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
