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Message-ID: <CAEf4BzZqEZLt0_qgmniY-hqgEg7q0ur0Z5U0r8KFTwSz=2StSg@mail.gmail.com>
Date: Thu, 22 Jul 2021 17:39:43 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Quentin Monnet <quentin@...valent.com>
Cc: Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Andrii Nakryiko <andrii@...nel.org>,
Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
John Fastabend <john.fastabend@...il.com>
Subject: Re: [PATCH bpf-next v2 2/5] libbpf: rename btf__get_from_id() as btf__load_from_kernel_by_id()
On Wed, Jul 21, 2021 at 8:38 AM Quentin Monnet <quentin@...valent.com> wrote:
>
> Rename function btf__get_from_id() as btf__load_from_kernel_by_id() to
> better indicate what the function does. Change the new function so that,
> instead of requiring a pointer to the pointer to update and returning
> with an error code, it takes a single argument (the id of the BTF
> object) and returns the corresponding pointer. This is more in line with
> the existing constructors.
>
> The other tools calling the deprecated btf__get_from_id() function will
> be updated in a future commit.
>
> References:
>
> - https://github.com/libbpf/libbpf/issues/278
> - https://github.com/libbpf/libbpf/wiki/Libbpf:-the-road-to-v1.0#btfh-apis
>
> v2:
> - Instead of a simple renaming, change the new function to make it
> return the pointer to the btf struct.
> - API v0.5.0 instead of v0.6.0.
We generally keep such version changes to cover letters. It keeps each
individual commit clean and collects full history in the cover letter
which becomes a body of merge commit when the whole patch set is
applied. For next revision please consolidate the history in the cover
letter. Thanks!
>
> Signed-off-by: Quentin Monnet <quentin@...valent.com>
> Acked-by: John Fastabend <john.fastabend@...il.com>
> ---
> tools/lib/bpf/btf.c | 25 +++++++++++++++++--------
> tools/lib/bpf/btf.h | 1 +
> tools/lib/bpf/libbpf.c | 5 +++--
> tools/lib/bpf/libbpf.map | 1 +
> 4 files changed, 22 insertions(+), 10 deletions(-)
>
> diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
> index 7e0de560490e..6654bdee7ad7 100644
> --- a/tools/lib/bpf/btf.c
> +++ b/tools/lib/bpf/btf.c
> @@ -1383,21 +1383,30 @@ struct btf *btf_get_from_fd(int btf_fd, struct btf *base_btf)
> return btf;
> }
>
> +struct btf *btf__load_from_kernel_by_id(__u32 id)
> +{
> + struct btf *btf;
> + int btf_fd;
> +
> + btf_fd = bpf_btf_get_fd_by_id(id);
> + if (btf_fd < 0)
> + return ERR_PTR(-errno);
please use libbpf_err_ptr() for consistency, see
bpf_object__open_mem() for an example
> +
> + btf = btf_get_from_fd(btf_fd, NULL);
> + close(btf_fd);
> +
> + return libbpf_ptr(btf);
> +}
> +
> int btf__get_from_id(__u32 id, struct btf **btf)
> {
> struct btf *res;
> - int err, btf_fd;
> + int err;
>
> *btf = NULL;
> - btf_fd = bpf_btf_get_fd_by_id(id);
> - if (btf_fd < 0)
> - return libbpf_err(-errno);
> -
> - res = btf_get_from_fd(btf_fd, NULL);
> + res = btf__load_from_kernel_by_id(id);
> err = libbpf_get_error(res);
>
> - close(btf_fd);
> -
> if (err)
> return libbpf_err(err);
>
> diff --git a/tools/lib/bpf/btf.h b/tools/lib/bpf/btf.h
> index fd8a21d936ef..3db9446bc133 100644
> --- a/tools/lib/bpf/btf.h
> +++ b/tools/lib/bpf/btf.h
> @@ -68,6 +68,7 @@ LIBBPF_API const void *btf__get_raw_data(const struct btf *btf, __u32 *size);
> LIBBPF_API const char *btf__name_by_offset(const struct btf *btf, __u32 offset);
> LIBBPF_API const char *btf__str_by_offset(const struct btf *btf, __u32 offset);
> LIBBPF_API int btf__get_from_id(__u32 id, struct btf **btf);
> +LIBBPF_API struct btf *btf__load_from_kernel_by_id(__u32 id);
let's move this definition to after btf__parse() to keep all
"constructors" together (we can move btf__get_from_id() there for
completeness as well, I suppose).
> LIBBPF_API int btf__get_map_kv_tids(const struct btf *btf, const char *map_name,
> __u32 expected_key_size,
> __u32 expected_value_size,
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 242e97892043..eff005b1eba1 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -9576,8 +9576,8 @@ static int libbpf_find_prog_btf_id(const char *name, __u32 attach_prog_fd)
> {
> struct bpf_prog_info_linear *info_linear;
> struct bpf_prog_info *info;
> - struct btf *btf = NULL;
> int err = -EINVAL;
> + struct btf *btf;
>
> info_linear = bpf_program__get_prog_info_linear(attach_prog_fd, 0);
> err = libbpf_get_error(info_linear);
> @@ -9591,7 +9591,8 @@ static int libbpf_find_prog_btf_id(const char *name, __u32 attach_prog_fd)
> pr_warn("The target program doesn't have BTF\n");
> goto out;
> }
> - if (btf__get_from_id(info->btf_id, &btf)) {
> + btf = btf__load_from_kernel_by_id(info->btf_id);
> + if (libbpf_get_error(btf)) {
there seems to be a bug in existing code and you are keeping it. On
error err will be 0. Let's fix it. Same for above if (!info->btf_id),
please fix that as well while you are at it.
> pr_warn("Failed to get BTF of the program\n");
> goto out;
> }
> diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
> index f7d52d76ca3a..ca8cc7a7faad 100644
> --- a/tools/lib/bpf/libbpf.map
> +++ b/tools/lib/bpf/libbpf.map
> @@ -373,6 +373,7 @@ LIBBPF_0.5.0 {
> bpf_map__initial_value;
> bpf_map_lookup_and_delete_elem_flags;
> bpf_object__gen_loader;
> + btf__load_from_kernel_by_id;
> btf__load_into_kernel;
> btf_dump__dump_type_data;
> libbpf_set_strict_mode;
> --
> 2.30.2
>
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