From: H Hartley Sweeten <hsweeten@visionengravers.com>
Date: Wed, 9 Jan 2013 20:30:49 +0000 (-0700)
Subject: staging: comedi: comedi_buf: clarify comedi_buf_read_alloc()
X-Git-Url: http://drtracing.org/?a=commitdiff_plain;h=034cbd17922a8b6c64b227360314167c15c1f031;p=deliverable%2Flinux.git

staging: comedi: comedi_buf: clarify comedi_buf_read_alloc()

Clarify the check to make sure the number of bytes to allocate is
available.

Reword the comment about the need for the smp_rmb().

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/drivers/staging/comedi/comedi_buf.c b/drivers/staging/comedi/comedi_buf.c
index 06dd544ec2c5..971f7394a1f0 100644
--- a/drivers/staging/comedi/comedi_buf.c
+++ b/drivers/staging/comedi/comedi_buf.c
@@ -291,14 +291,20 @@ EXPORT_SYMBOL(comedi_buf_read_n_available);
 /* allocates a chunk for the reader from filled (and munged) buffer space */
 unsigned comedi_buf_read_alloc(struct comedi_async *async, unsigned nbytes)
 {
-	if ((int)(async->buf_read_alloc_count + nbytes - async->munge_count) >
-	    0) {
-		nbytes = async->munge_count - async->buf_read_alloc_count;
-	}
+	unsigned int available;
+
+	available = async->munge_count - async->buf_read_alloc_count;
+	if (nbytes > available)
+		nbytes = available;
+
 	async->buf_read_alloc_count += nbytes;
-	/* barrier insures read of munge_count occurs before we actually read
-	   data out of buffer */
+
+	/*
+	 * ensure the async buffer 'counts' are read before we
+	 * attempt to read data from the read-alloc'ed buffer space
+	 */
 	smp_rmb();
+
 	return nbytes;
 }
 EXPORT_SYMBOL(comedi_buf_read_alloc);