[PATCH] fs: make simple_read_from_buffer conventional

[Steven Rostedt]

Impact: have simple_read_from_buffer conform to standards

It was brought to my attention by Andrew Morton, Theodore Tso,
and H. Peter Anvin that a read from userspace should only return
-EFAULT if nothing was actually read.

Looking at the simple_read_from_buffer I noticed that this function
does not conform to that rule. This patch fixes that function.

Signed-off-by: Steven Rostedt <srostedt@xxxxxxxxxx>

diff --git a/fs/libfs.c b/fs/libfs.c
index 49b4409..6a72298 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -525,14 +525,20 @@ ssize_t simple_read_from_buffer(void __user *to, size_t count, loff_t *ppos,
 				const void *from, size_t available)
 {
 	loff_t pos = *ppos;
+	size_t ret;
+
 	if (pos < 0)
 		return -EINVAL;
 	if (pos >= available)
 		return 0;
 	if (count > available - pos)
 		count = available - pos;
-	if (copy_to_user(to, from + pos, count))
-		return -EFAULT;
+	ret = copy_to_user(to, from + pos, count);
+	if (ret) {
+		if (ret == count)
+			return -EFAULT;
+		count -= ret;
+	}
 	*ppos = pos + count;
 	return count;
 }

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