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Message-ID: <87wo7b49mn.fsf@toke.dk>
Date: Mon, 23 Mar 2020 12:02:24 +0100
From: Toke Høiland-Jørgensen <toke@...hat.com>
To: Andrii Nakryiko <andriin@...com>, bpf@...r.kernel.org,
netdev@...r.kernel.org, ast@...com, daniel@...earbox.net
Cc: andrii.nakryiko@...il.com, kernel-team@...com,
Andrii Nakryiko <andriin@...com>
Subject: Re: [PATCH bpf-next 5/6] libbpf: add support for bpf_link-based cgroup attachment
Andrii Nakryiko <andriin@...com> writes:
> Add bpf_program__attach_cgroup(), which uses BPF_LINK_CREATE subcommand to
> create an FD-based kernel bpf_link. Also add low-level bpf_link_create() API.
>
> If expected_attach_type is not specified explicitly with
> bpf_program__set_expected_attach_type(), libbpf will try to determine proper
> attach type from BPF program's section definition.
>
> Also add support for bpf_link's underlying BPF program replacement:
> - unconditional through high-level bpf_link__update_program() API;
> - cmpxchg-like with specifying expected current BPF program through
> low-level bpf_link_update() API.
>
> Signed-off-by: Andrii Nakryiko <andriin@...com>
> ---
> tools/include/uapi/linux/bpf.h | 12 +++++++++
> tools/lib/bpf/bpf.c | 34 +++++++++++++++++++++++++
> tools/lib/bpf/bpf.h | 19 ++++++++++++++
> tools/lib/bpf/libbpf.c | 46 ++++++++++++++++++++++++++++++++++
> tools/lib/bpf/libbpf.h | 8 +++++-
> tools/lib/bpf/libbpf.map | 4 +++
> 6 files changed, 122 insertions(+), 1 deletion(-)
>
> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> index fad9f79bb8f1..fa944093f9fc 100644
> --- a/tools/include/uapi/linux/bpf.h
> +++ b/tools/include/uapi/linux/bpf.h
> @@ -112,6 +112,7 @@ enum bpf_cmd {
> BPF_MAP_UPDATE_BATCH,
> BPF_MAP_DELETE_BATCH,
> BPF_LINK_CREATE,
> + BPF_LINK_UPDATE,
> };
>
> enum bpf_map_type {
> @@ -574,6 +575,17 @@ union bpf_attr {
> __u32 target_fd; /* object to attach to */
> __u32 attach_type; /* attach type */
> } link_create;
> +
> + struct { /* struct used by BPF_LINK_UPDATE command */
> + __u32 link_fd; /* link fd */
> + /* new program fd to update link with */
> + __u32 new_prog_fd;
> + __u32 flags; /* extra flags */
> + /* expected link's program fd; is specified only if
> + * BPF_F_REPLACE flag is set in flags */
> + __u32 old_prog_fd;
> + } link_update;
> +
> } __attribute__((aligned(8)));
>
> /* The description below is an attempt at providing documentation to eBPF
> diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
> index c6dafe563176..35c34fc81bd0 100644
> --- a/tools/lib/bpf/bpf.c
> +++ b/tools/lib/bpf/bpf.c
> @@ -584,6 +584,40 @@ int bpf_prog_detach2(int prog_fd, int target_fd, enum bpf_attach_type type)
> return sys_bpf(BPF_PROG_DETACH, &attr, sizeof(attr));
> }
>
> +int bpf_link_create(int prog_fd, int target_fd,
> + enum bpf_attach_type attach_type,
> + const struct bpf_link_create_opts *opts)
> +{
> + union bpf_attr attr;
> +
> + if (!OPTS_VALID(opts, bpf_link_create_opts))
> + return -EINVAL;
> +
> + memset(&attr, 0, sizeof(attr));
> + attr.link_create.prog_fd = prog_fd;
> + attr.link_create.target_fd = target_fd;
> + attr.link_create.attach_type = attach_type;
> +
> + return sys_bpf(BPF_LINK_CREATE, &attr, sizeof(attr));
> +}
> +
> +int bpf_link_update(int link_fd, int new_prog_fd,
> + const struct bpf_link_update_opts *opts)
> +{
> + union bpf_attr attr;
> +
> + if (!OPTS_VALID(opts, bpf_link_update_opts))
> + return -EINVAL;
> +
> + memset(&attr, 0, sizeof(attr));
> + attr.link_update.link_fd = link_fd;
> + attr.link_update.new_prog_fd = new_prog_fd;
> + attr.link_update.flags = OPTS_GET(opts, flags, 0);
> + attr.link_update.old_prog_fd = OPTS_GET(opts, old_prog_fd, 0);
> +
> + return sys_bpf(BPF_LINK_UPDATE, &attr, sizeof(attr));
> +}
> +
> int bpf_prog_query(int target_fd, enum bpf_attach_type type, __u32 query_flags,
> __u32 *attach_flags, __u32 *prog_ids, __u32 *prog_cnt)
> {
> diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
> index b976e77316cc..46d47afdd887 100644
> --- a/tools/lib/bpf/bpf.h
> +++ b/tools/lib/bpf/bpf.h
> @@ -168,6 +168,25 @@ LIBBPF_API int bpf_prog_detach(int attachable_fd, enum bpf_attach_type type);
> LIBBPF_API int bpf_prog_detach2(int prog_fd, int attachable_fd,
> enum bpf_attach_type type);
>
> +struct bpf_link_create_opts {
> + size_t sz; /* size of this struct for forward/backward compatibility */
> +};
> +#define bpf_link_create_opts__last_field sz
> +
> +LIBBPF_API int bpf_link_create(int prog_fd, int target_fd,
> + enum bpf_attach_type attach_type,
> + const struct bpf_link_create_opts *opts);
> +
> +struct bpf_link_update_opts {
> + size_t sz; /* size of this struct for forward/backward compatibility */
> + __u32 flags; /* extra flags */
> + __u32 old_prog_fd; /* expected old program FD */
> +};
> +#define bpf_link_update_opts__last_field old_prog_fd
> +
> +LIBBPF_API int bpf_link_update(int link_fd, int new_prog_fd,
> + const struct bpf_link_update_opts *opts);
> +
> struct bpf_prog_test_run_attr {
> int prog_fd;
> int repeat;
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 085e41f9b68e..8b23c70033d3 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -6951,6 +6951,12 @@ struct bpf_link {
> bool disconnected;
> };
>
> +/* Replace link's underlying BPF program with the new one */
> +int bpf_link__update_program(struct bpf_link *link, struct bpf_program *prog)
> +{
> + return bpf_link_update(bpf_link__fd(link), bpf_program__fd(prog), NULL);
> +}
I would expect bpf_link to keep track of the previous program and
automatically fill it in with this operation. I.e., it should be
possible to do something like:
link = bpf_link__open("/sys/fs/bpf/my_link");
prog = bpf_link__get_prog(link);
new_prog = enhance_prog(prog);
err = bpf_link__update_program(link, new_prog);
and have atomic replacement "just work". This obviously implies that
bpf_link__open() should use that BPF_LINK_QUERY operation I was
requesting in my comment to the previous patch :)
-Toke
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