On 11/10/2017 9:43 AM, Herbert Xu wrote:
> On Fri, Nov 10, 2017 at 06:37:22AM +0000, Horia Geantă wrote:
>> On 11/10/2017 12:21 AM, Herbert Xu wrote:
>>> On Thu, Nov 09, 2017 at 02:37:29PM +0000, Horia Geantă wrote:
>>>>
>>>>>> sg_init_table(sg, np + 1);
>>>> sg_mark_end() marks sg[np].
>>>>
>>>>>> - np--;
>>>>>> + if (rem)
>>>>>> + np--;
>>>>>> for (k = 0; k < np; k++)
>>>>>> sg_set_buf(&sg[k + 1], xbuf[k], PAGE_SIZE);
>>>> In case rem == 0, last k value is np-1, thus sg[np-1+1] will be filled
>>>> here with xbuf[np-1].
>>>
>>> No, if rem == 0, then the last k value is np-2.
>>>
>> Notice that np-- above the for loop is done conditionally, so in the for
>> loop k takes values in [0, np-1].
>> This means the for loop fills sg[1]...sg[np].
>
> I must be missing something. In the case rem == 0, let's say
> the original value of np is npo. Then at the start of the loop,
> np = npo - 1, and at the last iteration, k = npo - 2, so we do
IIUC at the start of the loop np = npo (and not npo - 1), since np is no
longer decremented in the rem == 0 case:
- np--;
+ if (rem)
+ np--;
>
> sg_set_buf(&sg[npo - 1], xbuf[npo - 2], PAGE_SIZE);
>
and accordingly last iteration is for k = npo - 1:
sg_set_buf(&sg[npo], xbuf[npo - 1], PAGE_SIZE);
> While the sg_init_table call sets the end-of-table at
>
> sg_init_table(sg, npo + 1);
>
while this marks sg[npo] as last SG table entry.
Thanks,
Horia
