Re: [PATCH bpf-next] libbpf: remove zc variable as it is not used

["Jonathan Lemon" <jonathan.lemon@xxxxxxxxx>]

On 16 Aug 2019, at 8:37, Yonghong Song wrote:

> On 8/16/19 3:26 AM, Magnus Karlsson wrote:
> > The zc is not used in the xsk part of libbpf, so let us remove it. 
> > Not
> > good to have dead code lying around.
> >
> > Signed-off-by: Magnus Karlsson <magnus.karlsson@xxxxxxxxx>
> > Reported-by: Yonghong Song <yhs@xxxxxx> > ---
> >   tools/lib/bpf/xsk.c | 3 ---
> >   1 file changed, 3 deletions(-)
> >
> > diff --git a/tools/lib/bpf/xsk.c b/tools/lib/bpf/xsk.c
> > index 680e630..9687da9 100644
> > --- a/tools/lib/bpf/xsk.c
> > +++ b/tools/lib/bpf/xsk.c
> > @@ -65,7 +65,6 @@ struct xsk_socket {
> >   	int xsks_map_fd;
> >   	__u32 queue_id;
> >   	char ifname[IFNAMSIZ];
> > -	bool zc;
> >   };
> >
> >   struct xsk_nl_info {
> > @@ -608,8 +607,6 @@ int xsk_socket__create(struct xsk_socket 
> > **xsk_ptr, const char *ifname,
> >   		goto out_mmap_tx;
> >   	}
> >
> > -	xsk->zc = opts.flags & XDP_OPTIONS_ZEROCOPY;
>
> Since opts.flags usage is removed. Do you think it makes sense to
> remove
>          optlen = sizeof(opts);
>          err = getsockopt(xsk->fd, SOL_XDP, XDP_OPTIONS, &opts, 
> &optlen);
>          if (err) {
>                  err = -errno;
>                  goto out_mmap_tx;
>          }
> as well since nobody then uses opts?

IIRC, this was added specifically in 
2761ed4b6e192820760d5ba913834b2ba05fd08c
so that userland code could know whether the socket was operating in 
zero-copy
mode or not.
--
Jonathan