Merge branch 'skel-fixes'

Andrii Nakryiko says:

====================
Simplify skeleton usage by embedding source BPF object file inside skeleton
itself. This allows to keep skeleton and object file in sync at all times with
no chance of confusion.

Also, add bpftool-gen.rst manpage, explaining concepts and ideas behind
skeleton. In examples section it also includes a complete small BPF
application utilizing skeleton, as a demonstration of API.

Patch #2 also removes BPF_EMBED_OBJ, as there is currently no use of it.

v2->v3:
- (void) in no-args function (Alexei);
- bpftool-gen.rst code block formatting fix (Alexei);
- simplified xxx__create_skeleton to fill in obj and return error code;

v1->v2:
- remove whitespace from empty lines in code blocks (Yonghong).
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>

3 files changed, 449 insertions, 90 deletions

diff --git a/tools/bpf/bpftool/Documentation/bpftool-gen.rst b/tools/bpf/bpftool/Documentation/bpftool-gen.rst
new file mode 100644
index 000000000000..b6a114bf908d
--- /dev/null
+++ b/tools/bpf/bpftool/Documentation/bpftool-gen.rst
@@ -0,0 +1,304 @@
+================
+bpftool-gen
+================
+-------------------------------------------------------------------------------
+tool for BPF code-generation
+-------------------------------------------------------------------------------
+
+:Manual section: 8
+
+SYNOPSIS
+========
+
+	**bpftool** [*OPTIONS*] **gen** *COMMAND*
+
+	*OPTIONS* := { { **-j** | **--json** } [{ **-p** | **--pretty** }] }
+
+	*COMMAND* := { **skeleton | **help** }
+
+GEN COMMANDS
+=============
+
+|	**bpftool** **gen skeleton** *FILE*
+|	**bpftool** **gen help**
+
+DESCRIPTION
+===========
+	**bpftool gen skeleton** *FILE*
+		  Generate BPF skeleton C header file for a given *FILE*.
+
+		  BPF skeleton is an alternative interface to existing libbpf
+		  APIs for working with BPF objects. Skeleton code is intended
+		  to significantly shorten and simplify code to load and work
+		  with BPF programs from userspace side. Generated code is
+		  tailored to specific input BPF object *FILE*, reflecting its
+		  structure by listing out available maps, program, variables,
+		  etc. Skeleton eliminates the need to lookup mentioned
+		  components by name. Instead, if skeleton instantiation
+		  succeeds, they are populated in skeleton structure as valid
+		  libbpf types (e.g., struct bpf_map pointer) and can be
+		  passed to existing generic libbpf APIs.
+
+		  In addition to simple and reliable access to maps and
+		  programs, skeleton provides a storage for BPF links (struct
+		  bpf_link) for each BPF program within BPF object. When
+		  requested, supported BPF programs will be automatically
+		  attached and resulting BPF links stored for further use by
+		  user in pre-allocated fields in skeleton struct. For BPF
+		  programs that can't be automatically attached by libbpf,
+		  user can attach them manually, but store resulting BPF link
+		  in per-program link field. All such set up links will be
+		  automatically destroyed on BPF skeleton destruction. This
+		  eliminates the need for users to manage links manually and
+		  rely on libbpf support to detach programs and free up
+		  resources.
+
+		  Another facility provided by BPF skeleton is an interface to
+		  global variables of all supported kinds: mutable, read-only,
+		  as well as extern ones. This interface allows to pre-setup
+		  initial values of variables before BPF object is loaded and
+		  verified by kernel. For non-read-only variables, the same
+		  interface can be used to fetch values of global variables on
+		  userspace side, even if they are modified by BPF code.
+
+		  During skeleton generation, contents of source BPF object
+		  *FILE* is embedded within generated code and is thus not
+		  necessary to keep around. This ensures skeleton and BPF
+		  object file are matching 1-to-1 and always stay in sync.
+		  Generated code is dual-licensed under LGPL-2.1 and
+		  BSD-2-Clause licenses.
+
+		  It is a design goal and guarantee that skeleton interfaces
+		  are interoperable with generic libbpf APIs. User should
+		  always be able to use skeleton API to create and load BPF
+		  object, and later use libbpf APIs to keep working with
+		  specific maps, programs, etc.
+
+		  As part of skeleton, few custom functions are generated.
+		  Each of them is prefixed with object name, derived from
+		  object file name. I.e., if BPF object file name is
+		  **example.o**, BPF object name will be **example**. The
+		  following custom functions are provided in such case:
+
+		  - **example__open** and **example__open_opts**.
+		    These functions are used to instantiate skeleton. It
+		    corresponds to libbpf's **bpf_object__open()** API.
+		    **_opts** variants accepts extra **bpf_object_open_opts**
+		    options.
+
+		  - **example__load**.
+		    This function creates maps, loads and verifies BPF
+		    programs, initializes global data maps. It corresponds to
+		    libppf's **bpf_object__load** API.
+
+		  - **example__open_and_load** combines **example__open** and
+		    **example__load** invocations in one commonly used
+		    operation.
+
+		  - **example__attach** and **example__detach**
+		    This pair of functions allow to attach and detach,
+		    correspondingly, already loaded BPF object. Only BPF
+		    programs of types supported by libbpf for auto-attachment
+		    will be auto-attached and their corresponding BPF links
+		    instantiated. For other BPF programs, user can manually
+		    create a BPF link and assign it to corresponding fields in
+		    skeleton struct. **example__detach** will detach both
+		    links created automatically, as well as those populated by
+		    user manually.
+
+		  - **example__destroy**
+		    Detach and unload BPF programs, free up all the resources
+		    used by skeleton and BPF object.
+
+		  If BPF object has global variables, corresponding structs
+		  with memory layout corresponding to global data data section
+		  layout will be created. Currently supported ones are: .data,
+		  .bss, .rodata, and .extern structs/data sections. These
+		  data sections/structs can be used to set up initial values of
+		  variables, if set before **example__load**. Afterwards, if
+		  target kernel supports memory-mapped BPF arrays, same
+		  structs can be used to fetch and update (non-read-only)
+		  data from userspace, with same simplicity as for BPF side.
+
+	**bpftool gen help**
+		  Print short help message.
+
+OPTIONS
+=======
+	-h, --help
+		  Print short generic help message (similar to **bpftool help**).
+
+	-V, --version
+		  Print version number (similar to **bpftool version**).
+
+	-j, --json
+		  Generate JSON output. For commands that cannot produce JSON,
+		  this option has no effect.
+
+	-p, --pretty
+		  Generate human-readable JSON output. Implies **-j**.
+
+	-d, --debug
+		  Print all logs available from libbpf, including debug-level
+		  information.
+
+EXAMPLES
+========
+**$ cat example.c**
+::
+
+  #include <stdbool.h>
+  #include <linux/ptrace.h>
+  #include <linux/bpf.h>
+  #include "bpf_helpers.h"
+
+  const volatile int param1 = 42;
+  bool global_flag = true;
+  struct { int x; } data = {};
+
+  struct {
+  	__uint(type, BPF_MAP_TYPE_HASH);
+  	__uint(max_entries, 128);
+  	__type(key, int);
+  	__type(value, long);
+  } my_map SEC(".maps");
+
+  SEC("raw_tp/sys_enter")
+  int handle_sys_enter(struct pt_regs *ctx)
+  {
+  	static long my_static_var;
+  	if (global_flag)
+  		my_static_var++;
+  	else
+  		data.x += param1;
+  	return 0;
+  }
+
+  SEC("raw_tp/sys_exit")
+  int handle_sys_exit(struct pt_regs *ctx)
+  {
+  	int zero = 0;
+  	bpf_map_lookup_elem(&my_map, &zero);
+  	return 0;
+  }
+
+This is example BPF application with two BPF programs and a mix of BPF maps
+and global variables.
+
+**$ bpftool gen skeleton example.o**
+::
+
+  /* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */
+
+  /* THIS FILE IS AUTOGENERATED! */
+  #ifndef __EXAMPLE_SKEL_H__
+  #define __EXAMPLE_SKEL_H__
+
+  #include <stdlib.h>
+  #include <libbpf.h>
+
+  struct example {
+  	struct bpf_object_skeleton *skeleton;
+  	struct bpf_object *obj;
+  	struct {
+  		struct bpf_map *rodata;
+  		struct bpf_map *data;
+  		struct bpf_map *bss;
+  		struct bpf_map *my_map;
+  	} maps;
+  	struct {
+  		struct bpf_program *handle_sys_enter;
+  		struct bpf_program *handle_sys_exit;
+  	} progs;
+  	struct {
+  		struct bpf_link *handle_sys_enter;
+  		struct bpf_link *handle_sys_exit;
+  	} links;
+  	struct example__bss {
+  		struct {
+  			int x;
+  		} data;
+  	} *bss;
+  	struct example__data {
+  		_Bool global_flag;
+  		long int handle_sys_enter_my_static_var;
+  	} *data;
+  	struct example__rodata {
+  		int param1;
+  	} *rodata;
+  };
+
+  static void example__destroy(struct example *obj);
+  static inline struct example *example__open_opts(
+                const struct bpf_object_open_opts *opts);
+  static inline struct example *example__open();
+  static inline int example__load(struct example *obj);
+  static inline struct example *example__open_and_load();
+  static inline int example__attach(struct example *obj);
+  static inline void example__detach(struct example *obj);
+
+  #endif /* __EXAMPLE_SKEL_H__ */
+
+**$ cat example_user.c**
+::
+
+  #include "example.skel.h"
+
+  int main()
+  {
+  	struct example *skel;
+  	int err = 0;
+
+  	skel = example__open();
+  	if (!skel)
+  		goto cleanup;
+
+  	skel->rodata->param1 = 128;
+
+  	err = example__load(skel);
+  	if (err)
+  		goto cleanup;
+
+  	err = example__attach(skel);
+  	if (err)
+  		goto cleanup;
+
+  	/* all libbpf APIs are usable */
+  	printf("my_map name: %s\n", bpf_map__name(skel->maps.my_map));
+  	printf("sys_enter prog FD: %d\n",
+  	       bpf_program__fd(skel->progs.handle_sys_enter));
+
+  	/* detach and re-attach sys_exit program */
+  	bpf_link__destroy(skel->links.handle_sys_exit);
+  	skel->links.handle_sys_exit =
+  		bpf_program__attach(skel->progs.handle_sys_exit);
+
+  	printf("my_static_var: %ld\n",
+  	       skel->bss->handle_sys_enter_my_static_var);
+
+  cleanup:
+  	example__destroy(skel);
+  	return err;
+  }
+
+**# ./example_user**
+::
+
+  my_map name: my_map
+  sys_enter prog FD: 8
+  my_static_var: 7
+
+This is a stripped-out version of skeleton generated for above example code.
+
+SEE ALSO
+========
+	**bpf**\ (2),
+	**bpf-helpers**\ (7),
+	**bpftool**\ (8),
+	**bpftool-map**\ (8),
+	**bpftool-prog**\ (8),
+	**bpftool-cgroup**\ (8),
+	**bpftool-feature**\ (8),
+	**bpftool-net**\ (8),
+	**bpftool-perf**\ (8),
+	**bpftool-btf**\ (8)
diff --git a/tools/bpf/bpftool/Documentation/bpftool.rst b/tools/bpf/bpftool/Documentation/bpftool.rst
index 6a9c52ef84a9..34239fda69ed 100644
--- a/tools/bpf/bpftool/Documentation/bpftool.rst
+++ b/tools/bpf/bpftool/Documentation/bpftool.rst
@@ -81,4 +81,5 @@ SEE ALSO
 	**bpftool-feature**\ (8),
 	**bpftool-net**\ (8),
 	**bpftool-perf**\ (8),
-	**bpftool-btf**\ (8)
+	**bpftool-btf**\ (8),
+	**bpftool-gen**\ (8),
diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
index f70088b4c19b..8d93c8f90f82 100644
--- a/tools/bpf/bpftool/gen.c
+++ b/tools/bpf/bpftool/gen.c
@@ -16,6 +16,7 @@
 #include <libbpf.h>
 #include <sys/types.h>
 #include <sys/stat.h>
+#include <sys/mman.h>
 #include <unistd.h>
 
 #include "btf.h"
@@ -261,14 +262,16 @@ static int codegen(const char *template, ...)
 static int do_skeleton(int argc, char **argv)
 {
 	char header_guard[MAX_OBJ_NAME_LEN + sizeof("__SKEL_H__")];
-	size_t i, map_cnt = 0, prog_cnt = 0;
-	char obj_name[MAX_OBJ_NAME_LEN];
+	size_t i, map_cnt = 0, prog_cnt = 0, file_sz, mmap_sz;
+	DECLARE_LIBBPF_OPTS(bpf_object_open_opts, opts);
+	char obj_name[MAX_OBJ_NAME_LEN], *obj_data;
+	struct bpf_object *obj = NULL;
 	const char *file, *ident;
 	struct bpf_program *prog;
-	struct bpf_object *obj;
+	int fd, len, err = -1;
 	struct bpf_map *map;
 	struct btf *btf;
-	int err = -1;
+	struct stat st;
 
 	if (!REQ_ARGS(1)) {
 		usage();
@@ -281,14 +284,31 @@ static int do_skeleton(int argc, char **argv)
 		return -1;
 	}
 
-	obj = bpf_object__open_file(file, NULL);
-	if (IS_ERR(obj)) {
-		p_err("failed to open BPF object file: %ld", PTR_ERR(obj));
+	if (stat(file, &st)) {
+		p_err("failed to stat() %s: %s", file, strerror(errno));
 		return -1;
 	}
-
+	file_sz = st.st_size;
+	mmap_sz = roundup(file_sz, sysconf(_SC_PAGE_SIZE));
+	fd = open(file, O_RDONLY);
+	if (fd < 0) {
+		p_err("failed to open() %s: %s", file, strerror(errno));
+		return -1;
+	}
+	obj_data = mmap(NULL, mmap_sz, PROT_READ, MAP_PRIVATE, fd, 0);
+	if (obj_data == MAP_FAILED) {
+		obj_data = NULL;
+		p_err("failed to mmap() %s: %s", file, strerror(errno));
+		goto out;
+	}
 	get_obj_name(obj_name, file);
-	get_header_guard(header_guard, obj_name);
+	opts.object_name = obj_name;
+	obj = bpf_object__open_mem(obj_data, file_sz, &opts);
+	if (IS_ERR(obj)) {
+		obj = NULL;
+		p_err("failed to open BPF object file: %ld", PTR_ERR(obj));
+		goto out;
+	}
 
 	bpf_object__for_each_map(map, obj) {
 		ident = get_map_ident(map);
@@ -303,8 +323,11 @@ static int do_skeleton(int argc, char **argv)
 		prog_cnt++;
 	}
 
+	get_header_guard(header_guard, obj_name);
 	codegen("\
 		\n\
+		/* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */   \n\
+									    \n\
 		/* THIS FILE IS AUTOGENERATED! */			    \n\
 		#ifndef %2$s						    \n\
 		#define %2$s						    \n\
@@ -356,19 +379,95 @@ static int do_skeleton(int argc, char **argv)
 		\n\
 		};							    \n\
 									    \n\
-		static inline struct bpf_object_skeleton *		    \n\
-		%1$s__create_skeleton(struct %1$s *obj, struct bpf_embed_data *embed)\n\
+		static void						    \n\
+		%1$s__destroy(struct %1$s *obj)				    \n\
+		{							    \n\
+			if (!obj)					    \n\
+				return;					    \n\
+			if (obj->skeleton)				    \n\
+				bpf_object__destroy_skeleton(obj->skeleton);\n\
+			free(obj);					    \n\
+		}							    \n\
+									    \n\
+		static inline int					    \n\
+		%1$s__create_skeleton(struct %1$s *obj);		    \n\
+									    \n\
+		static inline struct %1$s *				    \n\
+		%1$s__open_opts(const struct bpf_object_open_opts *opts)    \n\
+		{							    \n\
+			struct %1$s *obj;				    \n\
+									    \n\
+			obj = calloc(1, sizeof(*obj));			    \n\
+			if (!obj)					    \n\
+				return NULL;				    \n\
+			if (%1$s__create_skeleton(obj))			    \n\
+				goto err;				    \n\
+			if (bpf_object__open_skeleton(obj->skeleton, opts)) \n\
+				goto err;				    \n\
+									    \n\
+			return obj;					    \n\
+		err:							    \n\
+			%1$s__destroy(obj);				    \n\
+			return NULL;					    \n\
+		}							    \n\
+									    \n\
+		static inline struct %1$s *				    \n\
+		%1$s__open(void)					    \n\
+		{							    \n\
+			return %1$s__open_opts(NULL);			    \n\
+		}							    \n\
+									    \n\
+		static inline int					    \n\
+		%1$s__load(struct %1$s *obj)				    \n\
+		{							    \n\
+			return bpf_object__load_skeleton(obj->skeleton);    \n\
+		}							    \n\
+									    \n\
+		static inline struct %1$s *				    \n\
+		%1$s__open_and_load(void)				    \n\
+		{							    \n\
+			struct %1$s *obj;				    \n\
+									    \n\
+			obj = %1$s__open();				    \n\
+			if (!obj)					    \n\
+				return NULL;				    \n\
+			if (%1$s__load(obj)) {				    \n\
+				%1$s__destroy(obj);			    \n\
+				return NULL;				    \n\
+			}						    \n\
+			return obj;					    \n\
+		}							    \n\
+									    \n\
+		static inline int					    \n\
+		%1$s__attach(struct %1$s *obj)				    \n\
+		{							    \n\
+			return bpf_object__attach_skeleton(obj->skeleton);  \n\
+		}							    \n\
+									    \n\
+		static inline void					    \n\
+		%1$s__detach(struct %1$s *obj)				    \n\
+		{							    \n\
+			return bpf_object__detach_skeleton(obj->skeleton);  \n\
+		}							    \n\
+		",
+		obj_name
+	);
+
+	codegen("\
+		\n\
+									    \n\
+		static inline int					    \n\
+		%1$s__create_skeleton(struct %1$s *obj)			    \n\
 		{							    \n\
 			struct bpf_object_skeleton *s;			    \n\
 									    \n\
 			s = calloc(1, sizeof(*s));			    \n\
 			if (!s)						    \n\
-				return NULL;				    \n\
+				return -1;				    \n\
+			obj->skeleton = s;				    \n\
 									    \n\
 			s->sz = sizeof(*s);				    \n\
 			s->name = \"%1$s\";				    \n\
-			s->data = embed->data;				    \n\
-			s->data_sz = embed->size;			    \n\
 			s->obj = &obj->obj;				    \n\
 		",
 		obj_name
@@ -438,90 +537,45 @@ static int do_skeleton(int argc, char **argv)
 	codegen("\
 		\n\
 									    \n\
-			return s;					    \n\
-		err:							    \n\
-			bpf_object__destroy_skeleton(s);		    \n\
-			return NULL;					    \n\
-		}							    \n\
-									    \n\
-		static void						    \n\
-		%1$s__destroy(struct %1$s *obj)				    \n\
-		{							    \n\
-			if (!obj)					    \n\
-				return;					    \n\
-			if (obj->skeleton)				    \n\
-				bpf_object__destroy_skeleton(obj->skeleton);\n\
-			free(obj);					    \n\
-		}							    \n\
-									    \n\
-		static inline struct %1$s *				    \n\
-		%1$s__open_opts(struct bpf_embed_data *embed, const struct bpf_object_open_opts *opts)\n\
-		{							    \n\
-			struct %1$s *obj;				    \n\
-									    \n\
-			obj = calloc(1, sizeof(*obj));			    \n\
-			if (!obj)					    \n\
-				return NULL;				    \n\
-									    \n\
-			obj->skeleton = %1$s__create_skeleton(obj, embed);  \n\
-			if (!obj->skeleton)				    \n\
-				goto err;				    \n\
-									    \n\
-			if (bpf_object__open_skeleton(obj->skeleton, opts)) \n\
-				goto err;				    \n\
+			s->data_sz = %d;				    \n\
+			s->data = \"\\					    \n\
+		",
+		file_sz);
+
+	/* embed contents of BPF object file */
+	for (i = 0, len = 0; i < file_sz; i++) {
+		int w = obj_data[i] ? 4 : 2;
+
+		len += w;
+		if (len > 78) {
+			printf("\\\n");
+			len = w;
+		}
+		if (!obj_data[i])
+			printf("\\0");
+		else
+			printf("\\x%02x", (unsigned char)obj_data[i]);
+	}
+
+	codegen("\
+		\n\
+		\";							    \n\
 									    \n\
-			return obj;					    \n\
+			return 0;					    \n\
 		err:							    \n\
-			%1$s__destroy(obj);				    \n\
-			return NULL;					    \n\
-		}							    \n\
-									    \n\
-		static inline struct %1$s *				    \n\
-		%1$s__open(struct bpf_embed_data *embed)		    \n\
-		{							    \n\
-			return %1$s__open_opts(embed, NULL);		    \n\
-		}							    \n\
-									    \n\
-		static inline int					    \n\
-		%1$s__load(struct %1$s *obj)				    \n\
-		{							    \n\
-			return bpf_object__load_skeleton(obj->skeleton);    \n\
-		}							    \n\
-									    \n\
-		static inline struct %1$s *				    \n\
-		%1$s__open_and_load(struct bpf_embed_data *embed)	    \n\
-		{							    \n\
-			struct %1$s *obj;				    \n\
-									    \n\
-			obj = %1$s__open(embed);			    \n\
-			if (!obj)					    \n\
-				return NULL;				    \n\
-			if (%1$s__load(obj)) {				    \n\
-				%1$s__destroy(obj);			    \n\
-				return NULL;				    \n\
-			}						    \n\
-			return obj;					    \n\
-		}							    \n\
-									    \n\
-		static inline int					    \n\
-		%1$s__attach(struct %1$s *obj)				    \n\
-		{							    \n\
-			return bpf_object__attach_skeleton(obj->skeleton);  \n\
-		}							    \n\
-									    \n\
-		static inline void					    \n\
-		%1$s__detach(struct %1$s *obj)				    \n\
-		{							    \n\
-			return bpf_object__detach_skeleton(obj->skeleton);  \n\
+			bpf_object__destroy_skeleton(s);		    \n\
+			return -1;					    \n\
 		}							    \n\
 									    \n\
 		#endif /* %2$s */					    \n\
 		",
-		obj_name, header_guard
-	);
+		obj_name, header_guard);
 	err = 0;
 out:
 	bpf_object__close(obj);
+	if (obj_data)
+		munmap(obj_data, mmap_sz);
+	close(fd);
 	return err;
 }