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Date: Tue, 5 Feb 2019 14:34:56 -0800
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Yonghong Song <yhs@...com>
Cc: 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>
Subject: Re: [PATCH bpf-next 1/2] btf: separate btf creation and loading
On Tue, Feb 5, 2019 at 1:25 PM Yonghong Song <yhs@...com> wrote:
>
>
>
> 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.
I though it would be convenient to get created fd back from
btf_load(), but I don't have strong preferences. In any case, we have
btf__get_fd() to get it back, so I will change btf__load() to return
just error code.
>
> > + 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,
Yep, will fix to be alphabetically sorted.
>
>
> > btf__get_map_kv_tids;
> > btf__get_nr_types;
> > btf__get_strings;
> >
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