[PATCH RFC bpf-next 01/52] libbpf: factor out BTF loading from load_module_btfs()

Alexander Lobakin
2022-06-28T19:51:01Z

From: Larysa Zaremba <larysa.zaremba@intel.com>

In order to be able to reuse BTF loading logics, move it to the new
btf_load_next_with_info() and call it from load_module_btfs()
instead.
To still be able to get the ID, introduce the ID field to the
userspace struct btf and return it via the new btf_obj_id().
To still be able to use bpf_btf_info::name as a string, locally add
a counterpart to ptr_to_u64() - u64_to_ptr() and use it to filter
vmlinux/module BTFs.
Also, add a definition for easy bpf_btf_info name declaration and
make btf_get_from_fd() static as it's now used only in btf.c.

Signed-off-by: Larysa Zaremba <larysa.zaremba@intel.com>
Signed-off-by: Alexander Lobakin <alexandr.lobakin@intel.com>
---
tools/lib/bpf/btf.c | 110 +++++++++++++++++++++++++++++++-
tools/lib/bpf/libbpf.c | 52 ++++-----------
tools/lib/bpf/libbpf_internal.h | 7 +-
3 files changed, 126 insertions(+), 43 deletions(-)

diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
index ae1520f7e1b0..7e4dbf71fd52 100644
--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -121,6 +121,9 @@ struct btf {

/* Pointer size (in bytes) for a target architecture of this BTF */
int ptr_sz;
+
+ /* BTF object ID, valid for vmlinux and module BTF */
+ __u32 id;
};

static inline __u64 ptr_to_u64(const void *ptr)
@@ -128,6 +131,11 @@ static inline __u64 ptr_to_u64(const void *ptr)
return (__u64) (unsigned long) ptr;
}

+static inline const void *u64_to_ptr(__u64 val)
+{
+ return (const void *)(unsigned long)val;
+}
+
/* Ensure given dynamically allocated memory region pointed to by *data* with
* capacity of *cap_cnt* elements each taking *elem_sz* bytes has enough
* memory to accommodate *add_cnt* new elements, assuming *cur_cnt* elements
@@ -463,6 +471,11 @@ const struct btf *btf__base_btf(const struct btf *btf)
return btf->base_btf;
}

+__u32 btf_obj_id(const struct btf *btf)
+{
+ return btf->id;
+}
+
/* internal helper returning non-const pointer to a type */
struct btf_type *btf_type_by_id(const struct btf *btf, __u32 type_id)
{
@@ -819,6 +832,7 @@ static struct btf *btf_new_empty(struct btf *base_btf)
btf->fd = -1;
btf->ptr_sz = sizeof(void *);
btf->swapped_endian = false;
+ btf->id = 0;

if (base_btf) {
btf->base_btf = base_btf;
@@ -869,6 +883,7 @@ static struct btf *btf_new(const void *data, __u32 size, struct btf *base_btf)
btf->start_id = 1;
btf->start_str_off = 0;
btf->fd = -1;
+ btf->id = 0;

if (base_btf) {
btf->base_btf = base_btf;
@@ -1334,7 +1349,7 @@ const char *btf__name_by_offset(const struct btf *btf, __u32 offset)
return btf__str_by_offset(btf, offset);
}

-struct btf *btf_get_from_fd(int btf_fd, struct btf *base_btf)
+static struct btf *btf_get_from_fd(int btf_fd, struct btf *base_btf)
{
struct bpf_btf_info btf_info;
__u32 len = sizeof(btf_info);
@@ -1382,6 +1397,8 @@ struct btf *btf_get_from_fd(int btf_fd, struct btf *base_btf)
}

btf = btf_new(ptr, btf_info.btf_size, base_btf);
+ if (!IS_ERR_OR_NULL(btf))
+ btf->id = btf_info.id;

exit_free:
free(ptr);
@@ -4819,6 +4836,97 @@ static int btf_dedup_remap_types(struct btf_dedup *d)
return 0;
}

+/**
+ * btf_load_next_with_info - get first BTF with ID bigger than the input one.
+ * @start_id: ID to start the search from
+ * @info: buffer to put BTF info to
+ * @base_btf: base BTF, can be %NULL if @vmlinux is true
+ * @vmlinux: true to look for the vmlinux BTF instead of a module BTF
+ *
+ * Obtains the first BTF with the ID bigger than the @start_id. @info::name and
+ * @info::name_len must be initialized by the caller. The default name buffer
+ * size is %BTF_NAME_BUF_LEN.
+ * FD must be closed after BTF is no longer needed. If @vmlinux is true, FD can
+ * be closed and set to -1 right away without preventing later usage.
+ *
+ * Returns pointer to the BTF loaded from the kernel or an error pointer.
+ */
+struct btf *btf_load_next_with_info(__u32 start_id, struct bpf_btf_info *info,
+ struct btf *base_btf, bool vmlinux)
+{
+ __u32 name_len = info->name_len;
+ __u64 name = info->name;
+ const char *name_str;
+ __u32 id = start_id;
+
+ if (!name)
+ return ERR_PTR(-EINVAL);
+
+ name_str = u64_to_ptr(name);
+
+ while (true) {
+ __u32 len = sizeof(*info);
+ struct btf *btf;
+ int err, fd;
+
+ err = bpf_btf_get_next_id(id, &id);
+ if (err) {
+ err = -errno;
+ if (err != -ENOENT)
+ pr_warn("failed to iterate BTF objects: %d\n",
+ err);
+ return ERR_PTR(err);
+ }
+
+ fd = bpf_btf_get_fd_by_id(id);
+ if (fd < 0) {
+ err = -errno;
+ if (err == -ENOENT)
+ /* Expected race: non-vmlinux BTF was
+ * unloaded
+ */
+ continue;
+ pr_warn("failed to get BTF object #%d FD: %d\n",
+ id, err);
+ return ERR_PTR(err);
+ }
+
+ memset(info, 0, len);
+ info->name = name;
+ info->name_len = name_len;
+
+ err = bpf_obj_get_info_by_fd(fd, info, &len);
+ if (err) {
+ err = -errno;
+ pr_warn("failed to get BTF object #%d info: %d\n",
+ id, err);
+ goto err_out;
+ }
+
+ /* Filter BTFs */
+ if (!info->kernel_btf ||
+ !strcmp(name_str, "vmlinux") != vmlinux) {
+ close(fd);
+ continue;
+ }
+
+ btf = btf_get_from_fd(fd, base_btf);
+ err = libbpf_get_error(btf);
+ if (err) {
+ pr_warn("failed to load module [%s]'s BTF object #%d: %d\n",
+ name_str, id, err);
+ goto err_out;
+ }
+
+ btf->fd = fd;
+ return btf;
+
+err_out:
+ close(fd);
+ return ERR_PTR(err);
+ }
+}
+
/*
* Probe few well-known locations for vmlinux kernel image and try to load BTF
* data out of it to use for target BTF.
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 335467ece75f..8e27bad5e80f 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -5559,11 +5559,11 @@ int bpf_core_add_cands(struct bpf_core_cand *local_cand,

static int load_module_btfs(struct bpf_object *obj)
{
- struct bpf_btf_info info;
+ char name[BTF_NAME_BUF_LEN] = { };
struct module_btf *mod_btf;
+ struct bpf_btf_info info;
struct btf *btf;
- char name[64];
- __u32 id = 0, len;
+ __u32 id = 0;
int err, fd;

if (obj->btf_modules_loaded)
@@ -5580,49 +5580,19 @@ static int load_module_btfs(struct bpf_object *obj)
return 0;

while (true) {
- err = bpf_btf_get_next_id(id, &id);
- if (err && errno == ENOENT)
- return 0;
- if (err) {
- err = -errno;
- pr_warn("failed to iterate BTF objects: %d\n", err);
- return err;
- }
-
- fd = bpf_btf_get_fd_by_id(id);
- if (fd < 0) {
- if (errno == ENOENT)
- continue; /* expected race: BTF was unloaded */
- err = -errno;
- pr_warn("failed to get BTF object #%d FD: %d\n", id, err);
- return err;
- }
-
- len = sizeof(info);
memset(&info, 0, sizeof(info));
info.name = ptr_to_u64(name);
info.name_len = sizeof(name);

- err = bpf_obj_get_info_by_fd(fd, &info, &len);
- if (err) {
- err = -errno;
- pr_warn("failed to get BTF object #%d info: %d\n", id, err);
- goto err_out;
- }
-
- /* ignore non-module BTFs */
- if (!info.kernel_btf || strcmp(name, "vmlinux") == 0) {
- close(fd);
- continue;
- }
-
- btf = btf_get_from_fd(fd, obj->btf_vmlinux);
+ btf = btf_load_next_with_info(id, &info, obj->btf_vmlinux,
+ false);
err = libbpf_get_error(btf);
- if (err) {
- pr_warn("failed to load module [%s]'s BTF object #%d: %d\n",
- name, id, err);
- goto err_out;
- }
+ if (err)
+ return err == -ENOENT ? 0 : err;
+
+ fd = btf__fd(btf);
+ btf__set_fd(btf, -1);
+ id = btf_obj_id(btf);

err = libbpf_ensure_mem((void **)&obj->btf_modules, &obj->btf_module_cap,
sizeof(*obj->btf_modules), obj->btf_module_cnt + 1);
diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h
index a1ad145ffa74..9b0bbd4a5f64 100644
--- a/tools/lib/bpf/libbpf_internal.h
+++ b/tools/lib/bpf/libbpf_internal.h
@@ -366,9 +366,14 @@ int libbpf__load_raw_btf(const char *raw_types, size_t types_len,
const char *str_sec, size_t str_len);
int btf_load_into_kernel(struct btf *btf, char *log_buf, size_t log_sz, __u32 log_level);

-struct btf *btf_get_from_fd(int btf_fd, struct btf *base_btf);
void btf_get_kernel_prefix_kind(enum bpf_attach_type attach_type,
const char **prefix, int *kind);
+__u32 btf_obj_id(const struct btf *btf);
+
+#define BTF_NAME_BUF_LEN 64
+
+struct btf *btf_load_next_with_info(__u32 start_id, struct bpf_btf_info *info,
+ struct btf *base_btf, bool vmlinux);

struct btf_ext_info {
/*
--
2.36.1