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[85.204.121.218]) by smtp.gmail.com with ESMTPSA id o11sm6363207lfl.48.2019.10.29.11.44.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 29 Oct 2019 11:44:53 -0700 (PDT) Received: by alrua-x1.borgediget.toke.dk (Postfix, from userid 1000) id AC3001818B6; Tue, 29 Oct 2019 19:44:52 +0100 (CET) From: Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= To: Andrii Nakryiko Cc: Daniel Borkmann , Alexei Starovoitov , Martin KaFai Lau , Song Liu , Yonghong Song , Jesper Dangaard Brouer , David Miller , Networking , bpf Subject: Re: [PATCH bpf-next v3 3/4] libbpf: Add auto-pinning of maps when loading BPF objects In-Reply-To: References: <157220959547.48922.6623938299823744715.stgit@toke.dk> <157220959873.48922.4763375792594816553.stgit@toke.dk> <877e4nsxth.fsf@toke.dk> X-Clacks-Overhead: GNU Terry Pratchett Date: Tue, 29 Oct 2019 19:44:52 +0100 Message-ID: <878sp3qtln.fsf@toke.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org Andrii Nakryiko writes: > On Tue, Oct 29, 2019 at 2:30 AM Toke Høiland-Jørgensen wrote: >> >> Andrii Nakryiko writes: >> >> > On Sun, Oct 27, 2019 at 1:53 PM Toke Høiland-Jørgensen wrote: >> >> >> >> From: Toke Høiland-Jørgensen >> >> >> >> This adds support to libbpf for setting map pinning information as part of >> >> the BTF map declaration, to get automatic map pinning (and reuse) on load. >> >> The pinning type currently only supports a single PIN_BY_NAME mode, where >> >> each map will be pinned by its name in a path that can be overridden, but >> >> defaults to /sys/fs/bpf. >> >> >> >> Since auto-pinning only does something if any maps actually have a >> >> 'pinning' BTF attribute set, we default the new option to enabled, on the >> >> assumption that seamless pinning is what most callers want. >> >> >> >> When a map has a pin_path set at load time, libbpf will compare the map >> >> pinned at that location (if any), and if the attributes match, will re-use >> >> that map instead of creating a new one. If no existing map is found, the >> >> newly created map will instead be pinned at the location. >> >> >> >> Programs wanting to customise the pinning can override the pinning paths >> >> using bpf_map__set_pin_path() before calling bpf_object__load() (including >> >> setting it to NULL to disable pinning of a particular map). >> >> >> >> Signed-off-by: Toke Høiland-Jørgensen >> >> --- >> >> tools/lib/bpf/bpf_helpers.h | 6 ++ >> >> tools/lib/bpf/libbpf.c | 142 ++++++++++++++++++++++++++++++++++++++++++- >> >> tools/lib/bpf/libbpf.h | 11 +++ >> >> 3 files changed, 154 insertions(+), 5 deletions(-) >> >> >> > >> > [...] >> > >> >> >> >> -static int bpf_object__init_maps(struct bpf_object *obj, bool relaxed_maps) >> >> +static int bpf_object__build_map_pin_paths(struct bpf_object *obj, >> >> + const char *path) >> >> +{ >> >> + struct bpf_map *map; >> >> + >> >> + if (!path) >> >> + path = "/sys/fs/bpf"; >> >> + >> >> + bpf_object__for_each_map(map, obj) { >> >> + char buf[PATH_MAX]; >> >> + int err, len; >> >> + >> >> + if (map->pinning != LIBBPF_PIN_BY_NAME) >> >> + continue; >> > >> > still think it's better be done from map definition parsing code >> > instead of a separate path, which will ignore most of maps anyways (of >> > course by extracting this whole buffer creation logic into a >> > function). >> >> Hmm, okay, can do that. I think we should still store the actual value >> of the 'pinning' attribute, though; and even have a getter for it. The >> app may want to do something with that information instead of having to >> infer it from map->pin_path. Certainly when we add other values of the >> pinning attribute, but we may as well add the API to get the value >> now... > > Let's now expose more stuff than what we need to expose. If we really > will have a need for that, it's really easy to add. Right now you > won't even need to store pinning attribute in bpf_map, because you'll > be just setting proper pin_path in init_user_maps(), as suggested > above. While I do think it's a bit weird that there's an attribute you can set but can't get at, I will grudgingly admit that it's not strictly needed right now... So OK, I'll leave it out :) >> >> + >> >> + len = snprintf(buf, PATH_MAX, "%s/%s", path, bpf_map__name(map)); >> >> + if (len < 0) >> >> + return -EINVAL; >> >> + else if (len >= PATH_MAX) >> > >> > [...] >> > >> >> return 0; >> >> } >> >> >> >> +static bool map_is_reuse_compat(const struct bpf_map *map, >> >> + int map_fd) >> > >> > nit: this should fit on single line? >> > >> >> +{ >> >> + struct bpf_map_info map_info = {}; >> >> + char msg[STRERR_BUFSIZE]; >> >> + __u32 map_info_len; >> >> + >> >> + map_info_len = sizeof(map_info); >> >> + >> >> + if (bpf_obj_get_info_by_fd(map_fd, &map_info, &map_info_len)) { >> >> + pr_warn("failed to get map info for map FD %d: %s\n", >> >> + map_fd, libbpf_strerror_r(errno, msg, sizeof(msg))); >> >> + return false; >> >> + } >> >> + >> >> + return (map_info.type == map->def.type && >> >> + map_info.key_size == map->def.key_size && >> >> + map_info.value_size == map->def.value_size && >> >> + map_info.max_entries == map->def.max_entries && >> >> + map_info.map_flags == map->def.map_flags && >> >> + map_info.btf_key_type_id == map->btf_key_type_id && >> >> + map_info.btf_value_type_id == map->btf_value_type_id); >> > >> > If map was pinned by older version of the same app, key and value type >> > id are probably gonna be different, even if the type definition itself >> > it correct. We probably shouldn't check that? >> >> Oh, I thought the type IDs would stay relatively stable. If not then I >> agree that we shouldn't be checking them here. Will fix. > > type IDs are just an ordered index of a type, as generated by Clang. > No stability guarantees. Just adding extra typedef somewhere in > unrelated type might shift all the type IDs around. Ah, so it's just numbering types within the same translation unit? I thought it was somehow globally (or system-wide) unique (though not sure how I imagined that would be achieved, TBH). >> >> +} >> >> + >> >> +static int >> >> +bpf_object__reuse_map(struct bpf_map *map) >> >> +{ >> >> + char *cp, errmsg[STRERR_BUFSIZE]; >> >> + int err, pin_fd; >> >> + >> >> + pin_fd = bpf_obj_get(map->pin_path); >> >> + if (pin_fd < 0) { >> >> + if (errno == ENOENT) { >> >> + pr_debug("found no pinned map to reuse at '%s'\n", >> >> + map->pin_path); >> >> + return 0; >> >> + } >> >> + >> >> + cp = libbpf_strerror_r(errno, errmsg, sizeof(errmsg)); >> >> + pr_warn("couldn't retrieve pinned map '%s': %s\n", >> >> + map->pin_path, cp); >> >> + return -errno; >> > >> > store errno locally >> >> *shrugs* okay, if you insist... > > I guess I do insist on correct handling of errno, instead of > potentially returning garbage value from some unrelated syscall from > inside of pr_warn's user-provided callback. > > Even libbpf_strerror_r can garble errno (e.g., through its strerror_r > call), so make sure you store it before passing into > libbpf_strerror_r(). Ohh, right, didn't think about those having side effects; then your worry makes more sense. I thought you were just being pedantic, which is why I was being grumpy (did change it, though) :) >> >> >> + } >> >> + >> >> + if (!map_is_reuse_compat(map, pin_fd)) { >> >> + pr_warn("couldn't reuse pinned map at '%s': " >> >> + "parameter mismatch\n", map->pin_path); >> >> + close(pin_fd); >> >> + return -EINVAL; >> >> + } >> >> + >> >> + err = bpf_map__reuse_fd(map, pin_fd); >> >> + if (err) { >> >> + close(pin_fd); >> >> + return err; >> >> + } >> >> + map->pinned = true; >> >> + pr_debug("reused pinned map at '%s'\n", map->pin_path); >> >> + >> >> + return 0; >> >> +} >> >> + >> > >> > [...] >> > >> >> +enum libbpf_pin_type { >> >> + LIBBPF_PIN_NONE, >> >> + /* PIN_BY_NAME: pin maps by name (in /sys/fs/bpf by default) */ >> >> + LIBBPF_PIN_BY_NAME, >> >> +}; >> >> + >> >> LIBBPF_API int bpf_object__pin_maps(struct bpf_object *obj, const char *path); >> > >> > pin_maps should take into account opts->auto_pin_path, shouldn't it? >> > >> > Which is why I also think that auto_pin_path is bad name, because it's >> > not only for auto-pinning, it's a pinning root path, so something like >> > pin_root_path or just pin_root is better and less misleading name. >> >> I view auto_pin_path as something that is used specifically for the >> automatic pinning based on the 'pinning' attribute. Any other use of >> pinning is for custom use and the user can pass a custom pin path to >> those functions. > > What's the benefit of restricting it to just this use case? If app > wants to use something other than /sys/fs/bpf as a default root path, > why would that be restricted only to auto-pinned maps? It seems to me > that having set this on bpf_object__open() and then calling > bpf_object__pin_maps(NULL) should just take this overridden root path > into account. Isn't that a logical behavior? No, I think the logical behaviour is for pin_maps(NULL) to just pin all maps at map->pin_path if set (and same for unpin). Already changed it to this behaviour, actually. -Toke