From 034cbd17922a8b6c64b227360314167c15c1f031 Mon Sep 17 00:00:00 2001 From: H Hartley Sweeten Date: Wed, 9 Jan 2013 13:30:49 -0700 Subject: [PATCH] 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 Signed-off-by: Ian Abbott Signed-off-by: Greg Kroah-Hartman --- drivers/staging/comedi/comedi_buf.c | 18 ++++++++++++------ 1 file changed, 12 insertions(+), 6 deletions(-) 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);