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Message-ID: <CAEf4Bzb-CewiZhsGEmSNSCGHLKQiXFO3gS+cJgD1Tx_L_gpiMg@mail.gmail.com>
Date: Mon, 28 Oct 2019 11:24:18 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Toke Høiland-Jørgensen <toke@...hat.com>
Cc: Daniel Borkmann <daniel@...earbox.net>,
Alexei Starovoitov <ast@...nel.org>,
Martin KaFai Lau <kafai@...com>,
Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
Jesper Dangaard Brouer <brouer@...hat.com>,
David Miller <davem@...emloft.net>,
Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH bpf-next v3 2/4] libbpf: Store map pin path and status in
struct bpf_map
On Sun, Oct 27, 2019 at 1:53 PM Toke Høiland-Jørgensen <toke@...hat.com> wrote:
>
> From: Toke Høiland-Jørgensen <toke@...hat.com>
>
> Support storing and setting a pin path in struct bpf_map, which can be used
> for automatic pinning. Also store the pin status so we can avoid attempts
> to re-pin a map that has already been pinned (or reused from a previous
> pinning).
>
> Acked-by: Andrii Nakryiko <andriin@...com>
> Signed-off-by: Toke Høiland-Jørgensen <toke@...hat.com>
> ---
> tools/lib/bpf/libbpf.c | 115 ++++++++++++++++++++++++++++++++++++----------
> tools/lib/bpf/libbpf.h | 3 +
> tools/lib/bpf/libbpf.map | 3 +
> 3 files changed, 97 insertions(+), 24 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index ce5ef3ddd263..eb1c5e6ad4a3 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -226,6 +226,8 @@ struct bpf_map {
> void *priv;
> bpf_map_clear_priv_t clear_priv;
> enum libbpf_map_type libbpf_type;
> + char *pin_path;
> + bool pinned;
> };
>
> struct bpf_secdata {
> @@ -4025,47 +4027,118 @@ int bpf_map__pin(struct bpf_map *map, const char *path)
> char *cp, errmsg[STRERR_BUFSIZE];
> int err;
>
> - err = check_path(path);
> - if (err)
> - return err;
> -
> if (map == NULL) {
> pr_warn("invalid map pointer\n");
> return -EINVAL;
> }
>
> - if (bpf_obj_pin(map->fd, path)) {
> - cp = libbpf_strerror_r(errno, errmsg, sizeof(errmsg));
> - pr_warn("failed to pin map: %s\n", cp);
> - return -errno;
> + if (map->pinned) {
> + pr_warn("map already pinned\n");
it would be helpful to print the name of the map, otherwise user will
have to guess
> + return -EEXIST;
> + }
> +
> + if (path && map->pin_path && strcmp(path, map->pin_path)) {
> + pr_warn("map already has pin path '%s' different from '%s'\n",
> + map->pin_path, path);
here pin_path probably would be unique enough, but for consistency we
might want to print map name as well
> + return -EINVAL;
> + }
> +
> + if (!map->pin_path && !path) {
> + pr_warn("missing pin path\n");
and here?
> + return -EINVAL;
> }
>
> - pr_debug("pinned map '%s'\n", path);
> + if (!map->pin_path) {
> + map->pin_path = strdup(path);
> + if (!map->pin_path) {
> + err = -errno;
> + goto out_err;
> + }
> + }
There is a bit of repetition of if conditions, based on whether we
have map->pin_path set (which is the most critical piece we care
about), so that makes it a bit harder to follow what's going on. How
about this structure, would it make a bit clearer what the error
conditions are? Not insisting, though.
if (map->pin_path) {
if (path && strcmp(...))
bad, exit
else { /* no pin_path */
if (!path)
very bad, exit
map->pin_path = strdup(..)
if (!map->pin_path)
also bad, exit
}
> +
> + err = check_path(map->pin_path);
> + if (err)
> + return err;
> +
[...]
>
> +int bpf_map__set_pin_path(struct bpf_map *map, const char *path)
> +{
> + char *old = map->pin_path, *new;
> +
> + if (path) {
> + new = strdup(path);
> + if (!new)
> + return -errno;
> + } else {
> + new = NULL;
> + }
> +
> + map->pin_path = new;
> + if (old)
> + free(old);
you don't really need old, just free map->pin_path before setting it
to new. Also assigning new = NULL will simplify if above.
> +
> + return 0;
> +}
> +
> +const char *bpf_map__get_pin_path(struct bpf_map *map)
> +{
> + return map->pin_path;
> +}
> +
> +bool bpf_map__is_pinned(struct bpf_map *map)
> +{
> + return map->pinned;
> +}
> +
> int bpf_object__pin_maps(struct bpf_object *obj, const char *path)
> {
> struct bpf_map *map;
> @@ -4106,17 +4179,10 @@ int bpf_object__pin_maps(struct bpf_object *obj, const char *path)
I might have missed something the change in some other patch, but
shouldn't pin_maps ignore already pinned maps? Otherwise we'll be
generating unnecessary warnings?
>
> err_unpin_maps:
> while ((map = bpf_map__prev(map, obj))) {
> - char buf[PATH_MAX];
> - int len;
> -
> - len = snprintf(buf, PATH_MAX, "%s/%s", path,
> - bpf_map__name(map));
> - if (len < 0)
> - continue;
> - else if (len >= PATH_MAX)
> + if (!map->pin_path)
> continue;
>
> - bpf_map__unpin(map, buf);
> + bpf_map__unpin(map, NULL);
so this will unpin auto-pinned maps (from BTF-defined maps). Is that
the desired behavior? I guess it might be ok (if you can't pin all of
your maps, you should probably clean all of them up?), but just
bringing it up.
> }
>
> return err;
> @@ -4266,6 +4332,7 @@ void bpf_object__close(struct bpf_object *obj)
>
> for (i = 0; i < obj->nr_maps; i++) {
> zfree(&obj->maps[i].name);
> + zfree(&obj->maps[i].pin_path);
> if (obj->maps[i].clear_priv)
> obj->maps[i].clear_priv(&obj->maps[i],
> obj->maps[i].priv);
> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> index c63e2ff84abc..a514729c43f5 100644
> --- a/tools/lib/bpf/libbpf.h
> +++ b/tools/lib/bpf/libbpf.h
> @@ -385,6 +385,9 @@ LIBBPF_API int bpf_map__resize(struct bpf_map *map, __u32 max_entries);
> LIBBPF_API bool bpf_map__is_offload_neutral(const struct bpf_map *map);
> LIBBPF_API bool bpf_map__is_internal(const struct bpf_map *map);
> LIBBPF_API void bpf_map__set_ifindex(struct bpf_map *map, __u32 ifindex);
> +LIBBPF_API int bpf_map__set_pin_path(struct bpf_map *map, const char *path);
> +LIBBPF_API const char *bpf_map__get_pin_path(struct bpf_map *map);
> +LIBBPF_API bool bpf_map__is_pinned(struct bpf_map *map);
> LIBBPF_API int bpf_map__pin(struct bpf_map *map, const char *path);
> LIBBPF_API int bpf_map__unpin(struct bpf_map *map, const char *path);
>
> diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
> index d1473ea4d7a5..c24d4c01591d 100644
> --- a/tools/lib/bpf/libbpf.map
> +++ b/tools/lib/bpf/libbpf.map
> @@ -197,4 +197,7 @@ LIBBPF_0.0.6 {
> bpf_object__open_mem;
> bpf_program__get_expected_attach_type;
> bpf_program__get_type;
> + bpf_map__get_pin_path;
> + bpf_map__set_pin_path;
> + bpf_map__is_pinned;
> } LIBBPF_0.0.5;
>
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