[PATCH 09/11] staging: comedi: comedi_buf: clarify comedi_buf_read_alloc()

[Ian Abbott]

On 02/01/13 13:51, Ian Abbott wrote:
> On 2012-12-21 16:42, H Hartley Sweeten wrote:
>> Clarify the check to make sure the number of bytes to allocate is
>> available.
>>
>> Signed-off-by: H Hartley Sweeten <hsweeten at visionengravers.com>
>> Cc: Ian Abbott <abbobbi at mev.co.uk>
>> Cc: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
>> ---
>>    drivers/staging/comedi/comedi_buf.c | 8 ++++----
>>    1 file changed, 4 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/staging/comedi/comedi_buf.c b/drivers/staging/comedi/comedi_buf.c
>> index 246f577..1ec5aaa 100644
>> --- a/drivers/staging/comedi/comedi_buf.c
>> +++ b/drivers/staging/comedi/comedi_buf.c
>> @@ -298,10 +298,10 @@ 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;
>> -	}
>> +	int available = async->munge_count - async->buf_read_alloc_count;
>
> Minor nit-pick: that should be an unsigned int.
>
>> +
>> +	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 */

Thinking about this a bit more, I think it's worth skipping any changes 
to the buffer space calculations until unsigned integer overflows have 
been taken into consideration.

-- 
-=( Ian Abbott @ MEV Ltd.    E-mail: <abbotti at mev.co.uk>        )=-
-=( Tel: +44 (0)161 477 1898   FAX: +44 (0)161 718 3587         )=-