Re: [PATCH bpf-next] bpftool: specify XDP Hints ifname when loading program

[Niklas Söderlund]

On 2023-05-12 15:36:47 +0200, Larysa Zaremba wrote:
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> 
> On Fri, May 12, 2023 at 11:23:00AM +0100, Quentin Monnet wrote:
> > 2023-05-11 17:13 UTC+0200 ~ Larysa Zaremba <larysa.zaremba@xxxxxxxxx>
> > > Add ability to specify a network interface used to resolve
> > > XDP Hints kfuncs when loading program through bpftool.
> > >
> > > Usage:
> > > bpftool prog load <bpf_obj_path> <pin_path> dev xdpmeta <ifname>
> >
> > Thanks for this patch!
> >
> > Regarding the command-line syntax, I'm not a big fan of the optional
> > sub-keyword for the device for XDP hints. I must admit I had not
> > anticipated other another use for the "dev" keyword. Instead, have you
> > considered one of the following:
> >
> > 1) Adding a different keyword ("xdpmeta_dev"?) and making it
> > incompatible with "dev"
> >
> > 2) Another alternative would be adding a sub-keyword for offload too:
> >
> >     bpftool p l [...] dev <[offload <ifname> | xdpmeta <ifname>]>
> >
> > If the ifname is provided with no sub-keyword, we would consider it for
> > offload for legacy support, possibly warn that the syntax is deprecated.
> >
> > What do you think?
> >
> 
> I think first option would look a little bit nicer, but I like the idea to
> deprecate "dev <ifname>". In my current version, forgetting to add "xdpmeta"
> resulted in not very descriptive errors, this may confuse new users. So what
> about:

I agree the first option looks a little bit nicer, but I think both 
options would work.

> 
> bpftool prog load [...] xdpmeta_dev/offload_dev <ifname>
> 
> "dev <ifname>" syntax would still work, but with a big warning, like this:
> 
>   'bpftool prog [...] dev <ifname>' syntax is deprecated. Going further, please
>   use 'offload_dev <ifname>' to offload program to device. For XDP hints
>   applications, use 'xdpmeta_dev <ifname>'.
> 
> > >
> > > Signed-off-by: Larysa Zaremba <larysa.zaremba@xxxxxxxxx>
> > > ---
> > >  tools/bpf/bpftool/prog.c | 28 +++++++++++++++++++++-------
> > >  1 file changed, 21 insertions(+), 7 deletions(-)
> > >
> > > diff --git a/tools/bpf/bpftool/prog.c b/tools/bpf/bpftool/prog.c
> > > index 91b6075b2db3..a9cb96d99277 100644
> > > --- a/tools/bpf/bpftool/prog.c
> > > +++ b/tools/bpf/bpftool/prog.c
> > > @@ -1517,12 +1517,13 @@ static int load_with_options(int argc, char **argv, bool first_prog_only)
> > >     struct bpf_program *prog = NULL, *pos;
> > >     unsigned int old_map_fds = 0;
> > >     const char *pinmaps = NULL;
> > > +   __u32 offload_ifindex = 0;
> > >     bool auto_attach = false;
> > > +   __u32 meta_ifindex = 0;
> > >     struct bpf_object *obj;
> > >     struct bpf_map *map;
> > >     const char *pinfile;
> > >     unsigned int i, j;
> > > -   __u32 ifindex = 0;
> > >     const char *file;
> > >     int idx, err;
> > >
> > > @@ -1614,17 +1615,25 @@ static int load_with_options(int argc, char **argv, bool first_prog_only)
> > >                     map_replace[old_map_fds].fd = fd;
> > >                     old_map_fds++;
> > >             } else if (is_prefix(*argv, "dev")) {
> > > +                   __u32 *cur_ifindex;
> > > +
> > >                     NEXT_ARG();
> > >
> > > -                   if (ifindex) {
> > > -                           p_err("offload device already specified");
> > > +                   if (offload_ifindex || meta_ifindex) {
> > > +                           p_err("device already specified");
> >
> > I'd add a note to tell somehow that offload and XDP hints are mutually
> > exclusive. I suspect not all users understand these well.
> 
> Ok, will do.
> 
> >
> > >                             goto err_free_reuse_maps;
> > >                     }
> > > +                   if (is_prefix(*argv, "xdpmeta")) {
> > > +                           cur_ifindex = &meta_ifindex;
> > > +                           NEXT_ARG();
> > > +                   } else {
> > > +                           cur_ifindex = &offload_ifindex;
> > > +                   }
> > >                     if (!REQ_ARGS(1))
> > >                             goto err_free_reuse_maps;
> > >
> > > -                   ifindex = if_nametoindex(*argv);
> > > -                   if (!ifindex) {
> > > +                   *cur_ifindex = if_nametoindex(*argv);
> > > +                   if (!(*cur_ifindex)) {
> > >                             p_err("unrecognized netdevice '%s': %s",
> > >                                   *argv, strerror(errno));
> > >                             goto err_free_reuse_maps;
> > > @@ -1671,7 +1680,12 @@ static int load_with_options(int argc, char **argv, bool first_prog_only)
> > >                             goto err_close_obj;
> > >             }
> > >
> > > -           bpf_program__set_ifindex(pos, ifindex);
> > > +           if (prog_type == BPF_PROG_TYPE_XDP && meta_ifindex) {
> > > +                   bpf_program__set_flags(pos, BPF_F_XDP_DEV_BOUND_ONLY);
> > > +                   bpf_program__set_ifindex(pos, meta_ifindex);
> > > +           } else {
> > > +                   bpf_program__set_ifindex(pos, offload_ifindex);
> > > +           }
> > >             if (bpf_program__type(pos) != prog_type)
> > >                     bpf_program__set_type(pos, prog_type);
> > >             bpf_program__set_expected_attach_type(pos, expected_attach_type);
> > > @@ -1709,7 +1723,7 @@ static int load_with_options(int argc, char **argv, bool first_prog_only)
> > >     idx = 0;
> > >     bpf_object__for_each_map(map, obj) {
> > >             if (bpf_map__type(map) != BPF_MAP_TYPE_PERF_EVENT_ARRAY)
> > > -                   bpf_map__set_ifindex(map, ifindex);
> > > +                   bpf_map__set_ifindex(map, offload_ifindex);
> > >
> > >             if (j < old_map_fds && idx == map_replace[j].idx) {
> > >                     err = bpf_map__reuse_fd(map, map_replace[j++].fd);
> >
> > Could you please also update the following items:
> >
> > - The usage message for "bpftool prog load" near the end of prog.c
> >
> > - The related doc in Documentation/bpftool-prog.rst (command summary
> > near the top, and detailed description later in the doc)
> >
> > - Bash completion (for keyword "dev", look for "_sysfs_get_netdevs" in
> > bash-completion/bpftool). I'm happy to help with this one if necessary.
> 
> Will do all the above in v2.
> 
> >
> > Thanks,
> > Quentin

-- 
Kind Regards,
Niklas Söderlund