Willem de Bruijn <willemdebruijn.kernel@xxxxxxxxx> wrote: > That getfrag is needed. For non-splice cases, to fill the linear part > of an skb. As your example shows, it is skipped if all data is covered > by pagedlen? Yes, because copy goes negative. To quote from the previously quoted log: ==>splice_to_socket() 6630 udp_sendmsg(8,8) __ip_append_data(copy=-1,len=8, mtu=8192 skblen=8189 maxfl=8188) pagedlen 9 = 9 - 0 copy -1 = 9 - 0 - 1 - 9 copy is -(the number of excess bytes). length 8 -= -1 + 0 which then gets deducted from the length - but why? I wonder if copy should be cleared if we don't call getfrag(). It looks like it's meant to deduct the amount copied by getfrag(), but that doesn't happen if copy < 0. Also, note that MSG_ZEROCOPY might see the same maths issue here. David
