On Fri, Jun 5, 2020 at 4:01 AM Toke Høiland-Jørgensen <toke@xxxxxxxxxx> wrote: > > Jesper Dangaard Brouer <brouer@xxxxxxxxxx> writes: > > > On Thu, 4 Jun 2020 10:33:41 -0700 > > Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx> wrote: > > > >> On Thu, Jun 04, 2020 at 10:40:06AM -0600, David Ahern wrote: > >> > On 6/4/20 9:48 AM, Jesper Dangaard Brouer wrote: > >> > > I will NOT send a patch that expose this in uapi/bpf.h. As I explained > >> > > before, this caused the issues for my userspace application, that > >> > > automatically picked-up struct bpf_devmap_val, and started to fail > >> > > (with no code changes), because it needed minus-1 as input. I fear > >> > > that this will cause more work for me later, when I have to helpout and > >> > > support end-users on e.g. xdp-newbies list, as it will not be obvious > >> > > to end-users why their programs map-insert start to fail. I have given > >> > > up, so I will not NACK anyone sending such a patch. > >> > >> Jesper, > >> > >> you gave wrong direction to David during development of the patches and > >> now the devmap uapi is suffering the consequences. > >> > >> > > > >> > > Why is it we need to support file-descriptor zero as a valid > >> > > file-descriptor for a bpf-prog? > >> > > >> > That was a nice property of using the id instead of fd. And the init to > >> > -1 is not unique to this; adopters of the bpf_set_link_xdp_fd_opts for > >> > example have to do the same. > >> > >> I think it's better to adopt "fd==0 -> invalid" approach. > >> It won't be unique here. We're already using it in other places in bpf syscall. > >> I agree with Jesper that requiring -1 init of 2nd field is quite ugly > >> and inconvenient. > > > > Great. If we can remove this requirement of -1 init (and let zero mean > > feature isn't used), then I'm all for exposing expose in uapi/bpf.h. > > If we're going to officially deprecate fd 0 as a valid BPF fd, we should > at least make sure users don't end up with such an fd after opening a > BPF object. Not sure how the fd number assignment works, but could we > make sure that the kernel never returns fd 0 for a BPF program/map? > > Alternatively, we could add a check in libbpf and either reject the > call, or just call dup() before passing the fd to the kernel. Tweaking libbpf to do dup() was on our todo list for some time. I think it would be good to do it both in the kernel and in the libbpf.
