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staging: comedi: comedi_buf: clarify comedi_buf_read_free() 

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

Clarify the check to make sure the number of bytes to free is not
more than the number of bytes allocated.

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>
This commit is contained in:
H Hartley Sweeten 2013-01-09 13:31:16 -07:00 committed by Greg Kroah-Hartman
parent 034cbd1792
commit 3abfa1066b
1 changed files with 10 additions and 5 deletions
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15
drivers/staging/comedi/comedi_buf.c
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@ -312,14 +312,19 @@ EXPORT_SYMBOL(comedi_buf_read_alloc);
/* transfers control of a chunk from reader to free buffer space */
unsigned comedi_buf_read_free(struct comedi_async *async, unsigned int nbytes)
{
/* barrier insures data has been read out of
* buffer before read count is incremented */
unsigned int allocated;
/*
* ensure data has been read out of buffer before
* the async read count is incremented
*/
smp_mb();
if ((int)(async->buf_read_count + nbytes -
async->buf_read_alloc_count) > 0) {
allocated = comedi_buf_read_n_allocated(async);
if (nbytes > allocated) {
dev_info(async->subdevice->device->class_dev,
"attempted to read-free more bytes than have been read-allocated.\n");
nbytes = async->buf_read_alloc_count - async->buf_read_count;
nbytes = allocated;
}
async->buf_read_count += nbytes;
async->buf_read_ptr += nbytes;