trace_seq_init(struct trace_seq *s)
 #ifdef CONFIG_TRACING
 extern int trace_seq_printf(struct trace_seq *s, const char *fmt, ...)
 	__attribute__ ((format (printf, 2, 3)));
+extern int trace_seq_vprintf(struct trace_seq *s, const char *fmt, va_list args)
+	__attribute__ ((format (printf, 2, 0)));
 extern int
 trace_seq_bprintf(struct trace_seq *s, const char *fmt, const u32 *binary);
 extern void trace_print_seq(struct seq_file *m, struct trace_seq *s);
diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
index 425725c..c05aff4 100644
--- a/kernel/trace/trace_output.c
+++ b/kernel/trace/trace_output.c
@@ -100,6 +100,38 @@ trace_seq_printf(struct trace_seq *s, const char *fmt, ...)
 }
 EXPORT_SYMBOL_GPL(trace_seq_printf);
 
+/**
+ * trace_seq_vprintf - sequence printing of trace information
+ * @s: trace sequence descriptor
+ * @fmt: printf format string
+ *
+ * The tracer may use either sequence operations or its own
+ * copy to user routines. To simplify formating of a trace
+ * trace_seq_printf is used to store strings into a special
+ * buffer (@s). Then the output may be either used by
+ * the sequencer or pulled into another buffer.
+ */
+int
+trace_seq_vprintf(struct trace_seq *s, const char *fmt, va_list args)
+{
+	int len = (PAGE_SIZE - 1) - s->len;
+	int ret;
+
+	if (!len)
+		return 0;
+
+	ret = vsnprintf(s->buffer + s->len, len, fmt, args);
+
+	/* If we can't write it all, don't bother writing anything */
+	if (ret >= len)
+		return 0;
+
+	s->len += ret;
+
+	return len;
+}
+EXPORT_SYMBOL_GPL(trace_seq_vprintf);
+
 int trace_seq_bprintf(struct trace_seq *s, const char *fmt, const u32 *binary)
 {
 	int len = (PAGE_SIZE - 1) - s->len;
-- 
1.6.3.1

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