linux-kernel - [RFC PATCH 09/17] tracing: Add seq_buf_get_buf() and seq_buf

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Date:	Thu, 14 May 2015 11:34:56 +0000
From:	Wang Long <long.wanglong@...wei.com>
To:	<rostedt@...dmis.org>, <jkosina@...e.cz>,
	<gregkh@...uxfoundation.org>
CC:	<stable@...r.kernel.org>, <wanglong@...qinren.net>,
	<peifeiyue@...wei.com>, <linux-kernel@...r.kernel.org>,
	<morgan.wang@...wei.com>, <paulmck@...ux.vnet.ibm.com>,
	<pmladek@...e.cz>, <dzickus@...hat.com>, <x86@...nel.org>,
	<sasha.levin@...cle.com>
Subject: [RFC PATCH 09/17] tracing: Add seq_buf_get_buf() and seq_buf_commit() helper functions

From: "Steven Rostedt (Red Hat)" <rostedt@...dmis.org>

commit 01cb06a4c229908d239149017049fdd1fca1dd51 upstream.

Add two helper functions; seq_buf_get_buf() and seq_buf_commit() that
are used by seq_buf_path(). This makes the code similar to the
seq_file: seq_path() function, and will help to be able to consolidate
the functions between seq_file and trace_seq.

Link: http://lkml.kernel.org/r/20141104160222.644881406@goodmis.org
Link: http://lkml.kernel.org/r/20141114011412.977571447@goodmis.org

Tested-by: Jiri Kosina <jkosina@...e.cz>
Acked-by: Jiri Kosina <jkosina@...e.cz>
Reviewed-by: Petr Mladek <pmladek@...e.cz>
[wanglong: backport to 3.10 stable]
Signed-off-by: Wang Long <long.wanglong@...wei.com>
Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
---
 include/linux/seq_buf.h | 41 +++++++++++++++++++++++++++++++++++++++++
 kernel/trace/seq_buf.c  |  7 +++----
 2 files changed, 44 insertions(+), 4 deletions(-)

diff --git a/include/linux/seq_buf.h b/include/linux/seq_buf.h
index 0800a24..12c6428 100644
--- a/include/linux/seq_buf.h
+++ b/include/linux/seq_buf.h
@@ -70,6 +70,47 @@ static inline unsigned int seq_buf_used(struct seq_buf *s)
 	return min(s->len, s->size);
 }
 
+/**
+ * seq_buf_get_buf - get buffer to write arbitrary data to
+ * @s: the seq_buf handle
+ * @bufp: the beginning of the buffer is stored here
+ *
+ * Return the number of bytes available in the buffer, or zero if
+ * there's no space.
+ */
+static inline size_t seq_buf_get_buf(struct seq_buf *s, char **bufp)
+{
+	WARN_ON(s->len > s->size + 1);
+
+	if (s->len < s->size) {
+		*bufp = s->buffer + s->len;
+		return s->size - s->len;
+	}
+
+	*bufp = NULL;
+	return 0;
+}
+
+/**
+ * seq_buf_commit - commit data to the buffer
+ * @s: the seq_buf handle
+ * @num: the number of bytes to commit
+ *
+ * Commit @num bytes of data written to a buffer previously acquired
+ * by seq_buf_get.  To signal an error condition, or that the data
+ * didn't fit in the available space, pass a negative @num value.
+ */
+static inline void seq_buf_commit(struct seq_buf *s, int num)
+{
+	if (num < 0) {
+		seq_buf_set_overflow(s);
+	} else {
+		/* num must be negative on overflow */
+		BUG_ON(s->len + num > s->size);
+		s->len += num;
+	}
+}
+
 extern __printf(2, 3)
 int seq_buf_printf(struct seq_buf *s, const char *fmt, ...);
 extern __printf(2, 0)
diff --git a/kernel/trace/seq_buf.c b/kernel/trace/seq_buf.c
index c53f1d5..086f594 100644
--- a/kernel/trace/seq_buf.c
+++ b/kernel/trace/seq_buf.c
@@ -293,8 +293,8 @@ int seq_buf_putmem_hex(struct seq_buf *s, const void *mem,
  */
 int seq_buf_path(struct seq_buf *s, const struct path *path, const char *esc)
 {
-	char *buf = s->buffer + s->len;
-	size_t size = seq_buf_buffer_left(s);
+	char *buf;
+	size_t size = seq_buf_get_buf(s, &buf);
 	int res = -1;
 
 	WARN_ON(s->size == 0);
@@ -307,8 +307,7 @@ int seq_buf_path(struct seq_buf *s, const struct path *path, const char *esc)
 				res = end - buf;
 		}
 	}
-	if (res > 0)
-		s->len += res;
+	seq_buf_commit(s, res);
 
 	return res;
 }
-- 
1.8.3.4

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