[PATCH 2/4] tracing: convert event_trace to use copy_word_from_user

[Steven Rostedt <rostedt@goodmis.org>]

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From: Steven Rostedt <srostedt@redhat.com>

Impact: clean up

This patch converts the open coded retrieving of a word from user
space to use copy_word_from_user.

Also removed a cnt < 0 check that Andrew Morton pointed out saying
that it was irrelevant since cnt is unsigned.

Also changed file->pos += to (*ppos) += which is the proper way
to modify positions of the file.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
---
 kernel/trace/trace_events.c |   78 +++++++++++++++++++------------------------
 1 files changed, 34 insertions(+), 44 deletions(-)

diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 3bcb9df..91ed36c 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -80,62 +80,52 @@ static ssize_t
 ftrace_event_write(struct file *file, const char __user *ubuf,
 		   size_t cnt, loff_t *ppos)
 {
-	size_t read = 0;
-	int i, set = 1;
+	unsigned int copied;
+	size_t read;
 	ssize_t ret;
+	int set = 1;
 	char *buf;
-	char ch;
 
-	if (!cnt || cnt < 0)
+	if (!cnt)
 		return 0;
 
-	ret = get_user(ch, ubuf++);
-	if (ret)
-		return ret;
-	read++;
-	cnt--;
-
-	/* skip white space */
-	while (cnt && isspace(ch)) {
-		ret = get_user(ch, ubuf++);
-		if (ret)
-			return ret;
-		read++;
-		cnt--;
-	}
-
-	/* Only white space found? */
-	if (isspace(ch)) {
-		file->f_pos += read;
-		ret = read;
-		return ret;
-	}
-
 	buf = kmalloc(EVENT_BUF_SIZE+1, GFP_KERNEL);
 	if (!buf)
 		return -ENOMEM;
 
-	if (cnt > EVENT_BUF_SIZE)
-		cnt = EVENT_BUF_SIZE;
-
-	i = 0;
-	while (cnt && !isspace(ch)) {
-		if (!i && ch == '!')
-			set = 0;
-		else
-			buf[i++] = ch;
-
-		ret = get_user(ch, ubuf++);
-		if (ret)
-			goto out_free;
-		read++;
-		cnt--;
+	ret = copy_word_from_user(buf, ubuf, EVENT_BUF_SIZE,
+				  cnt, &copied, 1);
+
+	if (ret == -EAGAIN) {
+		/*
+		 * echo > set_event
+		 *  This will cause copy_word_from_user to return -EAGAIN
+		 *  but copied will be 0.
+		 */
+		if (!copied) {
+			ret = cnt;
+			(*ppos) += cnt;
+		}
+		/* TODO, handle split words */
+		goto out_free;
 	}
-	buf[i] = 0;
 
-	file->f_pos += read;
+	if (ret < 0)
+		goto out_free;
+
+	buf[copied] = 0;
+
+	if (buf[0] == '!')
+		set = 0;
+
+	(*ppos) += ret;
+	read = ret;
 
-	ret = ftrace_set_clr_event(buf, set);
+	/*
+	 * A little hack here. If set is true, we want to use buf.
+	 * Otherwise, we want to use buf+1 (to skip the '!').
+	 */
+	ret = ftrace_set_clr_event(buf + !set, set);
 	if (ret)
 		goto out_free;
 
-- 
1.5.6.5

--