On Thu, Jul 8, 2021 at 7:48 PM Shuyi Cheng <chengshuyi@xxxxxxxxxxxxxxxxx> wrote: > > btf_custom_path allows developers to load custom BTF, and subsequent > CO-RE will use custom BTF for relocation. > > Learn from Andrii's comments in [0], add the btf_custom_path parameter > to bpf_obj_open_opts, you can directly use the skeleton's > <objname>_bpf__open_opts function to pass in the btf_custom_path > parameter. > > Prior to this, there was also a developer who provided a patch with > similar functions. It is a pity that the follow-up did not continue to > advance. See [1]. > > [0]https://lore.kernel.org/bpf/CAEf4BzbJZLjNoiK8_VfeVg_Vrg=9iYFv+po-38SMe=UzwDKJ=Q@xxxxxxxxxxxxxx/#t > [1]https://yhbt.net/lore/all/CAEf4Bzbgw49w2PtowsrzKQNcxD4fZRE6AKByX-5-dMo-+oWHHA@xxxxxxxxxxxxxx/ > > Signed-off-by: Shuyi Cheng <chengshuyi@xxxxxxxxxxxxxxxxx> > --- > tools/lib/bpf/libbpf.c | 46 ++++++++++++++++++++++++++++++++++++++++++++-- > tools/lib/bpf/libbpf.h | 6 +++++- > 2 files changed, 49 insertions(+), 3 deletions(-) > > diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c > index 1e04ce7..6702b7f 100644 > --- a/tools/lib/bpf/libbpf.c > +++ b/tools/lib/bpf/libbpf.c > @@ -498,6 +498,10 @@ struct bpf_object { > * it at load time. > */ > struct btf *btf_vmlinux; > + /* custom BTF is in addition to vmlinux BTF (i.e., Use the CO-RE > + * feature in the old kernel). > + */ nit: "path to custom BTF used for CO-RE relocations" as a description? > + char *btf_custom_path; > /* vmlinux BTF override for CO-RE relocations */ > struct btf *btf_vmlinux_override; > /* Lazily initialized kernel module BTFs */ > @@ -2668,6 +2672,27 @@ static bool obj_needs_vmlinux_btf(const struct bpf_object *obj) > return false; > } > > +static int bpf_object__load_override_btf(struct bpf_object *obj) > +{ > + int err; > + > + if (obj->btf_vmlinux_override) > + return 0; > + > + if (!obj->btf_custom_path) > + return 0; > + > + obj->btf_vmlinux_override = btf__parse(obj->btf_custom_path, NULL); > + err = libbpf_get_error(obj->btf_vmlinux_override); > + pr_debug("loading custom BTF '%s': %d\n", obj->btf_custom_path, err); > + if (err) { > + pr_warn("failed to parse custom BTF\n"); > + obj->btf_vmlinux_override = NULL; > + } > + > + return err; > +} see below, I don't think we need this function > + > static int bpf_object__load_vmlinux_btf(struct bpf_object *obj, bool force) > { > int err; > @@ -7554,7 +7579,7 @@ int bpf_program__load(struct bpf_program *prog, char *license, __u32 kern_ver) > __bpf_object__open(const char *path, const void *obj_buf, size_t obj_buf_sz, > const struct bpf_object_open_opts *opts) > { > - const char *obj_name, *kconfig; > + const char *obj_name, *kconfig, *btf_tmp_path; > struct bpf_program *prog; > struct bpf_object *obj; > char tmp_name[64]; > @@ -7584,6 +7609,19 @@ int bpf_program__load(struct bpf_program *prog, char *license, __u32 kern_ver) > obj = bpf_object__new(path, obj_buf, obj_buf_sz, obj_name); > if (IS_ERR(obj)) > return obj; > + > + btf_tmp_path = OPTS_GET(opts, btf_custom_path, NULL); > + if (btf_tmp_path) { > + if (strlen(btf_tmp_path) >= PATH_MAX) { > + err = -ENAMETOOLONG; > + goto out; > + } > + obj->btf_custom_path = strdup(btf_tmp_path); > + if (!obj->btf_custom_path) { > + err = -ENOMEM; > + goto out; > + } > + } this part looks good > > kconfig = OPTS_GET(opts, kconfig, NULL); > if (kconfig) { > @@ -8049,6 +8087,7 @@ int bpf_object__load_xattr(struct bpf_object_load_attr *attr) > bpf_gen__init(obj->gen_loader, attr->log_level); > > err = bpf_object__probe_loading(obj); > + err = err ? : bpf_object__load_override_btf(obj); btf_vmlinux_override is already working properly, so all you need to do here (once you remembered btf_custom_path) is to pass it to bpf_object__relocate. All the rest is taken care of, so you don't need to add extra cleanup (except for zfree(btf_custom_path)). > err = err ? : bpf_object__load_vmlinux_btf(obj, false); > err = err ? : bpf_object__resolve_externs(obj, obj->kconfig); > err = err ? : bpf_object__sanitize_and_load_btf(obj); so few lines below this code, after bpf_object__create_maps(obj): err = err ? : bpf_object__relocate(obj, obj->btf_custom_path ?: attr->target_btf_path); This way open_opts->btf_custom_path serves as an override for load_attr's target_btf_path (which we are going to deprecate anyways). The only remaining thing is to make sure that bpf_object__load_vmlinux_btf() won't attempt to load real vmlinux BTF *just for CO-RE*. So in obj_needs_vmlinux_btf() make sure to not return true for CO-RE relocations if custom_btf_path is specified (see Vamsi's patch which has this logic already). > @@ -8075,9 +8114,11 @@ int bpf_object__load_xattr(struct bpf_object_load_attr *attr) > } > free(obj->btf_modules); > > - /* clean up vmlinux BTF */ > + /* clean up vmlinux BTF and custom BTF*/ > btf__free(obj->btf_vmlinux); > obj->btf_vmlinux = NULL; > + btf__free(obj->btf_vmlinux_override); > + obj->btf_vmlinux_override = NULL; this shouldn't be necessary, bpf_object__relocate_core() handled this > > obj->loaded = true; /* doesn't matter if successfully or not */ > > @@ -8702,6 +8743,7 @@ void bpf_object__close(struct bpf_object *obj) > for (i = 0; i < obj->nr_maps; i++) > bpf_map__destroy(&obj->maps[i]); > > + zfree(&obj->btf_custom_path); > zfree(&obj->kconfig); > zfree(&obj->externs); > obj->nr_extern = 0; > diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h > index 6e61342..5002d1f 100644 > --- a/tools/lib/bpf/libbpf.h > +++ b/tools/lib/bpf/libbpf.h > @@ -94,8 +94,12 @@ struct bpf_object_open_opts { > * system Kconfig for CONFIG_xxx externs. > */ > const char *kconfig; > + /* custom BTF is in addition to vmlinux BTF (i.e., Use the CO-RE > + * feature in the old kernel). Instead of "Use the CO-RE feature in the old kernel", let's point out explicitly that this custom BTF is used *only* for CO-RE, and any other feature that relies on kernel BTF will still need actual vmlinux BTF. Something like this: /* Path to the custom BTF to be used for BPF CO-RE relocations. * This custom BTF completely replaces the use of vmlinux BTF * for the purpose of CO-RE relocations. * NOTE: any other BPF feature (e.g., fentry/fexit programs, * struct_ops, etc) will need actual kernel BTF at /sys/kernel/btf/vmlinux. */ I think this will make it much clearer what's the intended purpose here. > + */ > + char *btf_custom_path; > }; > -#define bpf_object_open_opts__last_field kconfig > +#define bpf_object_open_opts__last_field btf_custom_path > > LIBBPF_API struct bpf_object *bpf_object__open(const char *path); > LIBBPF_API struct bpf_object * > -- > 1.8.3.1 >
