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Miller" , Daniel Borkmann , Andrii Nakryiko , Networking , bpf , Kernel Team Subject: Re: [PATCH v2 bpf-next 09/16] libbpf: Support for fd_idx Message-ID: <20210427025309.yma2vy4m4qbk5srv@ast-mbp.dhcp.thefacebook.com> References: <20210423002646.35043-1-alexei.starovoitov@gmail.com> <20210423002646.35043-10-alexei.starovoitov@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Mon, Apr 26, 2021 at 10:14:45AM -0700, Andrii Nakryiko wrote: > On Thu, Apr 22, 2021 at 5:27 PM Alexei Starovoitov > wrote: > > > > From: Alexei Starovoitov > > > > Add support for FD_IDX make libbpf prefer that approach to loading programs. > > > > Signed-off-by: Alexei Starovoitov > > --- > > tools/lib/bpf/bpf.c | 1 + > > tools/lib/bpf/libbpf.c | 70 +++++++++++++++++++++++++++++---- > > tools/lib/bpf/libbpf_internal.h | 1 + > > 3 files changed, 65 insertions(+), 7 deletions(-) > > > > [...] > > > +static int probe_kern_fd_idx(void) > > +{ > > + struct bpf_load_program_attr attr; > > + struct bpf_insn insns[] = { > > + BPF_LD_IMM64_RAW(BPF_REG_0, BPF_PSEUDO_MAP_IDX, 0), > > + BPF_EXIT_INSN(), > > + }; > > + > > + memset(&attr, 0, sizeof(attr)); > > + attr.prog_type = BPF_PROG_TYPE_SOCKET_FILTER; > > + attr.insns = insns; > > + attr.insns_cnt = ARRAY_SIZE(insns); > > + attr.license = "GPL"; > > + > > + probe_fd(bpf_load_program_xattr(&attr, NULL, 0)); > > probe_fd() calls close(fd) internally, which technically can interfere > with errno, though close() shouldn't be called because syscall has to > fail on correct kernels... So this should work, but I feel like > open-coding that logic is better than ignoring probe_fd() result. It will fail on all kernels. That probe_fd was a left over of earlier detection approach where it would proceed to load all the way, but then I switched to: > > + return errno == EPROTO; since such style of probing is much cheaper for the kernel and user space. But point taken. Will open code it. > > +} > > + > > [...] > > > @@ -7239,6 +7279,8 @@ bpf_object__load_progs(struct bpf_object *obj, int log_level) > > struct bpf_program *prog; > > size_t i; > > int err; > > + struct bpf_map *map; > > + int *fd_array = NULL; > > > > for (i = 0; i < obj->nr_programs; i++) { > > prog = &obj->programs[i]; > > @@ -7247,6 +7289,16 @@ bpf_object__load_progs(struct bpf_object *obj, int log_level) > > return err; > > } > > > > + if (kernel_supports(FEAT_FD_IDX) && obj->nr_maps) { > > + fd_array = malloc(sizeof(int) * obj->nr_maps); > > + if (!fd_array) > > + return -ENOMEM; > > + for (i = 0; i < obj->nr_maps; i++) { > > + map = &obj->maps[i]; > > + fd_array[i] = map->fd; > > nit: obj->maps[i].fd will keep it a single line > > > + } > > + } > > + > > for (i = 0; i < obj->nr_programs; i++) { > > prog = &obj->programs[i]; > > if (prog_is_subprog(obj, prog)) > > @@ -7256,10 +7308,14 @@ bpf_object__load_progs(struct bpf_object *obj, int log_level) > > continue; > > } > > prog->log_level |= log_level; > > + prog->fd_array = fd_array; > > you are not freeing this memory on success, as far as I can see. hmm. there is free on success below. > And > given multiple programs are sharing fd_array, it's a bit problematic > for prog to have fd_array. This is per-object properly, so let's add > it at bpf_object level and clean it up on bpf_object__close()? And by > assigning to obj->fd_array at malloc() site, you won't need to do all > the error-handling free()s below. hmm. that sounds worse. why add another 8 byte to bpf_object that won't be used until this last step of bpf_object__load_progs. And only for the duration of this loading. It's cheaper to have this alloc here with two free()s below. > > > err = bpf_program__load(prog, obj->license, obj->kern_version); > > - if (err) > > + if (err) { > > + free(fd_array); > > return err; > > + } > > } > > + free(fd_array); > > return 0; > > } > > > > diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h > > index 6017902c687e..9114c7085f2a 100644 > > --- a/tools/lib/bpf/libbpf_internal.h > > +++ b/tools/lib/bpf/libbpf_internal.h > > @@ -204,6 +204,7 @@ struct bpf_prog_load_params { > > __u32 log_level; > > char *log_buf; > > size_t log_buf_sz; > > + int *fd_array; > > }; > > > > int libbpf__bpf_prog_load(const struct bpf_prog_load_params *load_attr); > > -- > > 2.30.2 > > --