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Date: Tue, 5 Feb 2019 21:25:48 +0000
From: Yonghong Song <yhs@...com>
To: Andrii Nakryiko <andriin@...com>, Song Liu <songliubraving@...com>,
"Alexei Starovoitov" <ast@...com>, Martin Lau <kafai@...com>,
"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
"daniel@...earbox.net" <daniel@...earbox.net>,
"andrii.nakryiko@...il.com" <andrii.nakryiko@...il.com>
Subject: Re: [PATCH bpf-next 1/2] btf: separate btf creation and loading
On 2/5/19 11:48 AM, Andrii Nakryiko wrote:
> This change splits out previous btf__new functionality of constructing
> struct btf and loading it into kernel into two:
> - btf__new() just creates and initializes struct btf
> - btf__load() attempts to load existing struct btf into kernel
>
> btf__free will still close BTF fd, if it was ever loaded successfully
> into kernel.
>
> This change allows users of libbpf to manipulate BTF using its API,
> without the need to unnecessarily load it into kernel.
>
> One of the intended use cases is pahole using libbpf to do DWARF to BTF
> conversion and deduplication using libbpf, while handling ELF sections
> overwrites and other concerns on its own.
>
> Signed-off-by: Andrii Nakryiko <andriin@...com>
> Acked-by: Song Liu <songliubraving@...com>
> ---
> tools/lib/bpf/btf.c | 53 ++++++++++++++++++++++------------------
> tools/lib/bpf/btf.h | 1 +
> tools/lib/bpf/libbpf.c | 2 +-
> tools/lib/bpf/libbpf.map | 1 +
> 4 files changed, 32 insertions(+), 25 deletions(-)
>
> diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
> index 4949f8840bda..065d51fa63e5 100644
> --- a/tools/lib/bpf/btf.c
> +++ b/tools/lib/bpf/btf.c
> @@ -366,8 +366,6 @@ void btf__free(struct btf *btf)
>
> struct btf *btf__new(__u8 *data, __u32 size)
> {
> - __u32 log_buf_size = 0;
> - char *log_buf = NULL;
> struct btf *btf;
> int err;
>
> @@ -377,15 +375,6 @@ struct btf *btf__new(__u8 *data, __u32 size)
>
> btf->fd = -1;
>
> - log_buf = malloc(BPF_LOG_BUF_SIZE);
> - if (!log_buf) {
> - err = -ENOMEM;
> - goto done;
> - }
> -
> - *log_buf = 0;
> - log_buf_size = BPF_LOG_BUF_SIZE;
> -
> btf->data = malloc(size);
> if (!btf->data) {
> err = -ENOMEM;
> @@ -395,17 +384,6 @@ struct btf *btf__new(__u8 *data, __u32 size)
> memcpy(btf->data, data, size);
> btf->data_size = size;
>
> - btf->fd = bpf_load_btf(btf->data, btf->data_size,
> - log_buf, log_buf_size, false);
> -
> - if (btf->fd == -1) {
> - err = -errno;
> - pr_warning("Error loading BTF: %s(%d)\n", strerror(errno), errno);
> - if (log_buf && *log_buf)
> - pr_warning("%s\n", log_buf);
> - goto done;
> - }
> -
> err = btf_parse_hdr(btf);
> if (err)
> goto done;
> @@ -417,8 +395,6 @@ struct btf *btf__new(__u8 *data, __u32 size)
> err = btf_parse_type_sec(btf);
>
> done:
> - free(log_buf);
> -
> if (err) {
> btf__free(btf);
> return ERR_PTR(err);
> @@ -427,6 +403,35 @@ struct btf *btf__new(__u8 *data, __u32 size)
> return btf;
> }
>
> +int btf__load(struct btf* btf) {
> + __u32 log_buf_size = BPF_LOG_BUF_SIZE;
> + char *log_buf = NULL;
> +
> + if (btf->fd >= 0) {
> + return -EEXIST;
> + }
> +
> + log_buf = malloc(log_buf_size);
> + if (!log_buf)
> + return -ENOMEM;
> +
> + *log_buf = 0;
> +
> + btf->fd = bpf_load_btf(btf->data, btf->data_size,
> + log_buf, log_buf_size, false);
> + if (btf->fd < 0) {
> + btf->fd = -errno;
Why you set btf->fd = -errno? Do you have any intended use for it later.
If not, I would still prefer the existing value -1. This will be
consistent with all other fd field convention in libbpf.
> + pr_warning("Error loading BTF: %s(%d)\n", strerror(errno), errno);
> + if (*log_buf)
> + pr_warning("%s\n", log_buf);
> + goto done;
> + }
> +
> +done:
> + free(log_buf);
> + return btf->fd;
> +}
> +
> int btf__fd(const struct btf *btf)
> {
> return btf->fd;
> diff --git a/tools/lib/bpf/btf.h b/tools/lib/bpf/btf.h
> index 25a9d2db035d..e8410887f93a 100644
> --- a/tools/lib/bpf/btf.h
> +++ b/tools/lib/bpf/btf.h
> @@ -57,6 +57,7 @@ struct btf_ext_header {
>
> LIBBPF_API void btf__free(struct btf *btf);
> LIBBPF_API struct btf *btf__new(__u8 *data, __u32 size);
> +LIBBPF_API int btf__load(struct btf* btf);
> LIBBPF_API __s32 btf__find_by_name(const struct btf *btf,
> const char *type_name);
> LIBBPF_API __u32 btf__get_nr_types(const struct btf *btf);
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 47969aa0faf8..75b82c1cfc72 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -835,7 +835,7 @@ static int bpf_object__elf_collect(struct bpf_object *obj, int flags)
> obj->efile.maps_shndx = idx;
> else if (strcmp(name, BTF_ELF_SEC) == 0) {
> obj->btf = btf__new(data->d_buf, data->d_size);
> - if (IS_ERR(obj->btf)) {
> + if (IS_ERR(obj->btf) || btf__load(obj->btf) < 0) {
> pr_warning("Error loading ELF section %s: %ld. Ignored and continue.\n",
> BTF_ELF_SEC, PTR_ERR(obj->btf));
> obj->btf = NULL;
> diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
> index 89c1149e32ee..ffa1fe044f6a 100644
> --- a/tools/lib/bpf/libbpf.map
> +++ b/tools/lib/bpf/libbpf.map
> @@ -134,6 +134,7 @@ LIBBPF_0.0.2 {
> bpf_object__find_map_fd_by_name;
> bpf_get_link_xdp_id;
> btf__dedup;
> + btf__load;
Maybe put btf__load after btf__get_strings based on alphabetical order.
With the above changes,
> btf__get_map_kv_tids;
> btf__get_nr_types;
> btf__get_strings;
>
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