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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>
This commit is contained in:
H Hartley Sweeten 2013-01-09 13:30:49 -07:00 committed by Greg Kroah-Hartman
parent 43f9137df4
commit 034cbd1792
1 changed files with 12 additions and 6 deletions
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18
drivers/staging/comedi/comedi_buf.c
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@ -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);