Re: [v2,1/2] tools: bpftool: add net attach command to attach XDP on interface

["Daniel T. Lee" <danieltimlee@gmail.com>]

On Fri, Aug 2, 2019 at 3:23 PM Y Song <ys114321@gmail.com> wrote:
>
> On Thu, Aug 1, 2019 at 2:04 AM Daniel T. Lee <danieltimlee@gmail.com> wrote:
> >
> > By this commit, using `bpftool net attach`, user can attach XDP prog on
> > interface. New type of enum 'net_attach_type' has been made, as stated at
> > cover-letter, the meaning of 'attach' is, prog will be attached on interface.
> >
> > BPF prog will be attached through libbpf 'bpf_set_link_xdp_fd'.
> >
> > Signed-off-by: Daniel T. Lee <danieltimlee@gmail.com>
> > ---
> > Changes in v2:
> >   - command 'load' changed to 'attach' for the consistency
> >   - 'NET_ATTACH_TYPE_XDP_DRIVE' changed to 'NET_ATTACH_TYPE_XDP_DRIVER'
> >
> >  tools/bpf/bpftool/net.c | 107 +++++++++++++++++++++++++++++++++++++++-
> >  1 file changed, 106 insertions(+), 1 deletion(-)
> >
> > diff --git a/tools/bpf/bpftool/net.c b/tools/bpf/bpftool/net.c
> > index 67e99c56bc88..f3b57660b303 100644
> > --- a/tools/bpf/bpftool/net.c
> > +++ b/tools/bpf/bpftool/net.c
> > @@ -55,6 +55,35 @@ struct bpf_attach_info {
> >         __u32 flow_dissector_id;
> >  };
> >
> > +enum net_attach_type {
> > +       NET_ATTACH_TYPE_XDP,
> > +       NET_ATTACH_TYPE_XDP_GENERIC,
> > +       NET_ATTACH_TYPE_XDP_DRIVER,
> > +       NET_ATTACH_TYPE_XDP_OFFLOAD,
> > +       __MAX_NET_ATTACH_TYPE
> > +};
> > +
> > +static const char * const attach_type_strings[] = {
> > +       [NET_ATTACH_TYPE_XDP] = "xdp",
> > +       [NET_ATTACH_TYPE_XDP_GENERIC] = "xdpgeneric",
> > +       [NET_ATTACH_TYPE_XDP_DRIVER] = "xdpdrv",
> > +       [NET_ATTACH_TYPE_XDP_OFFLOAD] = "xdpoffload",
> > +       [__MAX_NET_ATTACH_TYPE] = NULL,
> > +};
> > +
> > +static enum net_attach_type parse_attach_type(const char *str)
> > +{
> > +       enum net_attach_type type;
> > +
> > +       for (type = 0; type < __MAX_NET_ATTACH_TYPE; type++) {
> > +               if (attach_type_strings[type] &&
> > +                  is_prefix(str, attach_type_strings[type]))
> > +                       return type;
> > +       }
> > +
> > +       return __MAX_NET_ATTACH_TYPE;
> > +}
> > +
> >  static int dump_link_nlmsg(void *cookie, void *msg, struct nlattr **tb)
> >  {
> >         struct bpf_netdev_t *netinfo = cookie;
> > @@ -223,6 +252,77 @@ static int query_flow_dissector(struct bpf_attach_info *attach_info)
> >         return 0;
> >  }
> >
> > +static int parse_attach_args(int argc, char **argv, int *progfd,
> > +                            enum net_attach_type *attach_type, int *ifindex)
> > +{
> > +       if (!REQ_ARGS(3))
> > +               return -EINVAL;
> > +
> > +       *progfd = prog_parse_fd(&argc, &argv);
> > +       if (*progfd < 0)
> > +               return *progfd;
> > +
> > +       *attach_type = parse_attach_type(*argv);
> > +       if (*attach_type == __MAX_NET_ATTACH_TYPE) {
> > +               p_err("invalid net attach/detach type");
> > +               return -EINVAL;
> > +       }
> > +
> > +       NEXT_ARG();
> > +       if (!REQ_ARGS(1))
> > +               return -EINVAL;
> > +
> > +       *ifindex = if_nametoindex(*argv);
> > +       if (!*ifindex) {
> > +               p_err("Invalid ifname");
>
> Do you want to use the full function name "invalid if_nametoindex" here?
>

No. I was trying to fix the message as "Invalid devname", since the
word "devanme"
is mentioned in 'bpftool net help'.

> > +               return -EINVAL;
> > +       }
> > +
> > +       return 0;
> > +}
> > +
> > +static int do_attach_detach_xdp(int *progfd, enum net_attach_type *attach_type,
> > +                               int *ifindex)
>
> You can just use plain int as the argument type here.
>

I will change the parameter as pass by value.

> > +{
> > +       __u32 flags;
> > +       int err;
> > +
> > +       flags = XDP_FLAGS_UPDATE_IF_NOEXIST;
> > +       if (*attach_type == NET_ATTACH_TYPE_XDP_GENERIC)
> > +               flags |= XDP_FLAGS_SKB_MODE;
> > +       if (*attach_type == NET_ATTACH_TYPE_XDP_DRIVER)
> > +               flags |= XDP_FLAGS_DRV_MODE;
> > +       if (*attach_type == NET_ATTACH_TYPE_XDP_OFFLOAD)
> > +               flags |= XDP_FLAGS_HW_MODE;
> > +
> > +       err = bpf_set_link_xdp_fd(*ifindex, *progfd, flags);
> > +
> > +       return err;
>
> Just do "return bpf_set_link_xdp_fd(...)" and you do not need variable err.
>

Oh. I've misunderstood why variable err won't be needed.
I'll remove the variable err and update to it.

> > +}
> > +
> > +static int do_attach(int argc, char **argv)
> > +{
> > +       enum net_attach_type attach_type;
> > +       int err, progfd, ifindex;
> > +
> > +       err = parse_attach_args(argc, argv, &progfd, &attach_type, &ifindex);
> > +       if (err)
> > +               return err;
> > +
> > +       if (is_prefix("xdp", attach_type_strings[attach_type]))
> > +               err = do_attach_detach_xdp(&progfd, &attach_type, &ifindex);
> > +
> > +       if (err < 0) {
> > +               p_err("link set %s failed", attach_type_strings[attach_type]);
> > +               return -1;
> > +       }
>
> The above "if (err < 0)" can be true only under the above "if (is_prefix(..))"
> conditions. But compiler may optimize this. So I think current form is okay.
> But could you change the return value to "return err" instead of "return -1"?
>

Okay. I'll update the return value to "return err".

> > +
> > +       if (json_output)
> > +               jsonw_null(json_wtr);
> > +
> > +       return 0;
> > +}
> > +
> >  static int do_show(int argc, char **argv)
> >  {
> >         struct bpf_attach_info attach_info = {};
> > @@ -305,13 +405,17 @@ static int do_help(int argc, char **argv)
> >
> >         fprintf(stderr,
> >                 "Usage: %s %s { show | list } [dev <devname>]\n"
> > +               "       %s %s attach PROG LOAD_TYPE <devname>\n"
> >                 "       %s %s help\n"
> > +               "\n"
> > +               "       " HELP_SPEC_PROGRAM "\n"
> > +               "       LOAD_TYPE := { xdp | xdpgeneric | xdpdrv | xdpoffload }\n"
> >                 "Note: Only xdp and tc attachments are supported now.\n"
> >                 "      For progs attached to cgroups, use \"bpftool cgroup\"\n"
> >                 "      to dump program attachments. For program types\n"
> >                 "      sk_{filter,skb,msg,reuseport} and lwt/seg6, please\n"
> >                 "      consult iproute2.\n",
> > -               bin_name, argv[-2], bin_name, argv[-2]);
> > +               bin_name, argv[-2], bin_name, argv[-2], bin_name, argv[-2]);
> >
> >         return 0;
> >  }
> > @@ -319,6 +423,7 @@ static int do_help(int argc, char **argv)
> >  static const struct cmd cmds[] = {
> >         { "show",       do_show },
> >         { "list",       do_show },
> > +       { "attach",     do_attach },
> >         { "help",       do_help },
> >         { 0 }
> >  };
> > --
> > 2.20.1
> >

Thank you for the review :)