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Date: Wed, 16 Sep 2020 13:45:33 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Toke Høiland-Jørgensen <toke@...hat.com>
Cc: Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Martin KaFai Lau <kafai@...com>,
Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
Andrii Nakryiko <andriin@...com>,
John Fastabend <john.fastabend@...il.com>,
Jiri Olsa <jolsa@...hat.com>,
Eelco Chaudron <echaudro@...hat.com>,
KP Singh <kpsingh@...omium.org>,
Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH bpf-next v5 6/8] libbpf: add support for freplace
attachment in bpf_link_create
On Wed, Sep 16, 2020 at 1:37 PM Andrii Nakryiko
<andrii.nakryiko@...il.com> wrote:
>
> On Tue, Sep 15, 2020 at 5:50 PM Toke Høiland-Jørgensen <toke@...hat.com> wrote:
> >
> > From: Toke Høiland-Jørgensen <toke@...hat.com>
> >
> > This adds support for supplying a target btf ID for the bpf_link_create()
> > operation, and adds a new bpf_program__attach_freplace() high-level API for
> > attaching freplace functions with a target.
> >
> > Signed-off-by: Toke Høiland-Jørgensen <toke@...hat.com>
> > ---
> > tools/lib/bpf/bpf.c | 1 +
> > tools/lib/bpf/bpf.h | 3 ++-
> > tools/lib/bpf/libbpf.c | 24 ++++++++++++++++++------
> > tools/lib/bpf/libbpf.h | 3 +++
> > tools/lib/bpf/libbpf.map | 1 +
> > 5 files changed, 25 insertions(+), 7 deletions(-)
> >
> > diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
> > index 82b983ff6569..e928456c0dd6 100644
> > --- a/tools/lib/bpf/bpf.c
> > +++ b/tools/lib/bpf/bpf.c
> > @@ -599,6 +599,7 @@ int bpf_link_create(int prog_fd, int target_fd,
> > attr.link_create.iter_info =
> > ptr_to_u64(OPTS_GET(opts, iter_info, (void *)0));
> > attr.link_create.iter_info_len = OPTS_GET(opts, iter_info_len, 0);
> > + attr.link_create.target_btf_id = OPTS_GET(opts, target_btf_id, 0);
> >
> > return sys_bpf(BPF_LINK_CREATE, &attr, sizeof(attr));
> > }
> > diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
> > index 015d13f25fcc..f8dbf666b62b 100644
> > --- a/tools/lib/bpf/bpf.h
> > +++ b/tools/lib/bpf/bpf.h
> > @@ -174,8 +174,9 @@ struct bpf_link_create_opts {
> > __u32 flags;
> > union bpf_iter_link_info *iter_info;
> > __u32 iter_info_len;
> > + __u32 target_btf_id;
> > };
> > -#define bpf_link_create_opts__last_field iter_info_len
> > +#define bpf_link_create_opts__last_field target_btf_id
> >
> > LIBBPF_API int bpf_link_create(int prog_fd, int target_fd,
> > enum bpf_attach_type attach_type,
> > diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> > index 550950eb1860..165131c73f40 100644
> > --- a/tools/lib/bpf/libbpf.c
> > +++ b/tools/lib/bpf/libbpf.c
> > @@ -9322,12 +9322,14 @@ static struct bpf_link *attach_iter(const struct bpf_sec_def *sec,
> >
> > static struct bpf_link *
> > bpf_program__attach_fd(struct bpf_program *prog, int target_fd,
> > - const char *target_name)
> > + int target_btf_id, const char *target_name)
> > {
> > enum bpf_attach_type attach_type;
> > char errmsg[STRERR_BUFSIZE];
> > struct bpf_link *link;
> > int prog_fd, link_fd;
> > + DECLARE_LIBBPF_OPTS(bpf_link_create_opts, opts,
> > + .target_btf_id = target_btf_id);
> >
> > prog_fd = bpf_program__fd(prog);
> > if (prog_fd < 0) {
> > @@ -9340,8 +9342,12 @@ bpf_program__attach_fd(struct bpf_program *prog, int target_fd,
> > return ERR_PTR(-ENOMEM);
> > link->detach = &bpf_link__detach_fd;
> >
> > - attach_type = bpf_program__get_expected_attach_type(prog);
> > - link_fd = bpf_link_create(prog_fd, target_fd, attach_type, NULL);
> > + if (bpf_program__get_type(prog) == BPF_PROG_TYPE_EXT)
> > + attach_type = BPF_TRACE_FREPLACE;
>
> doing this unconditionally will break an old-style freplace without
> target_fd/btf_id on older kernels. Safe and simple way would be to
> continue using raw_tracepoint_open when there is no target_fd/btf_id,
> and use LINK_CREATE for newer stuff. Alternatively, you'd need to do
> feature detection, but it's still would be nice to handle old-style
> attach through raw_tracepoint_open for bpf_program__attach_freplace.
>
> so I suggest leaving bpf_program__attach_fd() as is and to create a
> custom bpf_program__attach_freplace() implementation.
>
> > + else
> > + attach_type = bpf_program__get_expected_attach_type(prog);
> > +
> > + link_fd = bpf_link_create(prog_fd, target_fd, attach_type, &opts);
> > if (link_fd < 0) {
> > link_fd = -errno;
> > free(link);
> > @@ -9357,19 +9363,25 @@ bpf_program__attach_fd(struct bpf_program *prog, int target_fd,
> > struct bpf_link *
> > bpf_program__attach_cgroup(struct bpf_program *prog, int cgroup_fd)
> > {
> > - return bpf_program__attach_fd(prog, cgroup_fd, "cgroup");
> > + return bpf_program__attach_fd(prog, cgroup_fd, 0, "cgroup");
> > }
> >
> > struct bpf_link *
> > bpf_program__attach_netns(struct bpf_program *prog, int netns_fd)
> > {
> > - return bpf_program__attach_fd(prog, netns_fd, "netns");
> > + return bpf_program__attach_fd(prog, netns_fd, 0, "netns");
> > }
> >
> > struct bpf_link *bpf_program__attach_xdp(struct bpf_program *prog, int ifindex)
> > {
> > /* target_fd/target_ifindex use the same field in LINK_CREATE */
> > - return bpf_program__attach_fd(prog, ifindex, "xdp");
> > + return bpf_program__attach_fd(prog, ifindex, 0, "xdp");
> > +}
> > +
> > +struct bpf_link *bpf_program__attach_freplace(struct bpf_program *prog,
> > + int target_fd, int target_btf_id)
> > +{
> > + return bpf_program__attach_fd(prog, target_fd, target_btf_id, "freplace");
> > }
> >
> > struct bpf_link *
> > diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> > index a750f67a23f6..ce5add9b9203 100644
> > --- a/tools/lib/bpf/libbpf.h
> > +++ b/tools/lib/bpf/libbpf.h
> > @@ -261,6 +261,9 @@ LIBBPF_API struct bpf_link *
> > bpf_program__attach_netns(struct bpf_program *prog, int netns_fd);
> > LIBBPF_API struct bpf_link *
> > bpf_program__attach_xdp(struct bpf_program *prog, int ifindex);
> > +LIBBPF_API struct bpf_link *
> > +bpf_program__attach_freplace(struct bpf_program *prog,
> > + int target_fd, int target_btf_id);
>
> maybe a const char * function name instead of target_btf_id would be a
> nicer API? Users won't have to deal with fetching target prog's BTF,
> searching it, etc. That's all pretty straightforward for libbpf to do,
> leaving users with more natural and simpler API.
>
bpf_program__set_attach_target() uses string name for target
functions, we should definitely be consistent here
> >
> > struct bpf_map;
> >
> > diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
> > index 92ceb48a5ca2..3cc2c42f435d 100644
> > --- a/tools/lib/bpf/libbpf.map
> > +++ b/tools/lib/bpf/libbpf.map
> > @@ -302,6 +302,7 @@ LIBBPF_0.1.0 {
> >
> > LIBBPF_0.2.0 {
> > global:
> > + bpf_program__attach_freplace;
> > bpf_program__section_name;
> > perf_buffer__buffer_cnt;
> > perf_buffer__buffer_fd;
> >
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