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

[Alexander Lobakin]

From: Larysa Zaremba <larysa.zaremba@xxxxxxxxx>

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@xxxxxxxxx>
Signed-off-by: Alexander Lobakin <alexandr.lobakin@xxxxxxxxx>
---
 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