Add support for a new ELF section ".kmod_btfs" that allows BPF programs
to declare which kernel modules need BTF loading. This avoids loading
all module BTFs and speeds up program load when only a subset of modules
is needed.
Specifically, this patch introduces two internal functions:
- bpf_object__collect_kmod_btf_names(): parses the ".kmod_btfs"
section and collects the declared module names.
- is_kmod_btf_needed(): determines whether a given module's BTF
should be loaded, allowing libbpf to skip unneeded modules.
Signed-off-by: Fuyu Zhao <[email protected]>
---
tools/lib/bpf/bpf_helpers.h | 14 +++++
tools/lib/bpf/libbpf.c | 106 ++++++++++++++++++++++++++++++++++++
2 files changed, 120 insertions(+)
diff --git a/tools/lib/bpf/bpf_helpers.h b/tools/lib/bpf/bpf_helpers.h
index 9d160b5b9c0e..171ea055cd32 100644
--- a/tools/lib/bpf/bpf_helpers.h
+++ b/tools/lib/bpf/bpf_helpers.h
@@ -188,6 +188,20 @@ enum libbpf_tristate {
TRI_MODULE = 2,
};
+/* Helper typedef for declaring kernel module names that need BTF loading.
+ *
+ * Usage: define an array in the ".kmod_btfs" ELF section to specify
+ * which modules need BTF loading:
+ *
+ * DEFINE_KMOD_BTFS(_needed_kmods)= { "module1", "module2", ... };
+ *
+ * This avoids unnecessary BTF loading and speeds up the BPF program
+ * load process.
+ */
+#define KMOD_NAME_LEN 64
+#define DEFINE_KMOD_BTFS(name) \
+ SEC(".kmod_btfs") char name[][KMOD_NAME_LEN]
+
#define __kconfig __attribute__((section(".kconfig")))
#define __ksym __attribute__((section(".ksyms")))
#define __kptr_untrusted __attribute__((btf_type_tag("kptr_untrusted")))
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 514e4e9daa82..9fe8a653e8b6 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -548,6 +548,7 @@ struct bpf_struct_ops {
#define STRUCT_OPS_SEC ".struct_ops"
#define STRUCT_OPS_LINK_SEC ".struct_ops.link"
#define ARENA_SEC ".addr_space.1"
+#define KMODS_BTFS_SEC ".kmod_btfs"
enum libbpf_map_type {
LIBBPF_MAP_UNSPEC,
@@ -703,6 +704,9 @@ enum bpf_object_state {
OBJ_LOADED,
};
+/* Should match the definition in bpf_helpers.h */
+#define KMOD_NAME_LEN 64
+
struct bpf_object {
char name[BPF_OBJ_NAME_LEN];
char license[64];
@@ -779,6 +783,14 @@ struct bpf_object {
char *token_path;
int token_fd;
+ /* kernel module BTFs to load, declared in ".kmod_btfs" ELF section */
+ struct {
+ char (*data)[KMOD_NAME_LEN];
+ size_t nr_names;
+ size_t nr_loaded;
+ struct hashmap *hashmap;
+ } *kmod_btfs;
+
char path[];
};
@@ -901,6 +913,75 @@ bpf_object__init_prog(struct bpf_object *obj, struct
bpf_program *prog,
return -ENOMEM;
}
+static size_t mod_name_hash_fn(long key, void *ctx)
+{
+ return str_hash((char *)key);
+}
+
+static bool mod_name_equal_fn(long key1, long key2, void *ctx)
+{
+ return strcmp((char *)key1, (char *)key2) == 0;
+}
+
+static int
+bpf_object__collect_kmod_btf_names(struct bpf_object *obj, Elf_Data *sec_data,
+ const char *sec_name)
+{
+ int module_cnt, i, err = 0;
+
+ if (obj->kmod_btfs) {
+ pr_warn("sec '%s': duplicate sections detected\n", sec_name);
+ return -EEXIST;
+ }
+
+ if (sec_data->d_size % KMOD_NAME_LEN != 0) {
+ pr_warn("sec '%s': size %zu should be multiple of %d\n",
+ sec_name, sec_data->d_size, KMOD_NAME_LEN);
+ return -EINVAL;
+ }
+
+ module_cnt = sec_data->d_size / KMOD_NAME_LEN;
+ obj->kmod_btfs = calloc(1, sizeof(*obj->kmod_btfs));
+ if (!obj->kmod_btfs)
+ return -ENOMEM;
+
+ obj->kmod_btfs->data = calloc(module_cnt, KMOD_NAME_LEN);
+ if (!obj->kmod_btfs->data) {
+ err = -ENOMEM;
+ goto err_out;
+ }
+ memcpy(obj->kmod_btfs->data, sec_data->d_buf, sec_data->d_size);
+
+ obj->kmod_btfs->hashmap = hashmap__new(mod_name_hash_fn,
+ mod_name_equal_fn, NULL);
+ if (IS_ERR(obj->kmod_btfs->hashmap)) {
+ err = PTR_ERR(obj->kmod_btfs->hashmap);
+ goto err_out;
+ }
+
+ for (i = 0; i < module_cnt; i++) {
+ obj->kmod_btfs->data[i][KMOD_NAME_LEN - 1] = '\0';
+ if (hashmap__find(obj->kmod_btfs->hashmap,
+ obj->kmod_btfs->data[i], NULL)) {
+ pr_warn("sec '%s': ignored duplicate module '%s'\n",
+ sec_name, obj->kmod_btfs->data[i]);
+ continue;
+ }
+ err = hashmap__set(obj->kmod_btfs->hashmap,
obj->kmod_btfs->data[i],
+ 0, NULL, NULL);
+ if (err)
+ goto err_out;
+ obj->kmod_btfs->nr_names++;
+ }
+ return 0;
+
+err_out:
+ hashmap__free(obj->kmod_btfs->hashmap);
+ zfree(&obj->kmod_btfs->data);
+ zfree(&obj->kmod_btfs);
+ return err;
+}
+
static int
bpf_object__add_programs(struct bpf_object *obj, Elf_Data *sec_data,
const char *sec_name, int sec_idx)
@@ -4034,6 +4115,10 @@ static int bpf_object__elf_collect(struct bpf_object
*obj)
memcpy(obj->jumptables_data, data->d_buf,
data->d_size);
obj->jumptables_data_sz = data->d_size;
obj->efile.jumptables_data_shndx = idx;
+ } else if (strcmp(name, KMODS_BTFS_SEC) == 0) {
+ err = bpf_object__collect_kmod_btf_names(obj,
data, name);
+ if (err)
+ return err;
} else {
pr_info("elf: skipping unrecognized data
section(%d) %s\n",
idx, name);
@@ -5803,6 +5888,11 @@ int bpf_core_add_cands(struct bpf_core_cand *local_cand,
return 0;
}
+static bool is_kmod_btf_needed(struct bpf_object *obj, const char *name)
+{
+ return hashmap_find(obj->kmod_btfs->hashmap, (long)name, NULL);
+}
+
static int load_module_btfs(struct bpf_object *obj)
{
struct bpf_btf_info info;
@@ -5867,6 +5957,12 @@ static int load_module_btfs(struct bpf_object *obj)
continue;
}
+ if (obj->kmod_btfs && obj->kmod_btfs->hashmap &&
+ !is_kmod_btf_needed(obj, name)) {
+ close(fd);
+ continue;
+ }
+
btf = btf_get_from_fd(fd, obj->btf_vmlinux);
err = libbpf_get_error(btf);
if (err) {
@@ -5891,6 +5987,10 @@ static int load_module_btfs(struct bpf_object *obj)
break;
}
obj->btf_module_cnt++;
+
+ if (obj->kmod_btfs &&
+ obj->kmod_btfs->nr_names == obj->kmod_btfs->nr_loaded)
+ break;
}
if (err) {
@@ -9030,6 +9130,12 @@ static void bpf_object_cleanup_btf(struct bpf_object
*obj)
/* clean up vmlinux BTF */
btf__free(obj->btf_vmlinux);
obj->btf_vmlinux = NULL;
+
+ if (obj->kmod_btfs) {
+ hashmap__free(obj->kmod_btfs->hashmap);
+ zfree(&obj->kmod_btfs->data);
+ zfree(&obj->kmod_btfs);
+ }
}
static void bpf_object_post_load_cleanup(struct bpf_object *obj)
--
2.34.1
